EPA-600/1-76-012
January 1976
Environmental Health Effects Research Series
Optimization and Evaluation of a
MICROELECTROLYTIC CONDUCTIVITY DETECTOR FOR
THE GAS CHROMATOGRAPHIC DETERMINATION OF
PESTICIDE RESIDUES
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
^search Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development,
U.S. Environmental Protection Agency, have been grouped into
five series. These five broad categories were established to
facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in
related fields. The five sefies
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL HEALTH EFFECTS
RESEARCH series. This series describes projects and studies relating
to the tolerances of man for unhealthful substances or conditions.
This work is generally assessed from a medical viewpoint, including
physiological or psychological studies. In addition to toxicology
and other medical specialities, study areas include biomedical
instrumentation and health research techniques utilizing animals -
but always with intended application to human health measures.
This document is available to the public through the National
Technical Information Service, Springfield, Virginia 22161.
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EPA-600/1-76-012
January 1976
OPTIMIZATION AND EVALUATION OF A
MICROELECTROLYTIC CONDUCTIVITY DETECTOR FOR
THE GAS CHROMATOGRAPHIC DETERMINATION
OF PESTICIDE RESIDUES
By
Randall C. Hall
Department of Entomology
Purdue University
West Lafayette, Indiana 47907
Contract No. 68-02-1703
Project Officer
Robert G. Lewis, Ph.D.
Environmental Toxicology Division
Health Effects Research Laboratory
Research Triangle Park, N.C. 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
HEALTH EFFECTS RESEARCH LABORATORY
RESEARCH TRIANGLE PARK, N.C. 27711
-------
DISCLAIMER
This report has been reviewed by the Health Effects Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily
reflect the views and policies of the IJ.S. Environmental Protection
Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
ii
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CONTENTS
Page
SCOPE OF WORK 1
DETECTOR OPERATION 3
Detection of Halogen Containing Compounds 4
Detection of Sulfur Containing Compounds • 48
Detection of Nitrogen Containing Compounds 98
APPLICATIONS 115
Analysis of Chlorine Containing Pesticides in the presence 116
of PCB and PCN in Water, Soil, and Biological Samples
Analysis of Sulfur Containing Pesticides in Water, Soil, and 127
Biological Samples
Analysis of Nitrogen Containing Pesticides in Water, Soil, 141
and Biological Samples
RECOMMENDED OPERATING CONDITIONS AND MAINTENANCE 153
BIBLIOGRAPHY 160
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SCOPE OF WORK
General
A microelectrolytic conductivity detector for gas chromatography was
recently developed at Purdue University, West Lafayette, Indiana. This
detector is manufactured and marketed by Tracer, Inc., Austin, Texas; and
replaces their Coulson electrolytic conductivity detector. The detector
is selective to halogen-, sulfur- and nitrogen-containing compounds, and has
subnanogram sensitivity with a relatively wide linear dynamic range.
The high sensitivity, selectivity and linearity of the detector should
make it a valuable analytical instrument for contaminant monitoring. However,
since the detector has been available for only a short time, the analytical
potential of this device is not known. It was the purpose of this contract
to optimize and fully evaluate the microelectrolytic conductivity detector for
the sensitive detection of nitrogen-, halogen-and sulfur-containing pesticides
in environmental samples-
Specifics
In performance of the technical effort, the Contractor has:
a. Optimized and evaluated the detector for the determination of
chlorinated hydrocarbons (pesticides and toxic substances) in water, soil
and animal tissue substrates at the most sensitive practical levels of
detection.
b. Demonstrated the usefulness of the detector for differentiating between
chlorinated hydrocarbon pesticides and polychlorinated biphenyls and polychlori-
nated naphthalenes at the residue level using environmental and biological samples,
-------
c. Optimized and evaluated the detector system for selective, subnanogram
sensitivity to nitrogen-containing compounds in a representative variety of
sample types, including water, soil and biological tissues.
d. Optimized and evaluated the detector for selective, subnanogram
sensitivity to sulfur-containing pesticides in a representative variety of
sample types, including water, soil and biological tissues.
e. Demonstrated the linearity of response, reliability and ease of
operation.
f. Delivered two modified detector systems to the Project Officer.
-------
DETECTOR OPERATION
Experimental Conditions
Apparatus. Tracer Model 310 Hall electrolytic conductivity detectors
and laboratory prototype detectors were used throughout this study. The com-
mercial detector was modified by incorporating a solvent vent and decreasing
the recorder attenuator factor of the conductivity meter from a value of 1.0
to 0.1. The solvent vent was constructed from a 1/8-inch stainless steel
union by the addition of a 0.0625 inch o.d. X 0.03 inch i.d. X 2 ft. vent tube.
The end of the vent tube was connected to a Whitneytoggle valve (0.080 inch
orifice). A Teflon restrictor tube (1/16 inch o.d. X 0.02 inch i.d.) was
connected to the valve exit to provide sufficient back pressure so that the
carrier gas was vented and the reaction gas was not. The solvent vent was
interfaced to the chromatograph via 1/8-inch o.d. glass-lined stainless steel
tubing. The recorder attenuator factor was decreased by reducing the value
of the voltage divider resistor prior to the attenuator circuit from 1.24 M to
124 K.
Chrornatography. Halogen-and sulfur-containing pesticides were analyzed
using 1/4-in. o.d. X 2-mm. i.d. X 6-ft. glass columns containing 5% OV-101
on 80-100 mesh Gas Chrom Q operated at 210 and a helium carrier gas flow of
30-40 cc/rnin. Nitrogen containing pesticides were analyzed using 1/4-in. o.d. X
2-mm. i.d.. X 6-ft. silanized glass columns containing 1% Carbowax 20M operated
at 160 or 190° with a hydrogen carrier gas flow rate of 40 cc/min.
Tracor Models MT-220 and 550 gas chromatographs were used for the analysis
of halogen and sulfur pesticides. A Varian Model 1200 gas chromatograph was
used for the analysis of nitrogen pesticides. The inlet, outlet and transfer
temperatures on the MT-220 were 225, 235 and 245 respectively. The inlet and
outlet temperatures on the 550 were 235 and 275°. The Varian chromatograph
-------
inlet and outlet temperatures were 200 . The hydrogen gas used in the catalytic
reductive modes (halogen and nitrogen) was generated with an Elhygen hydrogen
generator.
Detection of Halogen Containing Compounds
Optimization of Detector Operating Conditions. Halogen-containing compounds
are detected as the strong acid MX. Chlorine containing compounds can be
converted to HC1 by pyrolysis (with only inert carrier gas), reductive pyrolysis,
oxidative pyrolysis* catalytic reduction or catalytic oxidation. Quartz tubing
is used in the pyrolytic modes, whereas nickel tubing is used in the catalytic modes,
Hydrogen is used as the reaction gas for the reductive modes and either air or
oxygen for the oxidative modes.
"Conductivity Solvent and Reaction Systems". The detection of trace
quantities of chlorine-containing compounds presents a number of problems. First,
the chlorinated compound must be converted to HC1 at a temperature of 600-950°.
At this temperature, most materials have considerable surface reactivity, and
great care must be exercised to prevent HC1 absorption. Second, HC1 is very
reactive and must be transported to the conductivity cell via an "inert" path.
Third, HC1 is a strong acid and impurities in the conductivity solvent may be
protonated, which can result in peak tailing and a loss in sensitivity.
Ideally, the conductivity solvent should be compatible with the ion
exchange resin, have a very low conductivity, effectively support conductance
of the monitored species, and present no health hazard. In an attempt to find
an appropriate solvent for the detection of halogen-containing compounds, a
wide variety of protic and aprotic solvents were investigated.
-------
Solvents were evaluated for specificity, linearity and sensitivity of
response using a "selectivity" sample mixture and a "pesticide" sample mixture.
The selectivity mixture was comprised of 2 yg of hexadecane, 100 ng of caffeine,
100 ng of parathion, 2 ng of heptachlor epoxide and 100 ng of ethyl stearate.
The pesticide mixture included lindane, heptachlor, aldrin, heptachlor epoxide
and dieldrin. The pesticide quantities ranged from 1 X 10~ g to 1 X 10 g
of each component.
Hexadecane was used to evaluate detector selectivity against hydrocarbons.
Caffeine, parathion and ethyl stearate represented compounds containing
nitrogen, sulfur and ester groups respectively. The compounds are unique
in the respect that they represent classes of compounds which exhibit a response
considerably greater than that of most other classes of compounds containing
these elements. Thus, they represent the greatest degree of interference that
should be encountered in the determination of halogen-containing compounds.
Detector sensitivity and selectivity were determined for the conductivity
solvents methyl alcohol, 50% ethyl alcohol, ethyl alcohol, isopropyl alcohol,
acetonitrile, diisopropyl ketone, nitroethane, nitrobenzene, benzene and
dimethyl formamide. Detector linearity to chlorinated hydrocarbon pesticides
was then determined for those solvents that exhibited good sensitivity
and selectivity. The evaluation was conducted in the pyrolytic mode using
hydrogen as the reaction gas and a 2-mrtK i.d. quartz reaction tube.
In general, absolute alcohols, and acetonitrile were the only solvents
which gave both high sensitivity and linearity of response. (See Figure
1-3). Acetonitrile appeared to alter the ion exchange resin and gave
erratic results. Dimethyl formamide and diisopropyl ketone were not
-------
>
E
e
e
a
«
d>
oc
B
l
2
r
4
i
0
Time (min.)
Figure 1. Chromatograms of the chlorinated pesticide mixture with
different conductivity solvents: A, acetonitrile, 20 ng
of each compound, 100 X 0.8; B, methyl alcohol, 10 ng
of each compound, 10 X 3.2.
-------
m
e
o
4) C9 ••
a
o
w-
Lindane
Dieldrin
i
•9
I
•8
log gram*
Figure 2. Linearity of response to lindane and dieldrin. Conditions
furnace temperature, 700°; H9 reaction gas, 0 cc/min;
conductivity solvent, methyl^alcohol; resin, IRN-150/77.
-------
8
Lindane
Dieldrin
•10 -9 -8
log grams
Figure 3. Linearity of response to lindane and dieldrin. Conditions
furnace temperature, 900°; H2 reaction gas; 5 cc/min,
conductivity solvent, acetonitrile; resin, ARM-381.
-------
compatible with the ion exchange resin and gave too high of a background to be
evaluated. Although selectivity for chlorine-containing compounds against
hydrocarbons was good, selectivity against caffeine, parathion and ethyl
stearate was poor for all the solvents investigated.
Selectivity for halogen-containing compounds (exemplified by heptachlor
epoxide) as a function of the conductivity solvent is shown for selected
solvents in Table I. The solvents listed in this table represent potentially
useful conductivity solvents and displayed good sensitivity and linearity,
with the exception of nitrobenzene which exhibited very poor linearity for
quantities of heptachlor epoxide greater than approximately 25 ng. Very little
or no response was observed for hexadecane for all the solvents investigated.
Consequently, selectivities for heptachlor epoxide versus hexadecane are reported
as being greater than the selectivity that would be calculated if the hexdecane
response was twice that of the noise level. Thus, Table I does not imply that
the use of ethyl alcohol as the conductivity solvent will result in greater
selectivity for halogen-containing compounds relative to hydrocarbons than will
any of the other solvents.
Since the conducting species created from caffeine and parathion are not
known, selectivities were calculated based upon the response in peak height
per gram of substance. These values therefore do not represent absolute
selectivities and should not be compared with data from other studies unless
specifically stated.
It can be seen from the data in Table I that hydrocarbons will give very
little interference in the determination of chlorine-containing compounds.
However, certain other compounds can give a significant response that is not
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10
Table I. Relative Selectivity for Halogen-Containing Compounds versus
Various Types of Compounds as a Function of the Conductivity
Solvent.3jD
Solvent
50% EtOH
EtOH
i-PrOH
Nitrobenzene
Acetonitrile
n'C16H34
>42,000
>79,000
>34,500
>32,000
> 5,500
Caffeine
26
51
62
400
4
Parathion
18
43
111
640
9
Ethyl Stearate
54
161
173
>1600
28
aQuartz reaction tube was 2 mm. i.d., furnance temperature was 950°,
and the hydrogen reaction gas flow rate was 5 cc/min.
Selectivities were calculated from peak heights per gram of substance.
°The ion exchange resin tube was packed with 50% Amberlite IRN-150 (cell side)
and 50% Amber!ite IRN-77 (pump side).
-------
11
greatly influenced by most of the conductivity solvents investigated. (See
Figure 4). Solvents such as nitrobenzene and nitroethane can increase the
selectivity for halogen-containing compounds. These solvents, however, display
very poor linearity of response and are not practical to use.
In general, absolute alcohols give the best performance for the determination
of halogen compounds. They are compatible with the ion exchange resin, give
good sensitivity and provide a wide linear dynamic range. Selectivity, although
good against hydrocarbons, may not be sufficient for certain other types of
compounds, and as shown in Table I, selectivity can be as low as 10 to 100.
In an effort to enhance selectivity, the effects of reaction gas flow
rate and furnace temperature are investigated. A 1:1 ethyl alcohol/water
conductivity solvent was used so that the response from any weak acids or
bases (i.e. C02, NH-) would not be leveled and the influence of the reaction
conditions more readily seen.
Detector responses to heptachlor epoxide and a variety of non-halogen
compounds as a function of furnace temperature and hydrogen reaction gas flow
rate are shown in Tables II-IV. Since there are a number of variables such
as condition of the reaction tube, the cleanliness of the Teflon transfer line
and the occurance of ion exchange resin bleed which can influence detector response,
the data in these tables should only be used for qualitative comparisons and
the determination of response trends.
Response to heptachlor epoxide increases with an increase in furnace
temperature and is approximately three times as large at 950° as at 700°. Caffeine
also displays a similar but more positive temperature relationship. Response to
ethyl stearate increases with temperature to a maximum at 875° and then decreases
-------
>
E
B
e
a
to
K
O-
0
2
Time (min.)
Figure 4. Chromatograms of the selectivity mixture with different conductivity
solvents. Conditions: furnace temperature, 950°; H2 reaction gas,
5 cc/min; conductivity solvent; A = acetonitrile, B = nitrobenzene,
C = methyl alcohol.
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13
Table II. Influence of Furnace Temperature on Detector
Response in the Pyrolytic Mode Using No Reaction Gasc
Furnace Temperature (°C)
Compound
Hept. Epox.
Parathion
Caffeine
Ethyl Stearate
Hexadecane
Thioanisole
N_, N-di ethyl -p-
anisidine
700
970
50
NDb
ND
ND
13
6
750
970
70
ND
6
ND
27
3
800
1170
96
5
25
ND
50
2
825
1170
92
11
54
ND
65
2
850
1680
132
23
90
ND
71
2
875
1850
132
50
97
ND
73
3
900
2180
139
50
97
ND
53
3
925
2110
114
52
72
ND
50
3
950
2560
114
66
57
ND
49
3
Response is in mho-sec/gram. The conductivity solvent was 1:1 EtOH/hLO
at a flow rate of 0.5 cc/min.
ND = No response detected.
-------
14
Table III. Influence of Furnance Temperature on Detector Response
in the Pyrolytic Mode Using 5 cc/min Hydrogen Reaction Gas ,
Furnace
Compound
Hept.- Epox.,
Parathion
Caffeine
Ethyl Stearate
Hexadecane
700
630
22
NDb
ND
ND
750
810
37
2
10
ND
800
840
42
7
40
ND
825
1180
44
10
87
ND
Temperature (°C)
850
1390
38
24
121
0.01
875
1520
29
27
124
0.01
900
1910
24
36
100
ND
925
2020
23
38
71
ND
950
2740
27
46
47
ND
aResponse is in mho-sec/gram. The conductivity solvent was 1:1 EtOH/HpO
at a flow rate of 0.5 cc/min.
ND =: No response detected.
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15
Table IV. Influence of Furnace Temperature on Detector Response in
the Pyrolytic Mode Using 50 cc/min. Hydrogen Reaction Gasc
Furnace Temperature (°C)
Compound
Hept. Epox.
Parathion
Caffeine
Ethyl Stearate
Hexadecane
Thioanisole
N.,N-d1 ethyl -p_-
anisidine
700
710
32
NDb
ND
ND
9
5
750
1080
27
ND
2
0.01
28
8
800
1120
27
ND
39
0.01
49
10
825
1120
23
ND
74
0.02
58
12
850
1120
25
5
133
0.02
58
10
875
960
21
13
142
0.02
55
10
900
1050
17
20
121
0.02
54
9
925
1340
15
30
98
0.02
54
10
950
2140
20
37
76
0.02
50
7
Response is in mho-sec/gram. The conductivity solvent was 1:1 EtOH/h^O
at a flow rate of 0.5 cc/min.
ND =: No response detected.
-------
16
to approximately 50% of the maximum value. Although parathion and thioanisole
represent different classes of sulfur compounds, they exhibit similar temperature
trends. In the absence of hydrogen reaction gas, they reach a maximum positive
response between 850 to 900°, whereas in the presence of reaction gas they exhibit
a slight negative temperature relationship from 800 to 950°.
Although the presence of hydrogen reaction gas slightly alters the
temperature relationships for some of the compounds, particularly the sul-
fur-containing compounds, selectivity to heptachlor epoxide is not signifi-
cantly increased (See Tables V-VII). In fact, selectivity is slightly
decreased by the presence of hydrogen reaction gas for ethyl stearate, thioanisole
and N_, N-diethyl-p_-anisidine. Representative chromatograms for the selectivity
mixture are shown in Figure 5 and 6.
The data in Tables V-VII indicate that selectivity to halogen compounds
may be greater at temperatures in excess of 950 since the selectivity values
increase for all compounds from 900 to 950°. Thus, a high temperature furnace
was constructed so that this potential increase in selectivity could be
investigated. The furnace had a heated zone of approximately 1 inch and
employed a platinum-10% rhodium heating element which was encased in Transite
insulation (0.75 in. thick). Furnace temperatures were determined from an applied
voltage-temperature curve.
Results obtained with this furnace operated at 1100° and a hydrogen reaction
gas flow rate of 5 cc/min. are summarized in Table VIII. Under these conditions,
100 ng of ethyl stearate produces no visible response, and selectivity is
3
> 10 (calculated using a value of 2 mho-sec/gram). Selectivity versus parathion
and caffeine is also improved and increases from methyl to isopropyl alcohol
as the conductivity solvent (See Figure 7). Selectivity to heptachlor epoxide
can be further improved by increasing the hydrogen flow rate (See Figure 8).
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Table V. Influence of Furnace Temperature on Specificity of Response to Heptachlor
Epoxide Relative to Various Compounds in the Pyrolytic Mode Using no
Reaction Gasa.
Furnace Temperature
Compound
Hept. Epox.
Parathion
Caffeine
Ethyl Stearate
Hexadecane
Thioanisole
N_, N.-di ethyl -£-
anisidine
700
1
19
>940
>320
>97,000
75
162
750
1
14
>940
162
>97,000
36
323
800
1
12
234
47
>117,000
23
585
825
1
13
106
23
>117,000
18
585
850
1
13
73
19
>168,000
24
840
875
1
14
37
19
>185,000
25
617
900
1
16
44
22
>218,000
41
727
925
1
19
41
29
>21 1,000
42
703
950
1
22
39
45
>256,000
52
853
aThe conductivity solvent was 1:1 EtOH/H20
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Table VI. Influence of Furnace Temperature on Specificity of Response to Heptachlor
Epoxide Relative to Various Compounds in the Pyrolytic Mode Using 5 cc/min
of Hydrogen Reaction Gasa.
Furnace Temperature
Compound
Hept. Epox.
Parathion
Caffeine
Ethyl Stearate
Hexadecane
700
1
29
>405
>400
>63,000
750
1
22
405
81
>81 ,000
800
1
20
120
21
> 84 ,000
825
1
27
118
14
>118,000
850
1
37
58
11
139,000
875
1
52
56
12
152,000
900
1
80
53
19
>191,000
925
1
88
53
28
>202,000
950
1
101
60
58
>274,000
aThe conductivity solvent was 1:1 EtOH/H20
00
-------
Table VII. Influence of Furnace Temperature on Specificity of Response to Heptachlor
Epoxide Relative to Various Compounds in the Pyrolytic Mode Using 50 cc/min
of Hydrogen Reaction Gasa.
Furnace Temperature (°C)
Compounds
Hept. Epox.
Parathion
Caffeine
Ethyl Stearate
Hexadecane
Thioanisole
JWJ.-d1ethyl-fi.-
anisidine
700
1
22
>355
>355
>71,000
79
142
750
1
40
>540
540
108,000
39
135
800
1
41
>560
29
112,000
23
112
825
1
49
>560
15
56,000
19
93
850
1
45
224
8
56,000
19
112
875
1
46
74
7
48,000
17
96
900
1
62
53
9
52,500
19
117
925
1
89
45
14
67,000
25
134
950
1
107
58
28
107,000
43
306
Response is in mho-sec/gram. The conductivity solvent was 1:1 EtOH/H20 at a flow rate of 0.5 cc/min.
-------
<=>,-
>
E
e
e
a
700'
850°
VJ
950
ro
o
0
2
02
Time (min.)
2
Figure 5. Chromatograms of the selectivity mixture at different furnace
temperatures. Conditions: \\2 reaction gas, 0 cc/min; conductivity
solvent, 50% ethyl alcohol; resin, ARM-381; attenuation, 3 X 0.8.
-------
>
E
c
e
a
«
0
K
O-
Q cc/min
i
r
5 cc/min
10 cc/min
o
T
2
T
is
r
Time (min.)
Figure 6. Chromatograms of the selectivity mixture at different H2 reaction
gas flow rates. Conditions: furnace temperature, 800°;
conductivity solvent, 50% ethyl alcohol; attenuation, 3 X 0.4.
-------
22
Table VIII. Influence of Conductivity Solvent on Specificity of Response
to Heptachlor Epoxide Relative to Various Compounds in the
Pyrolytic Mode Using a Furnace Temperature of 1100°C and
5 cc/min of Hydrogen Reaction Gas.
Selectivity3
Solvent
Methyl Alcohol
Ethyl Alcohol
Isopropyl Alcohol
n-C16
>363,000b
>360,000
>140,000
Caffeine
24
38
71
Parathion
138
136
265
Ethyl Stearate
>3,600C
>3,400
>1 ,400
Calculated from response in mho-sec/gram.
Calculated using a lower value of 0.02 mho-sec/gram.
Calculated using a lower value of 2 mho-sec/gram.
-------
e
o
a
O-
B
IV)
CO
0
2
4
024
Time (min.)
Figure 7.
Chromatograms of the selectivity mixture with different conductivity
solvents. Conditions: furnace temperature, 1100°; H2 reaction gas,
5 cc/min; conductivity solvent, A = methyl alcohol, B = ethyl alcohol,
C = isopropyl alcohol; attenuation, 3 X 1.6.
-------
24
9,
e
o
a
o-
Qcc/min
50 ec/mln
0
2
4
Time (min.)
Figure 8. Chromatograms of the selectivity mixture at two different
H2 reaction gas flow rates. Conditions: furnace
temperature, 1100°; conductivity solvent, isopropyl
alcohol; attenuation, 3 X 1.6.
-------
25
As shown in Table IX, selectivity versus parathion is > 835 using isopropyl
alcohol as the conductivity solvent and 50 cc/min. of hydrogen reaction gas.
Selectivity against caffeine, however, is still fairly low.
Although the selectivity and peak shape for heptachlor epoxide (See Figure 8)
are quite good at a furnace temperature of 1100° and 50 cc/min. of hydrogen
reaction gas, the useful life of the quartz reaction tube is only a few days.
Thus, the use of elevated temperatures to gain selectivity is not a practical
solution. The upper temperature limit for the quartz tubing appears to
be 900 to 950°. However, even at this temperature the quartz tube may require
frequent cleaning and conditioning.
The quartz tube can be cleaned by soaking in concentrated hydrofluoric
acid (48%) for approximately 5 min. and rinsing thoroughly with distilled water,
methyl alcohol, acetone and hexane. After drying the tube is then treated
with Sylon CT (Suoelco, Inc.) for approximately 15 min. and then throughly
rinsed with dry toluene followed by methyl alcohol. After this .treatment
the quartz tubing should be deactivated, and chromatograms with little
tailing, similar to that shown in Figure 9, should be readily obtained.
"Reduction of Peak Tailing". Peak tailing is often encountered in the
determination of quantities of chlorine-containing compounds of approximately
10 ng and below. Tailing peaks usually results in poor sensitivity, linearity and
resolution. Thus, it is important that tailing be minimized. Tailing is usually
due to the quartz reaction tube, a dirty Teflon transfer line from the furnace
to the conductivity cell, a dirty conductivity cell or bleed from the ion
exchange resin.
Cleaning the quartz reaction tube with hydrofluoric acid and deactivating
it with Sylon CT as described above usually eliminates most of the tailing
-------
26
Table IX. Influence of Hydrogen Reaction Gas Flow Rate on Specificity
of Response to Heptachlor Epoxide Relative to Various Compounds
in the Pyrolytic Mode Using a Furnace Temperature of 1100°C
and Isopropyl Alcohol as the Conductivity Solvent.
Selectivity9
H£ (cc/min) n~^l6 ^04 Caffeine
0 >108,000b 66
5 >140,000 71
30 >158,000 132
50 > 209, 000 145
Parathion
111
265
>634
>835
Ethyl Stearate
>1 ,030C
>1 ,400
>1,580
>2,090
Calculated from response in mho-sec/gram.
Calculated using a lower value of 0.02 mho-sec/gram.
Calculated using a lower value of 2 mho-sec/gram.
-------
27
>
E
CO
e
o
a
to
o-
i
2
6
Time (min.)
Figure 9. Chromatogram of the pesticide mixture. Conditions:
furnace temperature, 800 ; H2 reaction gas, 5 cc/min;
sample size, 10 ng; conductivity solvent, methyl alcohol;
attenuation, 10 X 1.6.
-------
28
associated with the tube. If tailing due to the reaction tube persists, the
quartz tube should be replaced and the new tube cleaned and deactivated. The
Teflon transfer line can. be cleaned with organic solvents such as chloroform,
acetone and hexane. The transfer line should be interfaced to the quartz
reaction tube with a short piece (0.5 in.) of 1/8-in. o.d. X 1/16-in. i.d.
Teflon tubing. The 1/8-in. tube is fastened to the quartz tube with a 1-in.
piece of 1/8-in i.d. heat shrinkable Teflon tubing. The conductivity cell
can be cleaned by disassembling and "sonicating" with 30-40% phosphoric acid,
followed by distilled water, methyl alcohol, acetone and hexane. Ion exchange
resin bleed can be minimized by soxhlet extracting the resin with water and
then methyl alcohol .for approximately 8 hr. each. Amberlite IRN-150 mixed
H /OH~ resin and Amberlite IRN-77 H resin are the preferred resins. The ion
exchange tube should be packed with 50-67% IRN-77 on the pump side and 33-50%
IRN-150 on the cell side to maintain the proper acidity.
Linearity of Response to Chlorine-Containing Compounds. As shown in
Figure 10, detector response to chlorine-containing compounds is linear over
four to five orders of magnitude. Detector linearity in the low nanogram
range (Figure 11) is very dependent upon the condition of the detector, and if
peak tailing is present, response will not be linear.
Optimization of Detector Operating Conditions for the Selective Detection
of Chlorinated Hydrocarbon Pesticides in the Presence of Polychlorinated Biphenyls
and Polychlorinated Napthalenes. The influences of furnace temperature and hydrogen
reaction gas flow rate on the response to chlorinated hydrocarbon pesticides,
Polychlorinated biphenyls (PCB) and polychlorinated napthalenes (PCN) were investi-
gated using three solutions. One solution contained 10 ng per yl each of lindane
heptachlor, aldrin, heptachlor epoxide and dieldrin. A second solution contained
100 ng per yl of Halowax 1013 and Aroclor 1254. A third solution contained
the chlorinated .pesticides and the PCB and PCN at the same concentration as
-------
29
c
e
a
O)
e
Diazinon
Pa rathion
-9
-8
log grams
Figure 10. Linearity of response todiazinon> andpar^thion. Conditions:
furnace temperature, 700 , H2 reaction gas, 0 cc/min;
conductivity solvent, methyl alcohol; resin, IRN-150/77.
-------
30
o
o.
o
o
o-
00
I °
- s
«D
e
o
a.
o
o
o
o-
es
Heptechlor Epoxidi
Dieldrin
0.2
04 Oj6
Concentration ( ng )
0.8
1.0
Figure 11.
Linearity of response to subnanogran quantities of
heptechlor epoxide and di.eldrin, Conditions: furnace
temperaturej 700°; Ho reaction gas, 10 cc/min; conductivity
solvent, methyl alcoriol; resin, IRN-150/77.
-------
31
in the other solutions. Furnace temperature was varied from 700 to 850° in 25°
increments. Hydrogen reaction gas flow rates were 0, 3 and 10 cc/min.
The results of this study are summarized in Tables X-XII. In the absence
of hydrogen'reaction gas, there is no response from the PCB and PCN at 800°
and below. The addition of hydrogen reaction gas results in a significant
increase in response to the PCB and PCN, and the furnace temperature must be 725°
or below to eliminate interferences from PCB and PCN in the detection of chlorinated
hydrocarbon pesticides. There appears to be little difference in the results
obtained with 3 and 10 cc/min. of reaction gas. There is, however, some advantage
in using reaction gas since the response to the pesticides is a little greater than
without reaction gas, even at "selective" furnace temperatures. Representative
chromatograms of detector response to chlorinated insecticides in the presence
of PCB and PCN at a furnace temperature of 725 and 850° are shown in Figures 12
and 13, respectively.
Evaluation of Nickel Tubing for the Detection of Halogen-Containing
Compounds in the Catalytic Reductive Mode. As previously discussed, specificity
to halogen compounds in the pyrolytic mode is very dependent on detector operating
conditions. However, conditions which give stable detector performance result in
selectivities against certain compounds that may be insufficient for some analyses.
Consequently, the catalytic reductive mode was investigated in an attempt to
improve selectivity to halogen-containing compounds.
In the catalytic reductive mode, reaction products from organic compounds
containing halogen, nitrogen, sulfur and oxygen are HX, NH3, H2S, HpO, CH4
and lower alkanes. Although H20, CH4 and lower alkanes will not give a
response, NH3 and H2$ can give significant responses unless their ionization
•is precluded. Since NH3 is a weak base and H2$ is a weak acid, their ionization
can be leveled by the proper choice of conductivity solvent.
-------
32
Table X. Influence of Furnace Temperature on the Response to Chlorinated
Pesticides, PCB and PCN Using no Hydrogen Reaction Gasa.
Compound
Lindane
Heptachlor
Aldrin
Hept. Epox.
Dieldrin
PCB + PCNC
Peak A
Peak B
Peak C
Peak D
Peak E
Lindane + Peak A
Heptachlor + Peak B
Aldrin + Peak C
Hept. Epox. + Peak D
Dieldrin + Peak E
Furnace
700
40
16
14
23
15
NDd
ND
ND
ND
ND
39
16
12
22
14
725
51
17
15
21
15
ND
ND
ND
ND
ND
62
23.
17
25
18
750
76
28
20
28
19
ND
.ND
ND
ND
ND
67
25
17
24
17
Temperature (°
775
71
33
22
27
19
ND
ND
ND
ND
ND
67
32
20
25
18
800
65
39
27
30
19
ND
ND
ND
ND
ND
74
45
30
32
24
C)
825
73
56
40
38
24
ND
ND
2
ND
2
77
59
42
38
26
850
70
59
46
40
22
ND
ND
5
2
3
60
56
43
37
24
Response is in mm of peak height.
^Quantity is 10 ng for each pesticide and 100 ng for PCB
and 100 rig for PCN.
"Peaks A-E are the detector responses at retention times
equal to lindane-dieldrin, respectively
ND = No response detected.
-------
33
Table XI. Influence of Furnace Temperature on the Response to
Chlorinated Pesticides, PCB and PCN Using 3 cc/min
Hydrogen Reaction Gasa.
Compound
Lindane
Heptachlor
Aldrin
Hept. Epox.
Dieldrin
PCB + PCNC
Peak A
Peak B
Peak C
Peak D
Peak E
Lindane + Peak A
Heptachlor + Peak B
Aldrin + Peak C
Hept. Epox. + Peak D
Dieldrin + Peak E
Furnace
700
42
52
28
52
27
NDd
ND
ND
ND
ND
46
59
30
54
32
725
66
64
32
58
31
ND
ND
ND
ND
ND
61
62
36
56
34
750
86
98
58
83
48
1
ND
7
1
7
83
91
59
78
66
Temperature (°
775
82
104
75
72
43
5
40
57
50
68
89
131
90
107
119
800
89
104
85
80
47
11
46
64
62
84
104
142
102
114
119
C)
825
96
99
82
77
46
22
50
73
67
90
108
131
93
101
115
850
94
76
65
61
32
25
38
55
50
60
128
123
86
93
108
Response is in mm. of peak height.
Quantity is 10 ng for each pesticide and 100 ng for PCB and
100 ng for PCN.
cPeaks A-E are the detector responses at retention times equal to
1indane-dieldrin, respectively.
ND = No response detected.
-------
34
Table XII. Influence of Furnace Temperature on the Response to
Chlorinated Pesticides, PCB and PCN Using 10 cc/min
Hydrogen Reaction Gasa.
Compound
Lindane
Heptachlor
Aldrin
Hept. Epox.
Dieldrin
PCB + PCNC
Peak A
Peak B
Peak C
Peak D
Peak E
Lindane + Peak A
Heptachlor + Peak B
Aldrin + Peak C
Hept. Epox. + Peak D
Dieldrin + Peak E
Furnace
700
37
40
23
39
21
NDd
ND
ND
ND
ND
36
37
26
34
19
725
74
85
45
71
38
ND
ND
ND
ND
ND
80
89
50
71
46
750
71
89
52
73
41
ND
2
ND
ND
ND
82
106
65
83
56
Temperature (°
775
92
107
65
79
44
2
ND
5
ND
4
94
115
74
82
55
800
94
98
78
69
43
19
46
75
47
66
119
160
131
130
134
C)
825
104
87
70
60
37
34
72
90
75
101
142
150
123
126
122
850
123
89
71
65
38
43
91
85
71
90
169
161
133
134
132
Response is in mm. of peak height.
Quantity is 10 ng for each pesticide and 100 ng for PCB
and 100 ng for PCN.
"Peaks A-E are the detector responses at retention times
equal to lindane-dieldrin, respectively.
ND = No response detected.
-------
>
E
o
(a
e
o
a
CO
o
co
en
O-
vj
I
2
Figure 12.
0 i
T ime (min .)
T
Chromatograms of the chlorinated pesticide mixture in the presence
of PCB and PCN. Conditions: furnace temperature, 725°; H2 reaction
gas, 3 cc/min; conductivity solvent, methyl alcohol; A, 10 ng of
chlorinated pesticides; B, A + 100 ng PCB + 100 ng PCN; C, 100 ng
of PCB and 100 ng PCN.
-------
B
>
E
o>
(/)
c
o
Q.
o-
co
CTi
1
4
6
0
2
i
8
r
0
I
2
8
Time (min.)
Figure 13. Chromatograms of the chlorinated pesticide mixture in the presence
of PCB and PCN. Conditions: furnace temperature, 850°; \\2 reaction
gas, 3 cc/min; conductivity solvent, methyl alcohol; A, 10 ng
of the pesticide mixture; B, A + 100 ng PCB + 100 ng PCN;
C, 100 ng PCB and 100 ng PCN.
-------
37
Nickel tubing was chosen instead of a quartz tube packed with a nickel
catalyst because it will not break and is free of polar absorption sites. Nickel
tubing 1/8 in. o.d. X 0.08 in. i.d. and 1/16 in. o.d. X 0.02 in. i.d. were
evaluated. The large tubing did not give adequate reduction, but the small
tubing was very effective.
The influences of furnace temperature, hydrogen reaction gas flow rate
and conductivity solvent on detector sensitivity, linearity and selectivity
to halogen-containing compounds were investigated using a 1/16-in. o.d. X 0.02-in.
i.d. X 5.0-in. nickel reaction tube. A 1/8-in. to 1/16-in. Vespel reducing
ferrule was used to connect the reaction tube to the furnace, and the Teflon
transfer tube was connected to the reaction tube with a 3/16-in. o.d. X 1/16-in.
i.d. X 3/8-in. Vespel tube.
As shown in Figure 14, detector response to the selectivity mixture is
fairly independent of furnace temperature over a range of approximately 100°.
This indicates that the nickel reaction tube gives complete reduction of the
compounds from 850 to 950°. It can also be seen that there is no response
from ethyl stearate, which indicates that the ester function has been effectively
reduced. Although there is no response to hexadecane and ethyl stearate with
methyl alcohol as the conductivity solvent, response is greater for caffeine
than that obtained using quartz tubing, and response to parathion is approximately
the same.
In contrast to quartz tubing, however, the response to non-halogen compounds
can be greatly reduced by using a longer chained alcohol as the conductivity solvent.
The influence of conductivity solvent on response to the selectivity mixture
is shown in Figure 15. As can be seen in this figure, the use of ethyl
alcohol results in small negative responses for caffeine and parathion instead
of the large positive responses observed with methyl alcohol. The degree of the
-------
>
E
u>
M
C
o
Q.
M
750*
850
Hept. Epox.
—IT
950
-—]Lr
GO
2
4
0
2
Time (min.)
Figure 14. Chromatograms of the selectivity mixture with a nickel reaction
tube at different furnace temperatures. Conditions: \\2 reaction
gas, 80 cc/min; conductivity solvent, methyl alcohol; attenuation,
1 X 6.4.
-------
39
>
E
0)
(0
c
o
Q.
in
0)
CC
o-
B
A 2 4
T i me (m i n.)
Figure 15. Chromatograms of the selectivity mixture with a nickel
reaction tube and different conductivity solvents.
"---•-• ••-- furnace temperature, 850°- " J-'~
Conditions:
gas 100 cc/min;
B = n-butyl alcohol
H2 reaction
conductivity solvent; A = methyl alcohol,
attenuation, A = 1 X 6.4, B = 1 X 1.6.
-------
40
negative response is decreased by the use of ji-propyl alcohol and essentially
eliminated with jn-butyl alcohol.
The negative response for nitrogen-containing compounds is a result of
decreasing the conductivity of the solvent by replacing the larger specific
conductance of the proton with that of the ammonium ion. Consequently, the
degree of negative response will depend upon the amount of bleed from the ion
exchange resin (H form), the quantity of ammonia produced and the ionizing
properties; of the conductivity solvent. The degree of negative response should
decrease with time since ion exchange resin bleed decreases.
The effect of reaction conditions on detector sensitivity and specificity
to chlorine-containing compounds is shown in Tables XIII and XIV. Detector
response (with 40 cc/min helium carrier gas) increases with hydrogen reaction gas
flow rate up to 60 cc/min. Response is approximately the same for flow rates
of 60 and 100 cc/min. (Table XIII).
Detector specificity to chlorine containing compounds versus nitrogen-,
sulfur- arid ester-containing compounds as a function of furnace temperature was
determined with m-chlorotoluene (10 ng), m-tolunitrile (10 yg), thioanisole
(10 yg) and methyl o-toluate (10 yg). Detector selectivity for chlorine versus
nitrogen increases with furnace temperature from 800 to 900 , and reaches a
value of 4,300 at 900° (See Table XIV). However, selectivity to chlorine
versus sulfur or esters reaches a maximum at 870°, and is 9,500 and 95,600
against sulfur and esters, respectively.
The influence of furnace temperature and conductivity solvent on the response
to non-halogen compounds was also investigated using the selectivity mixture
employed in the pyrolytic mode studies. The results of this study are
summarized in Table XV. As indicated by Figure 15, selectivity for heptachlor
epoxide versus caffeine and parathion is very poor with methyl alcohol as the
conductivity solvent, but is good with rHDUtyl alcohol.
-------
41
Table XIII. Influence of Hydrogen Reaction Gas Flow Rate on Detector
Response to Chlorinated pesticides in the Catalytic
Reductive Mode with a Nickel Reaction Tube3*".
Flow
-
Rate (cc/min)
20
30
60
100
Peak Height jmm)
Lindane
39
50
76
78
Hept.
42
55
53
50
Aldrin
32
39
40
40
Hept. Epox.
28
38
39
36
Dieldrin
17
20
22
23
aFurnace temperature was 840°; conductivity solvent was ji-butyl
alcohol.
Sample size was 1 ng.
-------
42
Table XIV. Influence of Furnace Temperature on
Detector Specificity to Chlorine
Relative to Nitrogen, Sulfur and Esters
in the Catalytic Reductive Mode with
a Nickel Reaction Tubea>b
Furnace Temperature
800
870
900
N
1,920
3,360
4,300
Element
S
9,870
9,500
5,020
-0-^=0
32,020
95,600
42 ,400
aReaction gas flow rate was 100 cc/min of hydrogen;
conductivity solvent was j^-butyl alcohol.
Selectivities were calculated from peak areas using
m-chlorotoluene (10 ng), rn-tolunitrile (10 yg),
thioanisole (10 yg) and methyl £-toluate (10 yg).
-------
43
Table XV. Influence of Conductivity Solvent and Furnace Temperature
on Selectivity to Chlorine in the Catalytic Reductive
Mode9.
Selectivity
Conductivity
Solvent
MeOH
EtOH
n-PrOH
n-BuOH
Furnace
Temperature
700
750
800
850
900
950
700
750
800
850
900
950
800
850
900
950
750
800
850
900
950
n-C16
NDb
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
Caffeine
6
8
4
1
1
1
8
188r
NRC
NR
NR
NR
NR
NR
247
288
NR
NR
NR
NR
NR
Parathion
11
20
36
8
4
4
17
57
2,225
NR
NR
NR
NR
NR
NR
NR
NR
NR
NR
NR
NR
Ethyl
Myri state
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
aHydrogen reaction gas flow rate was 100 cc/min.
ND = No response detected.
£
NR = Negative response.
-------
44
Linearity of detector response to chlorine-containing pesticides with a
nickel reaction tube is shown in Figure 16. Response is linear from 0.1 ng to
1 pp. Linearity of response for sample quantities below apprixmately 25 ng de-
pends upon the condition of the nickel tube. New tubes must be conditioned for several
days before they exhibit good linearity and peak shape, but once conditioned last
for six months or more. Contaminants in the helium carrier gas also contribute
to non-linear response and poor peak shape. Contamination was present in
approximately two out of every three tanks of helium, and for this reason
electrolytic hydrogen was used for both the carrier and reaction gas for most
applications.
Minimum Detectable Quantity. The minimum detectable quantity, defined as that
quantity of material required to give a response twice that of background, depends
upon the same factors that influence peak shape and linearity. It also depends
upon furnace temperature and conductivity solvent. Although detector response
is greater for aqueous conductivity solvents, the signal-to-noise ratio is
greater for absolute alcohols. Thus, the minimum detectable level is less for
absolute alcohols than for the 1:1 isopropyl alcohol/water conductivity solvent
recommended by the manufacturer. In general, minimum detectable levels of
20-50 pg are usually obtained for the common chlorinated hydrocarbon pesticides
at retention times of five minutes or less. The minimum detectable quantities
for representative chlorinated pesticides analyzed at different operating
conditions are listed in Table XVI. Representative chromatograms of low
levels of pesticides are displayed in Figure 17.
-------
45
o
(0
c
o
a
CO
fl)
0)
o
-10
Figure 16.
Iog g rams
Linearity of response to lindane with a nickel reaction
tube. Conditions: furnace temperature, 840 ; Ho reaction
gas, 100 cc/min; conductivity solvent, methyl alcohol;
resin, IRN-150/77.
-------
46
Table XVI. Minimum Detectable Quantities of Halogen-Containing Compounds3,
Conditions
Nitrobenzene
2/3 IRN-150 + 1/3 IRN-77
FT = 950°, H2 == 5 cc
2 mm id. quartz tube
25% Isopropyl alcohol
IRN-150
FT = 850°, H2 = 3 cc
2 mm ijd. quart;: tube
Methyl alcohol
2/3 IRN-150 + 1/3 IRN-77
FT = 700°, H2 - 10 cc
2 mm i .d. quartz tube
Methyl alcohol
2/3 IRN-150 + 1/3 IRN-77
FT = 860°, Hp := 140 cc
Nickel tube
n-Butyl alcohol
2/3 IRN-150 + 1/3 IRN-77
FT - 860°, tty ••-- 140 cc
Nickel tube
Lindane
14pg
(0.88)b
17pg
(1.04)
22pq
(0.80)
11 pg
(1.04)
63pg
(1.12)
Heptachlor
17pg
(1.48)
25pg
(1.76)
25pg
(1.32)
I7pg
(1.64)
83pg
(1.88)
Compound
Aldrin
19pq
(1.84)
33pg
(2.24)
33pg
(1.60)
17pq
(2.08)
lOOpg
(2.32)
'
Hept. Epox.
n pg
(2.24)
33pg
(2.72)
29pg
(1.96)
18pq
(2.52)
83pg
(2.80)
Dieldrin
13
(3.20)
40pg
(4.00)
44pg
(2.80)
27pq
(3.64)
111
(4.08)
aMinimum detectable quantities are that 2x noise and short-term drift.
Values in parenthesis are retention times in minutes.
-------
47
3-
>
E
0)
05
c
o
Q.
(O
0)
QC
o-
B
2
6 2
T i me (min.)
Figure 17. Chromatograms of low levels of the chlorinated pesticide
mixture with a nickel reaction tube. Conditions: furnace
temperature, 850°; H2 reaction gas, 100 cc/min;
conductivity solvent, methyl alcohol; sample quantity,
A = 0.1 ng of each compound, B = 0.25 ng of each compound;
attenuation, A = 1 X 0.2, B = 1 X 0.4.
-------
48
Detection of Sulfur-Containing Compounds
Optimization of Detector Operating Conditions. Sulfur-containing compounds
are detected as the strong acids H^SO, and HUSO, which are formed from the
combustion products SCL and SCL. Organic sulfur-containing compounds can be
converted to S(L and S(L by oxidative pyrolysis or catalytic oxidation. The
formation of SCu is favored at moderate furnace temperatures, whereas S02 is
favored at higher temperatures. However, since both S02 and SCu are converted
to the strong acids HpS03 and HUSO, upon contact with water, the relative
quantities of these sulfur species is of little importance. Quartz reaction
tubes are used for the pyrolytic oxidation of sulfur compounds, and either
nickel reaction tubes or quartz tubes with an oxidation catalyst are used for
the catalytic oxidation mode. Oxygen or air can be used for the reaction gas.
"Conductivity Solvent and -Reaction Systems" Detector sensitivity and
specificity to sulfur-containing compounds are'dramatically influenced by
contact material (or catalyst), type and pH of the conductivity solvent,
and reaction gas flow rate. The specific detection of sulfur compounds is
complicated by interferences from all carbon-containing compounds since the
detection of organic carbon has the same general requirements as the detection
of sulfur. In the oxidative mode, organic carbon is converted to C02 and upon
contact with water C02 forms the weak acid H,,C03. Thus, optimization of detector
operating conditions are extremely important, and the greater ease of oxidation
of sulfur compounds and the strong acidity of H2S03 and H2$04 must be taken to
full advantage.
The influence of detector operating conditions was investigated using
diazinon and parathion as probe sulfur compounds. Specificity to sulfur was
determined relative to hydrocarbons (j^-hexadecane) and esters (ethyl myristate)
-------
49
as the response in peak height per gram of sulfur divided by the response in
peak height per gram of hydrocarbon or ester.
The influence of furnace temperature on detector specificity was studied
from 600 to 950 using 1-mm and 2-mm i.d. quartz reaction tubes with and without
contact materials. In general, there was little difference in specificity
between the two sizes of tubes. However, the small i.d. tube was very resistant
to contamination, whereas the larger tube exhibited a slight tendency to become
contaminated when operated at the lower furnace temperatures. Platinum wire,
copper wire, nickel wire, gold wire, Nichrome wire, Chromosorb W, quartz
chips and quartz wool were evaluated as contact materials.
The influence of furnace temperature on detector response to sulfur-containing
pesticides depends upon whether an empty quartz tube or a quartz tube with
a contact material is used. In general, response increases with furnace
temperature up to a given temperature, and may in some instances reach a plateau
or decrease with a further increase in temperature (See Tables XVII and XVIII).
With an empty quartz reaction tube, response usually continues to increase with
furnace temperature over the range 700 to 950° with conductivity solvents containing
a considerable quantity of water (compare 50 and 100% isopropyl alcohol in
Table XVII). However, if the conductivity solvent does not contain sufficient
water, response usually reaches a maximum at 850 to 900°. This response-temperature
relationship is also observed for quartz reaction tubes containing a quartz wool
contact material. However, as shown in Figure 18, response with a quartz
wool contact material is a complex function of furnace temperature. Response
with a platinum catalyst reaches a maximum at approximately 700 and decreases
with a further increase in temperature (See Table XVIII).
-------
50
Table XVII. Influence of Furnace Temperature on Detector
Response to Sulfur Compounds Using an Empty
Quartz Reaction Tube and Various Conductivity
Solventsa'b.
Conductivity
Furnace Temperature ( C)
Solvent
25% i-PrOH
50% i-PrOH
75% 1-PrOH
100% 1-PrOH
Compound
diazinon
parathion
diazinon
parathion
diazinon
parathion
diazinon
parathion
700
10
10
10
10
10
10
10
10
750
14
13
26
28
14
12
13
12
800
19
15
55
33
25
18
18
14
850
27
17
80
36
36
19
21
15
900
35
21
99
45
41
21
21
15
950
40
24
102
53
39
21
19
15
Reaction tube was 2 mm i.d.; reaction gas = 4 cc/min 0?.
Response = relative peal
assigned a value of 10.
Response = relative peak height with response at 700°
-------
51
Table XVIII. Influence of Furnace Temperature on Detector Response to
Sulfur Compounds Using a Platinum Catalyst and Various
Conductivity Solvents°»b.
Conductivity
Solvent
MeOH
EtOH
i-PrOH
Furnace Temperature (°C)
Compound
diazinon
parathion
diazinon
parathion
diazinon
parathion
575
10
10
10
10
10
10
600
17
14
13
13
12
12
650
19
16
24
19
18
15
700
17
18
27
23
19
16
750
16
16
25
22
17
16
800
15
14
24
23
17
16
850
14
14
21
21
14
14
900
18
17
21
21
14
14
Reaction tube was 1 mm i.d. and contained 1 cm of #35 platinum
wire; reaction gas = 4 cc/min 02-
DRespons;e = relative peak height with response at 575 assigned a
value of 10.
-------
52
Diazino n
Parathion
55O
65O
75O
8SO
05O
Furnace Temp. (°C)
Figure 18.
Detector response to diazinon and parathion as a function
of furnace temperature. Conditions: 1-mm i.d. quartz
reaction tube packed with 0.25 in. of quartz wool;
conductivity solvent, methyl alcohol.
-------
53
The decrease in response with temperature after reaching a maximum
perhaps can be explained by the temperature dependence of the SO,,;SO-
' L. *J
ratio and possible differences in solubilities under the conditions of
operation. This relationship,however, exhibits considerable variability.
It changes slightly with time and is not highly consistent with different
reaction tubes. Therefore, response should be optimized periodically.
Platinum and quartz wool proved to be the only useful contact materials.
The other materials investigated either resulted in poor sensitivity, peak tailing
or excessive detector background noise. Detector specificity to sulfur versus
hydrocarbons and esters as a function of furnace temperature for an empty
reaction tube, reaction tube with quartz wool contact material and reaction tube
with platinum catalyst is exhibted in Tables XIX-XXI, respectively.
As shown by the data displayed in Tables XIX-XXII, conditions for
maximum selectivity do not necessarily coincide with those for maximum
sensitivity. With an empty quartz reaction tube, selectivity versus hydro-
carbons and esters decreases with temperature to a minimum at 800 and then
increases with a further increase in temperature (See Table XIX). Selectivity
relative to hydrocarbons is maximum at 700°, whereas selectivity relative to
esters is maximum at 950°. Selectivity as a function of furnace temperature is
similar with quartz wool as a contact material as that displayed with an empty
tube (See Table XX). Again, selectivity reaches a minimum, but at a slightly
lower temperature (750 ), and then increases- Selectivity is also greater
relative to esters than hydrocarbons at high furnace temperatures. In contrast
to an empty tube, selectivity relative to esters is maximum at the low
furnace temperature, as found for hydrocarbons in both cases. Selectivity
with a platinum catalyst also reaches a minimum, which is at 900 . Comparison
of Figures 19 and 20 demonstrate the importance of furnace temperature for
extremes in operating conditions.
-------
54
Table XIX. Selectivity of the HECD to Sulfur Compounds
Relative to Hydrocarbons Using 75% Isopropanol
as the Conductivity Solvent3
Furnace Temperature
700
750
800
850
900
950
Selectivity
Hydrocarbons
37,200
10,000
480
1 ,080
3,720
12,600
Esters
4,800
600
440
1,320
3,720
24,400
aReaction tube was empty and 2 mm I.D.
-------
55
Table XX. Influence of Furnace Temperature on the
Selectivity of the HECD to Sulfur Compounds
Using Quartz Wool as a Contact Material3.
Furnace Temperature
550
600
650
700
750
800
850
900
950
Selecti
Hydrocarbon
> 83,000
>386,000
436 ,000
214,450
56,720
94,600
40,250
37,700
23,100
vity
Ester
> 83,000
> 386, 000
72,600
57,000
15,810
24,100
49,500
62,300
40,250
aReaction tube was 1 mm I.D.; Conductivity solvent was
methyl alcohol.
-------
56
Table XXI. Selectivity of the HECD to Sulfur Compounds Using
a Platinum Catalyst and Various Concentrations of
Isopropanol as the Conductivity Solvent.
Furnace Temperature %Isopropanol
700 10
75U
800
850
900
950
725 75
800
725 90
800
725 100
800
Selectivi
Hydrocarbon
9,200
6,900
2,600
1,920
840
1,100
7,600
6,520
8,200
7,125
23,320
17,200
ty
Ester
7,500
6,800
4,480
3,440
1,020
2,220
10,800
8,400
12,560
11,360
22,000
15,600
-------
57
00
6-
>
E
o>
(0
c
o
a
(0
a>
cc
B
O-
T
T
Time (m in.)
Figure 19.
Chromatograms of sulfur pesticides and hydrocarbons
with a quartz reaction tube packed with quartz wool.
Conditions: furnace temperature, 650°; conductivity
solvent, methyl alcohol; 02 reaction gas, 4 cc/min;
sample, A = 5 ng of diazinon and parathion
of the hydrocarbons (Clg, C18> Clg and C21
B
-------
58
>
E
W
C
o
a
cc
B
0
2
Figure 20.
Time ( m in.)
Chromatograms of sulfur pesticides and hydrocarbons
with a quartz reaction tube packed with quartz wool.
Conditions: furnace temperature, 900°; conductivity
solvent, methyl alcohol; 02 reaction gas, 4 cc/min;
sample, A = 5 ng of diazinon and parathion. B = 2 yg
of the hydrocarbons (Clg, Clg, Clg and C21).
-------
59
The effectsof different concentrations of water in the conductivity solvent
on selectivity to sulfur relative to hydrocarbons and esters using an empty
quartz reaction tube and a reaction tube containing a platinum catalyst are
shown in Figures 21 and 22. The preseroe of 25% water in the isopropyl alcohol
conductivity solvent greatly decreases the selectivity obtained with an empty
reaction tube. Increase in the quantity of water above 25% has little addi-
tional effect. Selectivity obtained with a platinum catalyst is also decreased
by the addition of water to the conductivity solvent. The selectivity obtained
with the platinum catalyst is fairly low, however; and the effect of water is not
as great.
The flow rate of reaction gas is an important factor. Selectivity to
sulfur relative to hydrocarbons as a function of oxygen flow rate and furnace
temperature is tabulated in Table XXII. Flow rates of 2-5 cc/min. gave a
large solvent response, whereas flow rates lower than approximately 2 cc/min.
gave diminished response to sulfur compounds and resulted in elevated noise
levels. The selectivity-furnace temperature trend, previously discussed, is
slightly altered by reaction gas flow rate. With a reaction gas flow rate of
2 cc/min. selectivity is greater at 700Q than 950°, as is also the case
for the reaction conditions described in Table XIX. This relationship is
reversed at higher reaction gas flow rates.
Although the greatest selectivities to sulfur relative to hydrocarbons and
esters are achieved with a 1-mm quartz reaction tube packed with approximately
0.25 in. of quartz wool, detector response and selectivity deteriorates after
approximately a week of use. The same is also true for a platinum catalyst.
Attempts to recondition the quartz wool and platinum catalyst by rinsing the
reaction tube with organic solvents and/or hydrofluoric acid were not
successful. Thus, for optimum performance the quartz wool should be replaced
periodically. Since significantly higher selectivities are obtained with
-------
60
o
o
o
o"
o
N
o
o
o
o
in
Esters
Hydrocarbons
r
50
T
75
100
Percent Water in Isopropanol
Figure 21. Selectivity to sulfur relative to esters and hydrocarbons
versus water content of the conductivity solvent.
Conditions: quartz reaction tube; furnace temperature,
950°.
-------
61
o
o
o
o
M
Esters
Hyd roca rbons
25 50 75
Percent Water in Isopropanol
Figure 22.
Selectivity to sulfur relative to esters and hydrocarbons
versus water content of the conductivity solvent.
Conditions: quartz reaction tube with platinum catalyst;
furnace temperature, 800 •
-------
62
Table XXII. Influence of Oxygen Reaction Gas Flow Rate
on the Selectivity of the HECD to Sulfur
Compounds Using 95% Ethanol as the
Conductivity Solvent .
Furnace Temperature
700
750
800
850
900
950
2 cc/min
64,800
4,320
2,120
6,920
14,480
13,080
Oxygen Flow Rate
10 cc/min
9,900
4,670
1,570
2,230
3,700
24,550
30 cc/min
17,380
13,220
2,550
1,930
8,530
34,580
Reaction tube was empty and 2 mm I.D.
Note: Noise level increased with oxygen flow rate and
usable sensitivity was less.
-------
63
quartz wool than with empty reaction tubes and peak shape is excellent (See
Figure 23), the little time that it takes to repack the reaction tube is well
spent.
"Reduction of Peak Tailing". Sulfur-containing compounds are not as
prone to exhibit peak tailing as chlorine-containing compounds. Nevertheless,
peak tailing can occur for small quantities of compound (<_ 10 ng) if the
conductivity solvent is not acidic enough or the contact material needs replacing.
Use of polar solvent such as methyl alcohol or 75% isopropyl alcohol,
periodic replacement of the contact material and application of the techniques
developed for the reduction of peak tailing of halogen compounds usually
prevent any peak tailing in the analysis of sulfur-containing compounds; and
chromatograms similar to those shown in Figures 24-28 should be readily obtained.
Linearity of Detector Response to Sulfur-Containing Compounds. As dis-
played in Figure 29-31, detector response to sulfur compounds with a polar
conductivity solvent is linear over approximately two to four orders of
magnitude. The linear dynamic range is very dependent upon the polarity and/or
water content of the conductivity solvent. The influence of water content in the
conductivity solvent is shown in Figures 32-34. Comparison of these figures reveals
that: response to diazinon and parathion is linear from 2X10 g to 1 X 10 g
for 10% isopropyl alcohol, but is non-linear at the upper concentration range
for 90 and 100% isopropyl alcohol. Linearity at the upper range is better with
75% isopropyl alcohol (Figure 29), but is not as good as with 10% isopropyl
alcohol.
Although water is required for the formation of H^SO- and HLSO. from S02
and SOo, one microgram of parathion yields only approximately 2 X 10 g to
3 X 10 g of S02 and SO.,, which under the conditions of operation requires
-------
64
tn
6"
>
E
o
a
CO
0)
QC
6 2 4
Time (mi n.)
Figure 23. Chromatogram of diazinon and parathion. Conditions:
furnace temperature, 700°, reaction tube, 1-mm. i.d.
with quartz wool contact material; 62 reaction gas,
4 cc/min; conductivity solvent, methyl alcohol;
sample size, 5 ng.
-------
>
E
0)
c
o
a
0)
oc
B
tn
2 4
6 i 4
Time (m in.)
6 f
Figure 24.
Chromatograms of diazinon and parathion with a platinum
catalyst. Conditions; furnace temperature, 725°; 02
reaction gas, 4 cc/min; conductivity solvent, 10% .isopropyl
alcohol; sample size, A = 1 ng, B = 10 ng, C = 100 ng;
attenuation, A = 10 X 0.4, B = 10 X 3.2, C = 100 X 3.2.
-------
>
E
o>
-------
>
E
0)
(0
c
o
a
(0
o>
oc
B
0
o i 4
Time (min.)
6 i
Figure 26.
Chromatograms of diazinon and parathion with a platinum catalyst.
Conditions: furnace temperature, 800°, 0? reaction gas, 4 cc/min;
conductivity solvent, 100% isopropyl alcohol; sample size,
A = 2 ng, B = 10 ng, C = 100 ng; attenuation, A = 1 X 0.4,
B = 1 X 1.6, C = 10 X 0.8.
-------
o
(0
c
o
a
10
a
B
00
2
2
Figure 27.
Time (m i n .)
Chromatograms of diazinon and parathion with an empty
quartz reaction tube. Conditions: furnace temperature,
900°; Op reaction gas, 5 cc/min; conductivity solvent,
50% isopropyl alcohol; sample size, A = 1 ng, B = 10 ng,
C = 100 ng; attenuation, A = 10 X 0.4, B = 10 X 1.6,
C = 10 X 12.8.
-------
>
E
0
0>
c
o
Q.
co
tt)
K
B
yii
A I 4 6 i I 6 i
Time (min.)
Figure 28. Chromatograms of diazinon, methyl parathion and parathion
with an empty quartz reaction tube. Conditions: furnace
temperature, 850°; air reaction gas, 20 cc/min; conductivity
solvent, methyl alcohol; sample size, A = 2.5 ng, B = 25 ng,
C = 250 ng; attenuation, A = 1 X 1.6, B = 10 X 1.6, C = 100 X 1.6.
-------
70
e
a
nen
arathlon
y
•0
•8
(09 grain*
I
•6
Figure 29.
Linearity of response to diazinon and parathion.
Conditions: reaction tube, 2-mm. i.d.; furnace
temperature, 900 ; 03 reaction gas, 4 cc/min;
conductivity solvent, 75% isopropyl alcohol.
-------
71
n -
e
o
a
9
O
Diazlnon
Parathlon
•10
I
• 9
•8
log gram*
Figure 30.
Linearity of response to diazinon and parathion
with a platinum catalyst. Conditons: furnace
temperature, 725°, 02 reaction gas, 4 cc/min;
conductivity solvent, 10% isopropyl alcohol.
-------
72
n -
n -
e
o
Q.
—I"
•10
T
•9
1
•8
log grams
T
•7
T
•e
F:igure 31
Linearity of response to diazinon and parathion
with a platinum catalyst. Conditions: furnace
temperature, 725°; 0? reaction gas, 4 cc/min;
conductivity solvent, 75% isopropyl alcohol.
-------
73
f» -
e
e
a
a
e
94-
—r~
• 10
-j 1
•9 -8
log grams
T"
•7
1
•6
Figure 32.
Linearity of response to diazinon and parathion
with a platinum catalyst. Conditions: furnace
temperature, 800°; 02 reaction gas, 4 cc/min;
conductivity solvent, 10% isopropyl alcohol.
-------
74
H) -
I
e
e
e.
a>
o
Dlailnen
Pa rath ion
-10 -9 -8 -7 -6
log gram*
Figure 33. Linearity of response to diazinon and parathion
with a platinum catalyst. Conditions: furnace
temperature, 800°, 02 reaction gas, 4 cc/min;
conductivity solvent, 90% isopropyl alcohol.
-------
75
e
o
a
Dlazl non
Parathion
i
-10
•8
log grams
Figure 34. Linearity of response to diazinon and parathion
with a platinum catalyst. Conditions: furnace
temperature, 800°; Og reaction gas, 4oc/min;
conductivity solvent, 100% isopropyl alcohol.
-------
76
approximately 1 X 10 g/ml of water. Thus, even "100%" isopropyl alcohol
should contain sufficient water for the conversion of S0? and SO., to their
respective acids. The improvement in linearity at the upper concentration
range with water content of the conductivity solvent may therefore be a
function of solvent polarity, which is supported by the fairly good linearity
exhibited with methyl alcohol (See Figure 35).
Detector linearity at the upper concentration range is not significantly
influenced by the inside diameter of the reaction tube (Figure 29 and 36) or
the presence of quartz wool contact material (37). However, linearity at the
lower end of the concentration range is very sensitive to the condition of
the reaction tube and contact material. In some instances, poor response due
\
to a contaminated reaction tube can be improved by heating the tube overnight
at 950° with approximately 50 cc/min. of oxygen reaction gas.
Influence of Conductivity Cell Geometry on Detector Specificity to Sulfur-
Containing.Compounds. Coulsor? suggested that the selectivity to sulfur
compounds relative to hydrocarbons observed with the Coulson electrolytic
conductivity detector may be due to the very short gas-liquid contact time;
and since COp is slower to dissolve in water than SOp and SO.,, selectivity to
sulfur compounds should be observed. In an attempt to enhance detector specificity
to sulfur compounds, a conductivity cell that was designed to minimize gas-
liquid contact time and solvent surface area was compared to. the conventional
cell of the Model 310 Hall Electrolytic Conductivity Detector.
Details of design of the conventional cell and the alternate embodiment
are shown in Figures 38 and 39, respectively. In the conventional cell, the
conductivity solvent and the gaseous reaction products are combined in a small
Teflon tee (the gas-liquid contactor). Since the solvent has little affinity
for the Teflon surface and the i.d. of the tee is small, the gas and liquid
-------
77
m
c
o
a
9
O
Diailno n
Parathlon
8
log grams
i
6
Figure 35.
Linearity of response to diazinon and parathion with
a quartz wool contact material. Conditions: furnace
temperature, 850°; air reaction gas, 12 cc/min;
conductivity solvent, methyl alcohol.
-------
78
9
O
I
•10
I
-8
log gram*
Figure 3fi.
Linearity of response to diazinon and parathion.
Conditions: reaction tube, 1 mm. i.d. quartz;
furnace temperature, 900°; Q£ reaction gas, 4 cc/min;
conductivity solvent, 75% isopropyl alcohol.
-------
79
c
o
a A
a>
e
•10
I
•9
•8
log grams
Figure 37. Linearity of response to diazinon and parathion.
Conditions: furnace temperature; 625°; 02 reaction
gas, 4 cc/min; conductivity solvent, 25% isopropyl
alcohol.
-------
80
\
\
B
/
\
\
0.5 in.
Figure 38. Microelectrolytic conductivity detector cell assembly:
A, gas-liquid contactor; B, Teflon solvent delivery tube; C,
Teflon reaction products delivery tube; D, stainless steel
detector block; E, solvent vent (0.02 in); F, Teflon insulator
sleeve; G, gas-liquid exit tube and center electrode.
-------
81
\
n
B
c
-D
Figure 39. Alternate microelectrolytic conductivity
cell assembly: A, gas entrance tube; B, solvent
entrance; Cf stainless steel detector block; D, solvent
vent (0.02 in); E, Teflon insulator sleeve; F, gas-liquid
exit tube and center electrode.
-------
82
phases are well mixed. The heterogeneous gas-liquid mixture thus formed
separates into two smooth flowing gas and liquid phases upon contact
with the stainless steel surface of the outer electrode (Figure 38, D).
The liquid phase flows down the wall as a sheath with the gas phase as the core.
In so doing, the liquid phase passes between the inside wall of the detector
block (outer electrode) and the outside wall of the inner gas exit tube
(Figure 38, G). The solvent is finally vented via the solvent exit hole
(Figure 38, E) in the center electrode. In contrast, a heterogeneous gas-
liquid mixture is not formed in the conductivity cell design illustrated
in Figure 39. In this design, the solvent enters from the side of the cell
assembly (Figure 39, B) and proceeds around the Teflon gas entrance tube
(Figure 39;, A) and then flows down the inside wall of the outer electrode
(Figure 39;, C). From this point on the liquid and gas phases follow
the same paths as described for the other design. Since the gas and liquid
phases are not mixed, extraction of soluble gases occurs only at the gas-
liquid interface. The gas-liquid contact time and the solvent area exposed
to the gas phase can be altered by the distance that the Teflon gas entrance
tube is inserted into the cell.
The two cell designs were evaluated using a platinum catalyst and 25%
isopropyl alcohol. Detector responses to diazinon (5 ng), parathion (5 ng)
and a normal alkane mixture (2 yg each of C-|g, C-,g, C2Q, and Cp-i) were
determined using the conventional cell and the alternate embodiment with the
Teflon gas entrance tube inserted to various depths. Inserting the gas
entrance tube further into the cell decreased response to hydrocarbons.
However, it also decreased response to the sulfur compounds by the same
amount, arid no noticeable increase in selectivity was achieved by varying
the solvent surface area and the gas-liquid contact time. The two cell
designs exhibited essentially equivalent selectivities.
-------
83
An additional study was conducted to determine if the response to
hydrocarbons could be enhanced by greatly increasing the gas-liquid contact
time. In this study, the gas and liquid phases were mixed in a Teflon tee and
then passed through a 0.03-in. i.d. X 13-in. Teflon tube prior to the conduc-
tivity cell. Again, however, response exhibited no significant change.
It can be concluded from these studies that gas-liquid contact time does
not appreciably affect selectivity of the Hall Electrolytic Conductivity Detector.
Selectivity to sulfur compounds relative to hydrocarbons and esters must
therefore merely be a function of the relative quantities of SOp + SCL and CCL,
and their relative degree of ionization.
Evaluation of Nickel Tubing for the Detection of Sulfur-Containing
Compounds in the Catalytic Oxidative Mode. Considerable variability is
encountered in the detection of sulfur compounds with an empty quartz tube
or a quartz tube containing a contact material (or catalyst). This variability
is usually due to the condition of the reaction tube changing with time.
A reaction tube packed with a contact material or catalyst is particularly
susceptible to"poisoning" since the flow of gas may be restricted in certain
parts of the tube due to uneven packing. The area of the tube where the
flow stagnates is prone to carbonization and accumulation of other contaminants
from column and sample bleed.
A reaction tube that has an open and unrestricted path for gas flow,
moderate and constant surface reactivity and low adsorption of the reaction
products should improve detector performance. Nickel tubing has these
properties and was therefore evaluated for the detection of sulfur-containing
pesticides. Nickel tubing of the same length and internal dimensions as used
for the analysis of chlorine-containing compounds was used. Detector sensitivity
and specificity were determined using the same samples as employed in the quartz
reaction tube studies.
-------
84
The nickel reaction tubes require several days for equilibration. Peak
shape and sensitivity is usually poor until the tube has been conditioned
at furnace operating conditions for at least overnight. After conditioning,
however, sensitivity and peak shape are excellent. Chromatograms of a
variety of sulfur-containing pesticides are reproduced in Figures 40 and 41.
The need for conditioning is probably due to contamination of the
tubing during fabrication. It also probably takes a finite length of time
to form a steady-state layer of oxide and to deactivate any adsorptive sites.
Heating the outer end of the tube with a torch does not appear to help, and
usually increases tailing. Although not investigated in detail, furnace
temperature and reaction gas flow rate do not seem to affect conditioning
time. Preconditioning the tube by rinsing with acids or bases was not tried,
but the tube was rinsed with water and organic solvents to remove any soluble
contaminants.
The effects of furnace temperature and reaction gas flow rate on detector
response and selectivity to sulfur-containing compounds are presented in
Tables XXIII-XXVI. Detector response is reported relative to the peak height
at 600° which was assigned a value of 10. Selectivites were calculated from
peak heights and reported on a response per gram of sulfur relative to gram of
hydrocarbon or ester.
Detector response increases with furnace temperature from 600 to 750
and then decreases with higher temperatures (Table XXIII). However, selectivity
relative to hydrocarbons and esters is maximum at 650°. Selectivity decreases
rapidly with temperature, and is only approximately 150 at 950° (Table XXIV).
Though furnace temperature greatly affects detector response, the flow rate
of reaction gas does not. Response is maximum between 60 and 100 cc/min. of
air, but there is only about a 50% difference between the minimum and maximum
values (Table XXV). Flow rate also does not dramatically influence selectivity
relative to esters (Table XXVI). The effect of reaction gas flow rate on
-------
85
I Thimet
2 Malathion
3 Thiodan I
4 Thiodan II
5 Trithion
>
E
o>
(0
c
o
a
en
a>
oc
B
0 2 46 0246
Time (min.)
Figure 40. Representative chromatograms of sulfur pesticides
with a nickel reaction tube. Conditions: furnace
temperature, 850°; air reaction gas, 80 cc/min;
conductivity solvent, methyl alcohol; sample size,
A = 1 ng, B = 20 ng, attenuation, A = 1 X 0.4,
B = 10 X 0.2.
-------
86
>
E
o
4)
CC
B
o-
1 f
6 i
\
T ime (min.)
Figure 41. Representative chromatograms of diazinon and parathion
with nickel reaction tube. Conditions: furnace temp-
erature, 850°; air reaction gas, 80 cc/min; conductivity
solvent, methyl alcohol; sample size, A = 0.5 ng,
B = 5 ng; attenuation, A = 1 X 0.2, B = 1 X 0.4.
-------
87
Table XXIII. Influence of Furnace Temperature on Detector Response
to Sulfur-Containing Pesticides in the Catalytic
Oxidative Mode Using Nickel Tubing3'".
Compound0
Furnace Temperature ( C)
600 650 700 750 800 950 900 950
Diazinon 10 157 386 557 471 307 147 71
Parathion 10 150 500 725 625 600 300 200
aDetector response reported as relative peak heights with that at
600° assigned a value of 10.
Reaction gas flow rate was 80 cc/min air; conductivity solvent
was 25% isopropyl alcohol.
Sample quantity was 2 ng.
-------
88
Table XXIV. Influence of Furnace Temperature on Detector
Selectivity to Sulfur Compounds Relative to
Hydrocarbons and Esters in the Catalytic
Oxidative Mode Using Nickel Tubing .
Furnace Temperature
600
650
700
750
800
850
900
950
Selectivity
Hydrocarbons
> 11,670
>183,300
> 77,140
18,570
2,390
990
360
160
Esters
1,170
4,400
2,060
540
710
630
350
150
aReaction gas flow rate was 80 cc/min air; conductivity
solvent was 25% isopropyl alcohol
Selectivity relative to hydrocarbons was calculated
from peak heights for diazinon relative to H-Cio' and
relative to esters using ethyl dodecanoate. They are
based on the response per gram of element detected.
-------
89
Table XXV. Influence of Reaction Gas Flow Rate on Detector
Response to Sulfur-Containing Pesticides.a»b
Flow Rate (cc/min)
Compound
Diazinon
Parathion
30
10
10
60
16
16
80
12
11
100
14
12
150
9
6
200
9
7
aDetector response reported as relative peak heights with that at
30 cc/min. assigned a value of 10.
Furnace temperature was 650°; conductivity solvent was 25% isopropyl
alcohol.
cSample quantity was 2 ng.
-------
90
Table XXVI. Influence of Reaction Gas Flow Rate on Detector
Selectivity to Sulfur Compounds Relative to Esters
in the Catalytic Oxidative Mode Using Nickel
Tubing.3
Selectivity13
30
20,420
60
22,780
Flow
80
20,770
Rate (cc/min)
100
18,750
150
15,000
200
18,000
aFurnace temperature was 650°; conductivity solvent was 25% isopropyl alcohol.
Selectivity was calculated from peak heights of parathion and ethyl palmitate.
-------
91
selectivity relative to hydrocarbons was not investigated since no hydro-
carbon response was observed at 650°.
The influence of furnace temperature on detector selectivity was
investigated in greater detail using model compounds of such similar structure
that response could be attributed to a single element or functional group.
Thioanisole was used to determine sulfur response, rn-chlorotoluene for chlorine
response and methy p_-toluate for ester response.
The detector was operated with 100 % methyl alcohol as the conductivity
solvent and 80 cc/min. of air as the reaction gas. Methyl alcohol was used
as the conductivity solvent to suppress the nitrogen and ester response.
Selectivities were calculated on a response per gram of element or functional
group (-CO?R) basis using peak areas. The selectivities are reported in
Table XXVII.
Since both halogen^ and sulfur-containing compounds can be analyzed in
the oxidative mode, little selectivity for sulfur relative to chlorine
should be expected; and as shown in Table XXVII, there is indeed little
selectivity for sulfur. Selectivity to sulfur relative to halogens can be
improved by the use of a silver scrubber , if needed.
Selectivity to sulfur relative to nitrogen reaches a maximum of 252
at 825°, whereas selectivity to esters is at a maximum value of 10,308 at
875°. Although selectivity relative to esters and hydrocarbons (Table XXIV)
should be sufficient for most analyses, selectivity relative to nitrogen may
be insufficient. Therefore questionable samples should also be analyzed in
the reductive mode.
Minimum Detectable Quantity. The minimum detectable quantity of a sulfur-
containing compound depends upon its sulfur content and the operating conditions
-------
92
Table XXVII. Influence of Furnace Temperature on Sulfur .
Selectivity in the Catalytic Oxidative Mode. '
Furnace Temperature (°C)
750
775
800
825
850
875
900
925
950
Element
Cl
24
24
17
21
19
14
6
2
2
N
82
138
183
252
239
167
110
75
84
R-(Mj*0
1,988
3,011
4,100
6,524
8,967
10,308
6,293
4,042
4,444
aReaction gas flow rate was 80 cc/min of air; conductivity
solvent was 100% methyl alcohol.
Selectivities calculated from peak areas using thioanisole
(10 ng), m-tolunitrile (500 ng), tn-chlorotoluene (50 ng),
and methyl (0-toluate (10 yg).
-------
93
used.. In general, minimum detectable quantities are lower when a contact
material or catalyst is used. Minimum detectable quantities of 50-100 pg
can usually be obtained for diazinon and parathion. Minimum detectable
quantities for a variety of sulfur-containing pesticides are presented
in Tables XXVIII and XXIX. Representative chromatograms of low levels of
pesticides are reproduced in Figures 42 and 43.
-------
94
Table XXVIII. Minimum Detectable Quantities of
Diazinon and Parathion.
Compound
Conditions
10% Isopropyl alcohol
ARM-381
FT = 725°, 02 = 4 cc
Platinum catalyst
75% Isopropyl alcohol
AR.M-381
FT 725°, 02 = 4 cc
Platinum catalyst
100% Isopropyl alcohol
ARM-381
FT 800°, 02 = 4 cc
Platinum catalyst
25% Isopropyl alcohol
2/3 IRN-150 + 1/3 IRN-77
FT 650°, 02 = 4 cc
Quartz wool
100% Methyl alcohol
2/3 IRN-150 + 1/3 IRN-77
FT 700°, Air = 100 cc
Nickel tube
Diazinon
56 pg
(1.12)8
17 pg
(1.16)
8 P9
(1.12)
29 pg
(1.48)
40 pg
(1.12)
Parathion
91 pg
(2.04)
50 pg
(2.16)
13 og
(2.08)
100 pg
(2.88)
50 pg
(2.00)
aMinimum detectable quantities are that 2X noise and
short-term drift.
Values in parenthesis are retention times in minutes
-------
Table XXIX. Minimum Detectable Quantities of Sulfur-Containing Compounds.
Compound
Conditions
100% Methyl alcohol
1/2 IRN-150 + 1/2 IRN-77
FT = 850°, 02 =12 cc
Quartz wool
100% Methyl alcohol
1/2 IRN-150 + 1/2 IRN-77
FT = 850°, Air = 80 cc
Nickel tube
Methyl
Parathion
118 pg
(1.44)
Diallate
125 pg
(0.84)
68 pg
(0.84)
Thimet
9 pg
(0.72)
34 pq
(0.76)
Malathion Captan
15 pg 83 pg
(1.68) (2.41)
133 pg
(1.68)
Thiodan I
39 pg
(3.08)
200 pg
(3.04)
Thiodan II
100 pg
(4.16)
400 pg
(4.12)
Trithion
26 pg
(5.12)
182 pg
(5.32)
aMinimum detectable quantities are that 2X noise and short-term drift.
Values in parenthesis are retention time in minutes.
en
-------
96
>
£
Nickel Tube
Quartz Tube
a>
(A
G
o
a.
in
V
1.
2.
3.
4.
5.
6.
Thimet
Malathion
Captan
Thiodan I
Thiodan II
Trithion
Mgure 42.
4
8
Time (min.)
Chroma tograms of low levels of sulfur pesticides
with nickel and quartz reaction tubes. Conditions:
conductivity solvent, methyl alcohol; sample size;
nickel tube - 1 ng, quartz tube - 0.5 ng; attenuation,
nickel tube - 1 X 0.4, quartz tube - 1 X 1.6.
-------
>
E
co
c
o
0.
CO
B
UD
Time (min.)
Figure 43. Chromatograms of low levels of diazinon and parathion with
different conditions. Conditions (A): 0.1 ng, 25% isopropyl
alcohol, 625°, quartz wool contact material. Conditions (B):
0.5 ng, 50% isopropyl alcohol, 900°, empty quartz tube.
Conditions (C): 0.1 ng, 75% isopropyl alcohol, 725°; platinum
catalyst.
-------
98
Detection of Nitrogen-Containing Compounds
Optimization of Detector Operating Conditions. Nitrogen-containing
compounds are detected using the catalytic reductive mode. In this mode,
NH3, HX, HpS, HpO, CH. and lower alkanes are produced from organic compounds
containing nitrogen, halogen, sulfur and oxygen. Selectivity is acheived
by removing HX and hLS with a strontuim hydroxide abstractor. Water does
not give a response since it is already present in large excess in the
conductivity solvent. Methane and lower alkanes are not ionized and do
not give a response. Thus, selectivity is primarily a function of the
capacity and abstracting effeciency of the strontuim hydroxide scrubber.
"Conductivity Solvent and Reaction Systems-" Though the conversion of
organic nitrogen to NH~ is fairly straight forward, the measurement of trace
quantities of NHo by electrolytic conductivity is not. Ammonia must react
with water to form the ammonium and hydroxyl ions which are the charge
carriers.
NH3 + H20 ?=^ NH4+ +OH~
However, if the conductivity solvent is acidic, addition of ammonia will result
in the formation of an ammonium salt. Since the specific ionic conductance
HY + NH* OH" NH + Y~ +
of the ammonium ion is less than that of the proton and most negative ions
have a specific ionic conductance less than that of the hydroxyl ion, there
will be a decrease in electrolytic conductivity for trace quantities of
ammoni a .
Thus, the sensitive detection of nitrogen compounds without the formation
of negative peaks requires a slightly basic aqueous conductivity solvent
-------
99
that also has a low conductivity. The required basicity and low con-
ductivity can be maintained with an ion exchange resin tube packed with 2/3
Duolite ARA-366 (OH" form) on the bottom (pump side) and 1/3 IRN-150
on the top (cell side) similar to that previously described by Patchett .
Column bleed and impurities in the helium carrier gas may lower the
pH of the conductivity solvent and increase detector background. Attempts
to use helium as the carrier gas were only partially successful due to the
presence of impurities. Consequently, electrolytic hydrogen was used as the
carrier and reaction gas. The effect of column bleed, if minor, can be
compensated for by the addition of a very small amount (0.01 -0.1 cc/min)
of N~ to the reaction gas. Under the conditions of operation, a small per-
centage of the N2 is converted to NH3, which increases the pH of the con-
ductivity solvent and prevents the formation of negative peaks and loss of
sensitivity in the detection of low nanogram quantities of nitrogen compounds.
The addition of N~ to the reaction gas may cause a high and inconsistent
background that may take several days to subside. The background, after
equilibration»should be approximately 10 to 20% higher than that without Hy-
The conversion of N? to NH~ increases substantially from 825 to 875°. The
most uniform results are obtained at approximately 825 .
A variety of solvents and ion exchange resins were investigated for
the detection of nitrogen-containing compounds. The solvents included methyl
alcohol, acetonitrile, isopropyl alcohol with 0.1% methyl iodide, 1:1
isopropyl alcohol/water, 1:5 dimethylformamide/water, 1:2:20 dimethyl-
formamide/isopropyl alcohol/water, 1:10 acetonitrile/water, 1:10 isopropyl
alcohol/water and 1:7 isopropyl alcohol/water. The resins included Amberlite
IRN-150, Amberlite IRN-154, Amberlite IRN-78, Duolite ARM-381 and Duolite
ARA-366 (OH" form).
-------
100
The best performance was obtained with 10-15% isopropyl alcohol in
water and a resin tube packed as described above with IRN-150 and ARA"366.
The other conductivity solvents resulted in high background and/or poor
response. Response with pure water was as good as that obtained with 10%
isopropyl alcohol, but the baseline was noisy.
The influence of furnace temperature on detector response to CIPC,
atrazine and simazine is shown in Figure 44. Little response is observed
below approximately 750°. Response increases rapidly with temperature
up to 800 to 825° and continues to increase slightly from 825 to 850°.
Since the noise level in the presence of N« also increases wi
th
temperature and is excessive at 850°, the best performance is obtained
at approximately 825 . However, in the absence of N? (column bleed permitting)
a useful increase in sensitivity is obtained by operating at 850°.
Although response is temperature dependent, considerable changes
in the flow rate of the hydrogen reaction gas can be tolerated without
adverse effects. The influence of hydrogen reaction gas flow rate on
detector sensitivity to CIPC, atrazine and simazine is summarized in
Table XXX. It should be noted that the total hydrogen flow rate is
40 cc/min. greater, because 40 cc/min. of hydrogen carrier gas was used.
Under these conditions, the addition of 10 to 100 cc/min. of additional
hydrogen did not significantly affect detector response. Though there
is some variation of response with hydrogen flow rate, the data is in-
consistently variable. Repeating the experiment two additional times
resulted in the same trend.
The effect of solvent flow rate on detector response is shown in Figure
45. As would be expected, response is inversely proportional to solvent flow
-------
101
o
OH
___ o
$ o
e OH
e co
CL
»
«
K
CN
O
oH
850
Furnace T*mp. (°C)
Figure 44.
Influence of furnace temperature on response to
atrazine (A), simazine (•) and CIPC (•) .
-------
102
Table XXX. Influence of Hydrogen Reaction Gas Flow
Rate on Response to Nitrogen-Containing
Compounds9.
f*
Flow Rate (cc/min)
10
20
40
60
80
100
CIPC
27
32
37
32
38
31
Response
Atrazine
89
109
121
108
131
108
Simazine
78
95
109
95
116
96
Furnace temperature was 800 .
Response is peak heights in mm.
Total flow also contained 40 cc/min of H carrier.
-------
103
o
o-
E o
— w
* o
O1
o
o
Figure 45.
2 3 4
Solvent flow rat*
(ee/mln)
Influence of conductivity solvent flow rate on
detector response to atrazine.
-------
104
rate. The change in response is a little larger than the calculated
value. However, there is some evaporation of the solvent in the cell,
and a little larger response with a given decrease in flow rate would
therefore be expected.
Although the cell requires a flow rate 0.3 cc/min. to prevent peak
broadening, the short-term noise level was fairly independent of solvent
flow rate and was not significantly increased at low flow rates as has beerr reported
by Wilson and Cochrane . Detector baseline instability was observed
at flow rates of 2 to 4 cc/min., however. Optimum performance is therefore
obtained with flow rates of 0.3 to 0.6 cc/min.
Selectivity of response to nitrogen compounds is primarily dependent
upon the abstraction efficiency of the strontium hydroxide scrubber.
Selectivity to nitrogen relative to chlorine, sulfur and esters is
reported in Table XXXI. Selectivities in this table were calculated on
the basis of the response per gram of nitrogen relative to the response
per gram of an element or functional group using peak areas.
A mixture comprised of nv-chlorotoluene (1 yg), thioansiole (1 yg),
m-tolunitrile (10ng), and methyl £-tolunate (1 yg) was used to determine
selectivities. The quartz reaction tube contained a nickel catalyst made
of a sufficient number of strands of 0.01~in. x 1.5 in. nickel wire so
that it fit securely in the tube. The catalyst bed was positioned in the
center of the hot zone. A strontium hydroxide scrubber (10% on glass wool)
approximately 0.5 in. long was positioned in the tube just inside the
end plate of the furnace.
-------
105
Table XXXI. Selectivity to Nitrogen
Relative to Halogen, Sulfur
and the Ester Function3>b.
Group Selectivity
Cl >12,870
0 S 330
-C-O-R > 1,700
Conditions: Furnace, 800 ; H2 flow
rate, 100 cc/min; solvent, 15%
isopropyl alcohol at 0.4 cc/min.
Selectivities calculated from peak areas,
-------
106
No response was observed for m-chlorotoluene or methyl £-toluate,
which results in selectivities for nitrogen relative to chlorine and the
ester function of >12,870 and >1,700, respectively. A significant response
was observed for 1 pg of thioanisole, and selectivity to nitrogen relative
to sulfur is only 330. Selectivity to nitrogen relative to hydrocarbons,
r /•
estimated from the response to the hexane solvent, is approximately 10 to 10 .
"Reduction of Peak Tailing and Baseline Noise." Peak tailing in
the nitrogen mode is usually due to insufficient basicity of the conductivity
solvent or a badly contaminated scrubber. Peak tailing due to insufficient
basicity is readily recognized by a sharp dip in the baseline just prior
to the peak followed by a negative dip after the peak that gradually
increases to the baseline (see Figure 46). The peak may be totally negative
if the solvent is acidic or the quantity of nitrogen compound is small.
Peak tailing due to contamination merely exhibits a trailing positive response.
A contaminated catalyst can also result in peak tailing similar to that exhibited
by a contaminated scrubber. Baseline noise is usually a result of the
conductivity solvent or a leak in the system.
Peak tailing and baseline noise are usually eliminated by using 15%
isopropyl alcohol as the conductivity solvent, an ion exchange tube packed
with Amberlite IRN-150 and Duolite ARA-366 (OH" form), the addition of a small
quantity of N~ to the reaction gas (if required) and routine maintenance of
the catalyst, solvent, ion exchange tube and scrubber. If the solvent
is vented, the catalyst usually lasts for at least three to four months.
The conductivity solvent should be replaced approximately every two weeks.
The ion exchange resin normally lasts for approximately three to five
months. The scrubber should be replaced as needed.
-------
B
Figure 46. Peak shapes obtained for nitrogen-containing compounds: A, normal
peak; B, peak obtained with an insufficiently basic conductivity
solvent; C, peak obtained with an acidic conductivity solvent.
-------
108
Linearity of Response to Nitrogen-Containing Compounds. Linearity of
response at the lower end of the sensitivity range (0.1-10 ng) is
dependent upon the basicity of the conductivity solvent. At a pH slightly
above 7.0 response is very linear. However, if the conductivity solvent
is acidic, linearity is very poor for lower sample quantities. Under
normal operating conditions the detector displays a fairly linear response over
approximately three to four orders of magnitude (0.1 ng - 1 yg). Response
tends to level-off slightly at the upper concentration range, which may
be due to swamping the catalyst or the solution chemistry of ammonia.
Detector linearity from 0.5 ng to 1 yg is shown in Figure 47 for
CIPC and atrazine. Linearity from 1 ng to 1 yg is shown in Figure 48
for trifluralin, IPC and PCNB. Detector response at the nanogram level
is plotted for CIPC, atrazine and simazine in Figure 49. These Figures show
the excellent linearity that is displayed by the electrolytic conductivity
detector for a variety of nitrogen-containing compounds.
Minimum Detectable Quantity. The minimum detectable quantity of
nitrogen is primarily dependent upon polarity and correct basicity of the
conductivity solvent. Optimum conditions for minimum detectability are
the same as those for maximum linearity (15% isopropyl alcohol as the conductivity
solvent and stacked IRN-150 and ARA-366 ion exchange resins). Minimum
detectable quantities of 40 to 50 pg for atrazine and simazine at retention
times of approximately 3 minutes can be routinely obtained. Minimum detectable
quantities of a variety of nitrogen-containing pesticides are reported
in Table XXXII. Chromatograms of low levels of nitrogen-containing
pesticides are shown in Figures 50 and 51.
-------
109
n> -
e
o
a
Atr az i ne
C I P C
•9 -8 -7
log grams
Figure 47. Linearity of response to atrazine and CIPC.
-------
no
c
e
a
o
I
•a
i
•e
log grams
Figure 48. Linearity of response to trifluralin (•) ,
IPC (A) and PCNB (•).
-------
Ill
O
8-
o
o-
00
o
o-
•o
E
E
e
e
a
« S-
o
o-
o
o-
I
2
4 6
Concentration (ng)
i
8
r
10
Frigure 49.
Linearity of response to CIPC (•) , atrazine (4),
and simazine (•) from 1 to 10 ng.
-------
112
Table XXXII. Minimum Detectable Quantities of Various Nitrogen-.
Containing Compounds9.
Compound
Conditions
10% Isopropyl alcohol
1/3 IRN-150 + 2/3 IRN-78
FT = 800°, H2 = 80 cc
Quartz tube with
nickel catalyst
Trifluralin CIPC
llOpg 140pg
(0.96P (1.52)
IPC
190pg
(1.60)
PCNB
400pg
(2.00)
Atrazine
37pq
(2.16)
Simazine
33pg
(2.88)
aMinimum detectable quantities are 2x noise and short-term drift.
Values in parenthesis are retention times in minutes.
-------
>
E
o>
0)
CO
0)
so pg
10x0.1
2 3
100 pg
(0 x o.i
500 P9
10 X 0.4
I
JL
4
Time
2
(mi n.)
2
Figure 50. Chromatograms of low levels of CIPC (1), atrazine (2) and simazine (3).
-------
0)
0)
c
o
a.
ID
0>
oc
0.5 ng 1.0 ng 5.0 ng
10X0.1 10X0.2 10X0.8
AiJL A,
i
Jl)L_ J^
624 6
2 4 ^
<
\l
i 2 4
Time (m i n.)
Figure 51. Chromatograms of low levels of trifluralin (1), IPC (2)
and PCNB (3).
-------
115
APPLICATIONS
Detector utility for the determination of trace quantittes of halogen-,
sulfur- and nitrogen-containing compounds was evaluated for a wide variety
of compounds and sample types. The primary objectives of this study were
to determine the degree of interference from co-extracted naturally occuring
and laboratory introduced contaminants and to ascertain the influence of
these contaminants on detector response in the different modes of operation.
Attempts were made to conduct this evaluation under similar analytical situations
Thus when possible, the same extraction procedure and chromatographic con-
ditions were used so that interference in the various modes of operation
could be directly compared. Consequently, the procedures used do not
necessarily represent the best procedure for a given compound, but do
represent general procedures that provide adequate performance. Also,
attempts were not made to optimize recoveries since that was not the objective
of this study.
This evaluation was complicated by the general lack of information re-
garding extraction and cleanup procedures for many of the compounds studied.
The large number of operation parameters studied and the need to investigate
numerous cleanup procedures for soil and biological extracts often required
amendments in analytical methodology to be made in "mid-stream" in order
for the study to be completed in the short time available. For instance,
paraffin oil was used as a "keeper" for the analysis of sulfur compounds
in the pyrolytic mode, but mineral oil was found to slowly "poison" the
nickel catalyst in the determation of nitrogen compounds in the catalytic
reductive mode and was thus deleted for nitrogen compounds.
-------
116
Analysis of Chlorine-Containing Pesticides in the Presence of PCB and
PCN in Water SoTl and Biological Samples.
Chlorinated hydrocarbon pesticides were analyzed in the presence of
PCB and PCN with the detector operated in the catalytic oxidative mode for
water and fat samples, and in the pyrolytic mode for soil samples. A 0.02 in.
i.d. nickel reaction tube and methyl alcohol conductivity solvent were
used for the catalytic oxidative mode; and a 2 mm i.d. quartz reaction tube
and ethyl alcohol were used for the pyrolytic mode. Furnace temperatures
and reaction gas flow rates are described under specific analyses.
Analysis of Chlorine-Containing Pesticides in Water. Water samples
(500 ml) were fortified by the addition of 1.0 ml of an ethanolic solution
of pesticides (lindane, heptachlor, aldrin, heptachlor epoxide and dieldrin),
PCB (Aroclor 1254) and PCN (Halowax 1013). The PCB and PCN concentrations
were always lOx that of the individual pesticides. The water samples were
extracted 3x with 10 ml of 1:3 ether/hexane and the extracts combined. The
combined extracts were dried with approximately 1 g of Na^SC,, and then
reduced in volume to near dryness. The reduced extract was quantitatively
transferred to a 15-ml culture tube with approximately 5 ml of hexane. The
transferred extract was evaporated at room temperature with a gentle stream
of dry air. A Florisil trap was used to remove any impurities from the
air stream. The extracts were dissolved in hexane (1.0 or 10.0 ml) for gas
chromatographic analysis.
The extracts were analyzed with a furnace temperature of 800 and 100
cc/rnin of air reaction gas. Recoveries of the pesticides at 100 ppt,
400 ppt, I ppb and 10 ppb are summarized in Table XXXIII. Representative
chromatograms of the extracts are shown in Figure 52. Recoveries ranged from a low
of 62% for heptachlor at 100 ppt to a high of 110% for heptachlor epoxide at 100 ppt
-------
117
Table XXXIII. Recovery of Chlorinated Hydrocarbon Pesticides
from Water in the Presence of PCB and PCNa.
% Recovery
Pesticides
Lindane
Heptachlor
Al dri n
Hept. epox.
Die! dri n
100 ppt
70
62
83
no
98
400 ppt
84
81
73
107
90
1 ppb
73
72
82
91
99
10 ppb
71
71
73
86
87
Water samples contained PCB and PCN in a 10-fold excess,
DRecoveries are the average of three replicates.
-------
B
>
E
0)
V)
c
o
a.
m
a>
cc
CO
024 024 02
Time (min.)
Figure 52. Chromatograms of chlorinated pesticides extracted from
water. Sample: A, control, attenuation = 1 X 0.4;
B, 100 ppt, attenuation =1 X 0.4; C, 1 ppb, attenuation =1 X 1.6.
-------
119
Heptachlor epoxide and dieldrin consistently gave the highest recoveries, whereas
lindane and heptachlor usually gave the lowest recoveries. Since lindane and
heptachlor are the most volatile and gave the lowest recovery, there may
have been some loss of these pesticides due to their volatility.
The riean recovery for the five pesticides at the four concentration
levels was 83% with a standard deviation of 13.1. This recovery is good
when it is; considered that the analyses were conducted in the presence of
a large excess of PCB and PCN. The average recovery and standard deviation
could probably be improved by using more elaborate techniques of solvent
evaporation.
Analysis of pesticides in samples that contain PCB and PCN by classical
techniques, using electron capture detection requires the physical isolation
of the pesticides by column chromatography. In our hands, this was found to
require initial separation on a Florisil column followed by further isolation
on coconut: charcoal and silica gel columns. Overall recoveries by these
techniques were found to be quite low and varied considerably. Also,
separation of some pesticides from PCB and PCN by multiple column
chromatography is not complete. Thus, the analysis of pesticide-PCB-PCN
mixtures by selective detection is considerably easier and usually gives as
good or better results.
Analysis of Chlorine-Containing Pesticides in Soil. Soil samples (25 g)
were fortified with 1.0 ml of a hexane solution of pesticides (lindane, heptachlor,
aldrin, heptachlor epoxide and dieldrin), PCB (Aroclor 1254) and PCN (Halowax
1013). The PCB and PCN concentrations were lOx the level of the individual
pesticides. The soil samples contained in 250 ml erlenmeyer flasks, were
wetted with 5 ml of water and extracted by shaking with 100 ml of 1:1
-------
120
hexane/isopropyl alcohol on a wrist-action shaker for 15 m1n. The extract
was filtered through Whatman 2-V fluted filter paper. The flask was rinsed
with an additional 10 ml of solvent, which was also used to .wash the filter
paper. The filtrate was then reduced to near dryness on a rotary evaporator.
The reduced extract was quantitatively transferred to a culture tube (15 ml)
with approximately 5 ml of hexane. The extract was evaporated with a gentle
stream of air, and the remaining residue dissolved in hexane (1.0 or 10 ml)
for gas chromatographic analysis.
The extracts were analyzed using a furnace temperature of 700 and a
hydrogen reaction gas flow rate of 2 cc/min. Recoveries of the pesticides
at 0.01 ppm, 0.1 ppm, 1.0 ppm and 10.0 ppm are presented in Table XXXIV.
Representative chromatograms of the soil extracts are reproduced in Figures
53-55. Recoveries at 0.1, 1.0 and 10.0 ppm were good and ranged from 74
to 98% with a mean (for all the pesticides) of 85% and a standard deviation
of 6.5. Recoveries of the more volatile pesticides tended to be a little
lower than the less volatile ones. However, this difference was lower
than in the water analysis. The extracts contained some residue from the soil
which could have minimized loss due to volatilization.
Although the recoveries at 0.1, 1.0 and 10.0 ppm were good and the
pesticides could easily be analyzed in the presence of an excess of PCB and
PCN 10x that of the individual pesticides, recoveries at the 0.01 ppm level
were low, with the exception of dieldrin. The extracts contained a number
of small peaks at the retention times of the first four pesticides. The
intensity of these peaks was variable and thus the substraction of their
i
response from that of the pesticides resulted in variable and low recoveries
for these compounds. These impurities were not removed by a Florisil cleanup
column. Thus, the lower level of analysis for these particular samples is
estimated to be approximately 0.03 ppm.
-------
121
Table XXXIV. Recovery of Chlorinated Hydrocarbon Pesticides
from Soil in the Presence of PCB and PCNa.
% Recovery
Pesticide
Lindane
Heptachlor
Aldrin
Hept. epox.
Dieldrin
0.01 ppm
37
42
53
65
85
0.1 ppm
85
84
98
90
96
1 .0 ppm
78
74
79
84
85
10.0 ppm
79
86
81
87
85
Samples contained PCB and PCN in a 10-fold excess,
^Recoveries are the average of three replicates.
'Sample contained 50 g of soil.
-------
122
>
E
B
at
c
o
a
v>
a
oc
o
Time
(min.)
Figure 53.
Chromatograms of chlorinated pesticides extracted
from soil. Sample: A, 2.5 ng of pesticides,
attenuation = 1 X 1.6; B, 0.01 ppm, attenuation = 1 X
1.6.
-------
123
>
E
B
0
cc
L
JU
r
Ti me
(min.)
Figure 54. Chromatograms of chlorinated pesticides extracted
from soil. Sample: A, control, attenuation = 10 X 0.2;
B, 0.1 ppm, attenuation = 10 X 0.2.
-------
124
>
E
9)
in
c
o
a
CO
4)
CC
6
4
Time ( m i n.)
Figure 55. Chromatogram of soil extract fortified with 1 ppm
of chlorinated pesticides. Attenuation: 10 X 3.2.
-------
125
Analysis of Chlorine-Containing Pesticides in Fat Samples. The analysis
of chlorinated hydrocarbon pesticides in fat was attempted with fish fat,
lard, and chicken fat. Hexane extracts of fat (10 g) were fortified with
pesticides (lindane, heptachlor, aldrin, heptachlor epoxide and dieldrin),
PCB (Aroclor 1254) and PCN (Halowax 1013). The PCB and PCN concentrations
were lOx that of the pesticides. Separation of the pesticides from the lipids
was attempted by liquid-liquid partitioning followed by a Florisil cleanup as des-
cribed in Section 5,A,(1) of the EPA "Manual of Analytical Methods", Research
Triangle Park, NC. Separation of the pesticides from the lipids was also
attempted by liquid-liquid partitioning with hexane and 95%methyl alcohol.
In all cases, a considerable amount of fat (approximately 0.25-1 g) remained
in the final extract. The acetonitrile/hexane Florisil column procedure was
also used for 1-g fat samples.
The extracts were dissolved in hexane (1.0 to 10.0 ml) and analyzed
using a furnace temperatures of 700 to 750° and hydrogen reaction gas
flow rates of 0 to 5 cc/min. However, analysis was unsuccessful. After
approximately five to six injections, detector sensitivity and peak shape
deteriorated to such an extent that quantisation was impossible (see Figure 56).
Analysis was also attempted with a nickel reaction tube operated in the
catalytic oxidative mode at a furnace temperature of 780° (selective to
aliphatic chlorine). The same results were obtained, however.
"D
Sensitivity and peak shape were partially restored by changing the
reaction tube, but they were not fully restored until the column and
transfer lines were cleaned. The inlet side of the column had a dark brown
residue (after approximately 30 injections), which required replacing the
first 6 in. of column packing. It can thus be concluded, that the analysis
-------
126
>
E
d>
CO
c
o
Q.
0)
0
DC
B
0
1 4
Time {mi n.)
Figure 56. Chromatograms of the chlorinated pesticide mixture
before and after the injection of fat extracts, t
Sample: A, 2.5 ng of chlorinated pesticides prior
to injection of fat extracts; B, 2.5 ng of chlorinated
pesticides after the injection of approximately
20 extracts.
-------
127
of lipid extracts is not feasible until more effective cleanup techniques
are developed. Although the cleanup procedures employed may be sufficient
for the analysis of dilute sample extracts by electron capture detection,
they are not adequate for the determination of the fairly concentrated
lipid samples required with the electrolytic conductivity detector.
Analysis of Sulfur-Containing Pesticides in Mater, Soil and Biological
Samples.
Sulfur-containing pesticides in water and alfalfa were analyzed with
the detector operated in the catalytic oxidative mode. A 0.02-in. i.d.
nickel reaction tube, 100 cc/min. of air reaction gas, and methyl alcohol
conductivity solvent were used. Sulfur-containing pesticides in soil were
analyzed in the pyrolytic mode with a 1-rrni i.d. quartz reaction tube packed
with approximately 0.25 in. of quartz wool. Air at a flow rate of 20 cc/min.
was used as the reaction gas and methyl alcohol as the conductivity solvent
in the pyrolytic mode.
Analysis of Sulfur-Containing Pesticides in Water. Water samples (500 ml)
were fortified by the addition of 1.0 ml of an ethanolic pesticide mixture.
Three different pesticide mixtures were used. One mixture contained Thimet,
malathion, captan, Thiodan I, Thiodan II and trithion. A second solution
contained diazinon, methyl parathion and parathion. The third solution con-
tained dial late. The water samples were extracted as described for the
analysis of chlorine containing pesticides in water.
The extracts were analyzed with the detector operated at 650°. Recoveries
of the pesticides at 100 ppt, 400 ppt, 1 ppb and 10 ppb are reported in
Table XXV. Representative chromatograms of water extracts are exhibited
-------
128
Table XXXV. Recovery of Sulfur-Containing Pesticides for Water.
% Recovery3
Pesticides
Dial! ate
Diazinon
Methyl Para th ion
Parathion
Thimet
Malathion
Captan
Thiodan I
Thiodan II
Trithion
100 ppt
78
96
110
96
67
76
65
77
93
77
400 ppt
88
83
96
113
69
72
79
83
77
80
1 ppb
73
70
98
80
70
86
99
117
102
91
10 ppb
81
87
91
90
79
87
91
79
75
89
Recoveries are the average of three replicates.
-------
129
in Figures 57-59. The ten pesticides were recovered at the four con-
centration levels with an overall mean of 85% and a standard deviation of
12.4. The lowest recoveries were obtained for Thimet and captan, which can
possibly be attributed to the volatility of Thimet and the poor chromatography
of low quantities of captan. Recoveries, however, showed as much variability
between concentration as they did between pesticides. This indicates
that minor variations in technique such as evaporation time, evaporation
temperature, and surface activity of the evaporation vessel may be more
important than the individual pesticides analyzed. Nevertheless * as shown
in Figures 58 and 59, the electrolytic conductivity detector can be
used for the analysis of low concentrations of sulfur-containing pesticides
in water.
During the course of this study, it was noticed that deionizad water
contained a moderately high level of numerous sulfur-containing compounds
that exhibited detector responses equivalent to approximately 300 to 600 ppt
of the sulfur pesticides. The removal of these impurities required careful
distillation. Impurities in Na^SO. also presented a problem, and required
that the Na2S04 be soxhlet extracted and heat treated at 180° for 24 hr.
Consequently, due care should be exercised in the analysis of trace quantities
of pesticides in water.
Analysis of Sulfur-Containing Pesticides in'Soil. Soil samples (25 g)
were fortified with hexane solutions of the same three mixtures of pesticides
as described for water analysis. The soil was fortified at levels of 0.01,
0.1, 1.0 and 10.0 ppm. The soil was extracted as described for the analysis
of chlorinated hydrocarbon pesticides in soil, except 1 ml of 10% paraffin
oil in hexane was added to the filtrate as a "keeper".
-------
!••__
1
0)
c
o
Q.
M
0
oc
-
' IJ
6
A B C
^~~'
'U
^-Jv__
1
•
L
i
v
* 4 6*4 6*4
Time (min.)
Figure 57. Chromatograms of diazinon (1) and parathion (2) extracted
CO
o
from water. Sample: A, control, attenuation = 1 X 0.2;
B, 100 ppt, attenuation = 1 X 0.2; C, 1 ppb, attenuation = 10 X 0.2.
-------
o>
w
c
o
0.
(0
0
oc
B
\J
4 «
i i
A
4 i 4 i
Time (mi n.)
Figure 58. Chromatograms of Thimet (1), malathion (2), captan (3),
Thiodan I (4), Thiodan II (5) and trithion (6) extracted
from water. Sample: A, control, attenuation = 1 X 0.4;
B, 100 ppt, attenuation = 1 X 0.4; C, 1 ppm, attenuation = 10 X 0.1
-------
132
in
>
E
0)
(A
C
o
a
(A
a>
cc
B
0
Figure 59.
T
2
0
2
Time (m in.)
Chromatograms of dial late (1) and methyl parathion (2)
extracted from water. Sample: A, control, attenuation
1 X 0.4, B, 400 ppt, attenuation = 1 X 0.4.
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133
Recoveries are displayed in Table XXXVI, and representative chromatograms
of the analyses are shown in Figures 60-62. As shown by the data in this table,
diazinon, methyl parathion, parathion and captan could not be determined at
the 0.01 ppm level. The presence of contaminants and/or insufficient response
precluded those particular analyses. The other pesticides were determined
with excellent recoveries. The mean recovery for all analyses was 93% with
a standard deviation of 10.3.
Attempts to remove sample interference with a Florisil cleanup column
resulted in low and variable recoveries. Recoveries were not significantly
improved by different elution solvents or different Florisil activities.
Florisil activities that gave good recoveries failed to remove the sample
impurities,. A cleanup procedure was therefore not used. The sample extracts
were distinctly yellow, and the reaction tube had to be cleaned and the quartz
wool contact material replaced weekly.
Analysis of Sulfur-Containing Pesticides in Alfalfa. Alfalfa samples
(10 g) were fortified with a hexane solution of Thimet, malathion, Thiodan I,
Thiodan II and trithion. Samples were fortified at 0.02, 0.1, 1.0 and 10.0 ppm.
Samples were extracted by blending with acetonitrile (40 ml) for 2 mi a with
a Sorvall omnimixer. The blender cup was rinsed with acetonitrile and the
extract filtered. The filtrate was evaporated on a rotary evaporator until
only a small aqueous residue was left. The residue was transferred to a
separatory funnel with ether, approximately 5 ml of 10% aqueous NaCl added
and extracted three times with 15 ml of ether. The ether was then evaporated,
the residue dissolved in 2 ml of ether and quantitatively transferred to a
4:1 Flortsil/Celite cleanup column that contained 10% water. The shell
column was packed with 5 g of Florisil-Celite and contained 1 in. of Na$0
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134
Table XXXVI. Recovery of Sulfur-Containing Pesticides from Soil.
% Recovery9
Pesticide
\
Dial late
Diazinon
Methyl Parathion
Parathion
Thimet
Malathion
Captan
Thiodan I
Thiodan II
Trithion
0.01 ppm
88
--
—
--
78
92
—
93
94
91
0.1 ppm
100
93
103
100
95
101
95
62
63
99
1.0 ppm
95
101
105
101
100
105
71
97
98
100
10.0 ppm
101
91
88
92
89
95
89
100
101
90
Recoveries are the average of three replicates.
-------
>
E
o>
c
o
Q.
(0
e
oc
B
co
01
o i 4
Time
(min.)
Figure 60.
Chromatograms of jhimet (1), malathion (2), captan (3),
Thiodan I (4), Thiodan II (5) and trithion (6) extracted
from soil. Sample: A, control, attenuation = 1 X 1.6;
B, 0.01 ppm, attenuation = 1 X 1.6, C, 1 ppm,
attenuation = 10 X 3.2.
-------
9-
>
E
0
(0
c
o
a.
(0
o
oc
o-
B
co
12
VJ
Figure 61.
Chromatograms
parathion (3)
attenuation =
Time (mi n.)
of diazinon (1), methyl parathion (2) and
extracted from soil. Sample: A, control,
1 X 1.6; B, 0.1 ppm, attenuation = 1 X 1.6;
C, 1 ppm, attenuation = 1 X 3.2.
-------
>
E
o>
w
c
o
a.
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138
on the top and bottom. The column was washed with 10 ml of hexane prior
to the addition of the extract, which was added to the column in 20 ml of
10% ether in hexane. The column was eluted with 100 ml of 10% ether in
hexane. The eluate was evaporated to near dryness on a rotary evaporator,
quantitatively transferred to a culture tube and evaporated to dryness with
a dry, filtered stream of air. The residue was dissolved in hexane (1.0 to
10.0 ml) for chromatographic analysis.
Although the cleanup column effectively removed the chlorophylls and
water soluble components, it did not remove the carotenoids and other
oil soluble components. The purified extracts were dark yellow and exhibited
a number of gas chromatographic responses that prevented analyses at the 0.01
ppm level. Liquid-liquid partitioning between acetonitrile and hexane reduced
the intensity of the yellow color, but did not remove the interference.
The interfering peaks also displayed the same response-furnace temperature
relationship as the pesticides.
The extracts were analyzed in the catalytic oxidative mode at a
furnace temperature of 860°. Recoveries of the pesticides are tabulated in
Table XXXVII, and representative chromatograms of the extracts are shown
in Figure 63. The pesticides were recovered with an overall mean of 85%
and a standard deviation of 7.9.
The Florisil-Celite column was the only cleanup column investigated that
provided adequate sample cleanup without pesticide loss. Other columns
investigated included Flon'sil, alumina and silica gel of various activities.
The alfalfa constituents that were not removed by the cleanup column did
not appear to deteriorate sensitivity or peak shape.
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139
Table XXXVII. Recovery of Sulfur-Containing Pesticides
from Alfalfa.
% Recovery9
Pesticide
Thimet
Malathion
Thiodan I
Thiodan II
Trithion
\
0.02 ppm
87
73
83
93
87
0.1 ppm
87
95
86
65
95
1 .0 ppm
75
83
87
86
88
10.0 ppm
72
83
91
89
88
Recoveries are the average of three replicates,
-------
>
E
B
c
o
a
(0
o
cc
-p.
o
r
T
"T
T
T
T
T
Time {mi n.)
Figure 63.
Chromatograms of Thimet (1), malathion (2), Thiodan I (3),
Thiodan II (4), and trithion (5) extracted from alfalfa.
Sample: A, control, attenuation = 1 X 0.8; B, 0.02 ppm,
attenuation = 1 X 0.8; C, 1 ppm, attenuation = 10 X 0.2.
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141
Analysis of Nitrogen-Containing Pesticides in Water, Soil and Biological
Samples.
Nitrogen-containing pesticides were analyzed in the catalytic reductive
mode with a quartz reaction tube, nickel wire catalyst, 15% isopropyl alcohol
conductivity solvent and a furnace temperature of 820°. A strontium hydroxide
scrubber v/as placed in the quartz tube just within the furnace wall.
Analysis of Nitrogen-Containing Pesticides in Water. Water samples
(1 1) were fortified at 100 ppt, 400 ppt, 1.0 ppb and 10 ppb by the addition
of 1.0 ml of a pesticide solution. Two mixtures of pesticides were used. One
of the solutions contained CIPC, atrazine and simazine dissolved in methyl
alcohol, and the other contained trifluralin, IPC and PCNB dissolved in 4%
ethyl alcohol in hexane. The water samples were fortified at 100 ppt,
400 ppt, 1.0 ppb and 10.0 ppb. Two grams of NaCl were added to each sample.
The samples were extracted 3x with 50 ml of methylene chloride. The extracts
were combined, dried with Na2S04 and evaporated to near dryness on a rotary
evaporator. The reduced extract was then quantitatively transferred to a
15-ml culture tube that contained 1 ml of a 1% solution of pentadecane in
hexane. The extract was evaporated with a gentle stream of dry air (filtered
with Florisil) and the residue dissolved in hexane (1.0 or 10.0 ml).
Recoveries of nitrogen-containing pesticides from water are shown
in Table XXXVIII. In general, recoveries increased with concentration for
all compounds. The relatively low recoveries obtained at the 100 ppt level
were due to pesticide loss during evaporation of the solvent. When compared
to controls that were treated in the same manner as the water samples
(except no water was envolved), recoveries were essentially 100% for all
compounds. The effect of greater concentrations of pentadecane or more
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142
Table XXXVIII. Recovery of Nitrogen-Containing Pesticides
from Water.
% Recovery3
Pesticide
CIPC
Atrazine
Simazine
Trif luralin
IPC
PCNB
100 ppt
70
68
64
49
46
45
400 ppt
—
91
85
60
51
55
1 ppb
83
85
85
66
58
67
10 ppb
87
97
90
77
72
68
Recoveries are the average of three replicates.
-------
143
efficient "keepers" was not studied, but probably would result in improved
recoveries;. Representative chromatograms of the water extracts are reproduced
in Figures; 64 and 65.
Analysis of Nitrogen-Containing Pesticides in Soil. Soil samples (25 g)
were fortified at 0.02 (0.01 for atrazine and simazine), 0.1, 1.0 and 10.0 ppm
by the addition of 1.0 ml of methanolic solutions of the same two pesticide
mixtures as used in the water analysis. The samples were extracted as
described for the analysis of halogen- and sulfur-containing pesticides
in soil. The concentrated extract was cleaned up on a as-received Florisil
column. The Florisil column contained approximately 1 in. of Na2$0. on the
top and 5 g of Florisil. The extract was transferred to the column with
approximately 2 ml of benzene, and the pesticides eluted with an additional
20 ml of benzene. The benzene was evaporated and the residue dissolved in
hexane (1.0 or 10.0 ml) for gas chromatographic analysis.
Recoveries of nitrogen-containing pesticides from soil are summarized
in Table XXXIX. Recoveries ranged from 51% for IPC at 0.02 ppm to 93%
for trifluralin at 1.0 ppm. Recoveries for IPC and PCNB were relatively
low for 0.02 and 0.1 ppm. The low recovery was due in part to pesticide
loss on the cleanup column. Approximately 25 to 30% of IPC and 10 to 20%
of PCNB were lost on the cleanup column (compare the 1.0 and 10.0 ppm levels
with the 0.02 and 0.1 ppm levels). The other nitrogen-containing pesticides
were recovered from the cleanup column with little loss. Representative
chromatograms of the soil extracts are shown in Figures 6€ and 67.
Analysis of Nitrogen-Containing Pesticides in Alfalfa. Alfalfa samples
(10 g) were fortified with two pesticide mixtures. CIPC, atrazine and
simazine constituted one mixture, and trifluralin, IPC and PCNB constituted
-------
>
E
B
c
o
a
(0
a
cc
Time (m i n.)
Figure 64. Chromatograms of CIPC (1), atrazine (2) and simazine (3)
extracted from water. Sample: A, control, attenuation =
10 X 0.2; B, 100 ppt, attenuation = 10 X 0.2; C, 1 ppb,
attenuation = 10 X 0.4.
-------
>
E
B
o>
-------
146
Table XXXIX. Recovery of Nitrogen-Containing Pesticides
from Soil.
% Recovery3
Pesticide
CIPC
Atrazine
Simazine
Trifluralin
IPC
PCNB
0.02 ppm
--
83b
76b
68
51
60
0.1 ppm
75
77
69
81
51
65
1 .0 ppm
63
75
70
93C
81C
80C
10.0 ppm
69C
75C
79C
85C
75C
70C
aRecoveries are the average of three replicates.
Recovery is for 0.01 ppm.
p
No cleanup procedure was used.
-------
>
E
CO
c
o
a
a>
o
cc
Figure 66.
i 4
Time (m i n.)
Chromatograms of CIPC (1), atrazine (2) and simazine (3)
extracted from soil. Sample: A, control, attenuation =
10 X 0.2; B, 0.01 ppm, attenuation = 10 X 0.2; C, 1 ppm,
attenuation = 10 X 0.8.
2
-------
>
E
B
o>
c
o
a.
(A
0
E
00
Figure 67. Chromatograms of trifluralin (1), IPC (2) and PCNB (3)
extracted from soil. Sample: A, control, attenuation =
10 X 0.4; B, 0.02 ppm, attenuation = 10 X 0.4; C, 1 ppm,
attenuation = 10 X 0.8.
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149
the other. The samples were extracted and cleaned up as described for
the analysis of sulfur-containing pesticides in alfalfa.
The recoveries that were obtained are presented in Table XL.
Recoveries ranged from 65% for CIPC and simazine at 0.01 ppm to 101%
for PCNB at; 0.02 ppm. There did not appear, to be any distinct correlation
between the quantity of pesticide recovered and the level at which the
samples were fortified.
As shown in Figures 68 and 69, there are several peaks from the alfalfa
that can Interfere with the analysis of nitrogen compounds at the 0.01 to
0.0? ppm level. The interference peak between trifluralin and IPC exhibited
considerable variability, whereas the interference peak after PCNB was fairly
consistent. The interference peaks at the same retention times of atrazine
and simazine were also fairly constant, and were equivalent to approximately
0.002 ppm of these pesticides.
-------
150
Table XL. Recovery of Nitrogen-Containing Pesticides from Alfalfa.
Compound
CIPC
Atrazine
Simazine
Trifluralin
IPC
PCNB
% Recovery3
0.01 ppm 0.02 ppm 0.1 ppm
65 — 73
81 -- 78
65 -- 72
82 79
92
101 97
1 .0 ppm
76
82
80
74
70
74
10.0 ppm
77
94
90
88
81
83
Recoveries; are the average of three replicates.
-------
T i me (m i n.)
Figure 68. Chromatograms of CIPC (1), atrazine (2) and simazine (3)
extracted from alfalfa. Sample: A, control, attenuation
3 X 0.2; B, 0.01 ppm, attenuation = 3 X 0.2; C, 1 ppm,
attenuation = 100 X 0.2.
-------
s-
>
E
(0
c
o
Q.
0)
0)
c
Ul
Time (mi n.)
Figure 69. Chromatograms of tn'fluralin (1), IPC (2) and PCNB (3)
extracted from alfalfa. Sample: A, control, attenuation
10 X 0.1; B, 0.02 ppm, attenuation = 10 X 0.1; C, 1 ppm,
attenuation = 10 X 1.6.
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153
RECOMMENDED OPERATING CONDITIONS
AND MAINTENANCE
The electrolytic conductivity detector can be used for the selective
detection of halogen-, sulfur-, nitrogen- and ester-containing compounds.
It can also be used for the general detection of organic compounds and
the selective detection of certain compounds in the presence of other
compounds that contain the same element (such as nitrosamines in the
presence of other nitrogen compounds and aliphatic chlorine compounds
in the presence of aromatic chlorine compounds ). Response to a given
element depends upon the specific operating conditions employed. However,
the same conditions are not necessarily optimum for both sensitivity
and specificity. Thus, the utilization of generalized operating parameters
for a given element may not be sufficient for certain analyses.
Although a given set of operating parameters may not be sufficient
for all analyses, certain operating procedures provide superior detector
performance. For instance, nickel tubing and soxhlet extracted ion
exchange resins are recommended for the detection of halogen and sulfur
compounds. Stacked ion exchange resin beds are recommended for the
maintenance of a pH below 7.0 for halogen and sulfur compounds and
above a pH of 7.0 for nitrogen compounds. Specific operating conditions
for the detection of halogen-, sulfur-, and nitrogen-containing compounds
are listed below.
Detection of Halogen Compounds. Slightly different operating
parameters are recommended for a) the general detection of halogen-
containing compounds with maximum specificity, b) the general detection
of halogen-containing compounds with maximum sensitivity and peak sharpness,
-------
154
c) selective detection of aliphatic chlorine compounds in the presence of
aromatic chlorine compounds with maximum selectivity to chlorine, and
d) selective detection of aliphatic chlorine compounds in the presence
of aromatic chlorine compounds with maximum sensitivity and peak sharpness
General Detection of Halogen Compounds with Maximum
Specificity:
Reaction Tube3: Nickel (1/16 in. o.d. x 0.02 in. i.d.)
Reaction Gas: Electrolytic hydrogen
Reaction Gas Flow Rate: 100 cc/min.
Carrier Gas: High purity helium
Furnace Temperature: 840 - 860°
Conductivity Solvent: jT-Butyl alcohol
Conductivity Solvent Flow Rate: 0.6 cc/min.
Ion Exchange Resin : 65% IRN-77 on pump side
and 35% IRN-150 on cell side
of resin tube
Injection Solvent Vent: Yes
Interfering Elements: Negative peaks from large
quantities of nitrogen compounds.
aNickel reaction tube will take at least two days
to condition and may take as long as 10 days.
Resins soxhlet extracted with water and methyl alcohol.
-------
155
General Detection of Halogen Compounds with Maximum
Sensitivity:
Reaction Tube: Nickel (1/16 in o.d. x 0.02 in. i.d.)
Reaction Gas: Electrolytic hydrogen
Reaction Gas Flow Rate: 100 cc/min.
Carrier Gas: Electrolytic hydrogen or high purity
helium
Furnace Temperature: 840 - 860°
Conductivity Solvent: Methyl alcohol
Conductivity Solvent Flow Rate: 0.4-0.6 cc/min.
Ion Exchange Resin: 65% soxhlet extracted IRN-77
on pump side and 35% soxhlet extracted
IRN-150 on cell side
Injection Solvent Vent: Yes
Interfering Elements: Large quantities of nitrogen-,
sulfur- and ester-containing
compounds may give interference
Selective Detection of Aliphatic Chlorine with Maximum
Specificity to Chlorine:
Reaction Tube: Nickel (1/16 in. o.d. x 0.02 in. i.d.)
Reaction Gas: Air
Reaction Gas Flow Rate: 100 cc/min
Carrier Gas: High purity helium
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156
Furnace Temperature3: 750 - 800°
Conductivity Solvent: n-Butyl alcohol
Conductivity Solvent Flow Rate: 0.6 cc/min.
Ion Exchange Resin: 65% soxhlet extracted IRN-77
on pump side and 35% soxhlet
extracted IRN-150 on cell side
Injection Solvent Vent: Yes
Interfering Elements: Sulfur compounds and large
quantities of certain
nitrogen containing compounds.
Selective Detection of Aliphatic Chlorine with Maximum
Sensitivity.
Reaction Tube: Nickel (1/16 in. o.d. x 0.02 in. i.d.)
Reaction Gas: Air
Reaction Gas Flow Rate: 100 cc/min.
Carrier Gas: High purity helium
Furnace Temperature: 780 - 800°
Conductivity Solvent: Methyl alcohol
Conductivity Solvent Flow Rate: 0.4-0.6 cc/min.
Ion Exchange Resin: 65% soxhlet extracted IRN-77
on pump side and 35% soxhlet
extracted IRN-150 on cell side
Injection Solvent Vent: Yes
Interfering Elements: Sulfur compound and large quantities
of certain nitrogen- and ester-
containing compounds
aThe lower temperature results in greater selectivity, but may greatly
reduce response to certain aliphatic chlorine compounds.
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157
Detection of Sulfur-Containing Compounds. The following operating
parameters are recommended for the detection of sulfur-containing compounds.
Reaction Tube: Nickel (1/16 in. o.d. x 0.02 in. i.d.)
Reaction Gas: Air
Reaction Gas Flow Rate: 100 cc/min.
Carrier Gas: High purity Helium
Furnace Temperature: 650 - 800°
Conductivity Solvent: Methyl alcohol
Conductivity Solvent Flow Rate: 0.4-0.6 cc/min.
Ion Exchange Resin: 65% soxhlet extracted IRN-77
on pump side and 35% soxhlet
extracted IRN-150 on cell side
Injection Solvent Vent: Yes
Interfering Elements: Chlorine and large quantities
of certain nitrogen- and ester-
containing compounds
Two furnace temperatures are recommended. A furnace temperature of 650
gives the best selectivity and only certain types of halogen, nitrogen and
ester compounds will interfere. However, sensitivity at 650° is only 25
to 40% of that at higher temperatures. Consequently, a furnace temperature
of 800 is recommended for greater sensitivity but less specificity.
Detection of Nitrogen Compounds. Although only one set of conditions
is recommended for the detection of nitrogen compounds, certain modifications
of operating parameters may be required. For instance, if there is
contaminant bleed into the furnace that results in acidic reaction products,
-------
158
a small amount of nitrogen (0.01 to 0.1 cc/min.) may have to be added
to the reaction gas to compensate for the elevated acidity. The
recommended operating conditions are:
Reaction Tube: Quartz (1/8 in. o.d. x 2 mm. i.d.)
Catalyst: Nickel wire strands (0.12 mm. or 0.25 mm. o.d.
x ~ 1 in.)
Reacting Gas: Electrolytic hydrogen
Reaction Gas Flow Rate: 60 - 80 cc/min.
Carrier Gas: Electrolytic hydrogen or ultra-high
purity helium.
Furnace Temperature: 820 - 850°
Conductivity Solvent: 15% Isopropyl alcohol
Conductivity Solvent Flow Rate: 0.4-0.6 cc/min.
Ion Exchange Resin; 70% IRN-78 or ARA-366 and 30% IRN-150
Scrubber: 10% Sr(OH) on glass wool
Scrubber Position: Just within furnace end plate
Injection Solvent Vent: yes
Interfering Elements: Large quantities of sulfur
compounds
Detector Maintenance. In general, the only maintenance required
for the detection of halogen and sulfur compounds is a) replenishment of
the conductivity solvent, b) replacement of the conductivity solvent
approximately once a month, and c) replacement of the ion exchange resin
approximately every three to six weeks. The Teflon transfer lines and
conductivity cell usually do not become contaminated, but should be
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cleaned with H-PO. if contamination is suspected.
The detection of nitrogen compounds requires a) replenishment of
the conductivity solvent, b) replacement of the conductivity solvent
approximately every two weeks, c) replacement of the scrubber as required,
usually every two to four weeks for residue analyses, and d) replacement
of the ion exchange resin approximately every three months. The catalyst
usually lasts for six months to a year, but can be poisoned by column
bleed and other contaminants. Thus, the catalyst may require more frequent
replacement.
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Literature Cited
1. R. C. Hall, J. Chromatog. Sci.,12, 152 (1974).
2. D. M. Coulson, Am. Lab., 22 (May 1969).
3. W. P. Cochrane, B. P. Wilson and R. Greenhalgh, J. Chromatog.
75, 207 (1973).
4. G. G. Patchett, J. Chromatog. Sci.,£, 155 (1970).
5. B. P. Wilson and W. P. Cochrane, J. Chromatog., KI6, 174 (1975).
6. J. W. Rhoades and D. E. Johnson, J. Chromatog. Sci., 8>, 616 (1970),
7. J. W. Dolan and R. C. Hall, Anal. Chem., 45, 2198 (1973).
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/1-76-Q12
4. TITLE AND SUBTITLE
Optimization and Evaluation of a Microelectrolytic
Conductivity Detector for the Gas Chromatographic
Determination of Pesticide Residues
3. RECIPIENT'S ACCESSIONING.
5. REPORT DATE
January 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Dr. Randall C. Hall
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Entomology
Purdue University
West Lafayette, Indiana 47907
10. PROGRAM ELEMENT NO.
1EA488
11. CONTRACT/GRANT NO.
68-02-1703
1C. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park. N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY MOTES
16. ABSTRACT
A microelectrolytic conductivity detector has been optimized and evaluated for
the determination of halogen, nitrogen, and sulfur-containing pesticide residues
in water, soil and biological samples. The influence of detector operating
parameters on detector sensitivityand specificity to model compounds was
investigated. Specific parameters studied included furnace temperature, reaction
gas, reaction gas flow-rate, conductivity solvent, conductivity solvent flow-rate,
reactor contact material, and abstracting agents. Detection limits of represen-
tative pesticides were determined for a variety of sample types using optimized
detector operating conditions.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pesticides
Detectors
Gas Chromatography
Monitors
Water analysis
Soil analysis
Tissues CMology)
14 B, D
07 A
8. DISTRIBUTION STATEMENT
REJ.EASE. TO
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
164
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
161
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