Environmental Monitoring Series
IMPROVED TEMPERATURE STABILITY
OF SULFUR DIOXIDE SAMPLES COLLECTED
BY THE FEDERAL REFERENCE METHOD
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
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This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
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This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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IMPROVED TEMPERATURE STABILITY OF SULFUR DIOXIDE SAMPLES
COLLECTED BY THE FEDERAL REFERENCE METHOD
by
Robert G. Fuerst
Quality Assurance Branch
Environmental Monitoring and Support Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
QUALITY ASSURANCE BRANCH
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
SEPTEMBER 1977
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and
Support Laboratory, U.S. Environmental Protection Agency, and approved
for publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
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ABSTRACT
This report describes an examination of the reagents present in the S02
Federal Reference Method (FRM) to determine if any change in reagent concen-
tration or condition could bring about substantial, if not complete, retarda-
tion of the effect of temperature on the stability of collected S02 samples.
The parameters initially evaluated were pH, tetrachloromercurate
(TCM), and chloride ion concentration. With the development of a modified
i i
collecting solution based on these studies (0.04M TCM with a [Hg ] to
[Cl~] of 1/16), collection efficiency and order of reaction of the modified
collecting reagent were determined.
Using an Arrhenius plot of the experimental data, an equation was
derived which describes the relationship between rate of decay of collected
Stk samples and temperature. The modified collecting reagent was found to
increase the stability of the collected SCu samples over a wider temperature
range. Thus the effect of temperature was reduced by about 10°C when com-
pared against previous S0? FRM data. The improvements developed here could
be used to liberalize the present temperature specification required to
insure the stability of collected S02 samples.
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CONTENTS
Abstract ii
List of Figures iv
List of Tables v
Acknowledgments vi
1. Introduction 1
2. Experimental 2
3. Results and Discussion 4
4. Conclusions 20
5. Recommendations 31
References 32
m
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LIST OF FIGURES
Number Page
1 S02 in TCM equlibrium equations 5
2 Effect of pH and TCM concentration on stability
o
of the dichlorosulfitomercurate complex; pH = 3, 50 C . . . 9
3 Effect of pH and TCM concentration on stability
o
of the dichlorosulfitomercurate complex; pH = 5, 50 C . . . 10
4 Effect of varying the ratio of CHg^l/ECl"] on
the stability of the dichlorosulfitomercurate
o
complex; 50 C 14
5 Effect of varying the ratio of [Hg++J/[CT] on
the stability of the dichlorosulfitomercurate
complex; 50°C 15
6 Effect of temperature on stability of the modified
dichlorosulfitomercurate complex, 50°C 20
7 Effect of temperature on stability of the modified
dichlorosulfitomercurate complex, 40°C 21
8 Effect of temperature on stability of the modified
dichlorosulfitomercurate complex, 30°C 22
9 Effect of temperature on decay rate constant of
dichlorosulfitomercurate complex 26
iv
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LIST OF TABLES
Number Page
1 Effect of pH and TCM Concentration on Wavelength
Maximum and Time of Full Color Development, pH 3
and pH 5 8
2 Summary Effects of pH and TCM Concentration on
Stability of Dichlorosulfitomercurate Complex,
pH 3 and pH 5, 50°C 11
3 Effect of Varying the Ratio of [Hg++]/[Cl"] on Wavelength
Maximum and Time of Full Color Development 13
4 Summary Effects of Varying Ratio [Hg++]/[CT];
[Kg**] = 0.04 or 0.1 M, 50°C 16
5 Collection Efficiency of the Modified Reagent, 0.04 M,
[Hg++]/tCT] = 1/16 18
6 Comparison of the Temperature Stability of the
Dichlorosulfitomercurate Complex, FRM vs. Modified 20
7 Determination of Order and Reaction Rate 24
8 Effects of Temperature Experienced on
Spring and Summer Days on the Overall Decay
Rate of the FRM and the Modified Reagent 27
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ACKNOWLEDGMENT
The author wishes to thank Dr. Randy Korda of the State of Wisconsin,
Department of Natural Resources, Madison, Wisconsin, who suggested the
idea for this project.
vi
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SECTION 1
INTRODUCTION
Previous research (1-9) has indicated that samples collected by the
Federal Reference Method (FRM) for Determination of Sulfur Dioxide
Concentration in the Ambient Air(lO) have temperature dependent stability
problems both during and after sampling. To minimize this instability
problem several suggestions have been proposed:
(a) relocation of the present sampling site to a temperature
controlled structure,
(b) redesign of the sampler and shipping container to maintain
certain sample temperature specifications both during and prior to the
time of analysis (i.e., thermoelectric coolers, temperature controlled
shipping containers),(11)
(c) the use of continuous monitors; and
(d) stabilization of the formed dichlorosulfitomercurate complex
by adjusting the reagent concentrations and conditions.
In an attempt to minimize the cost suggested by (a), (b), and (c),
an investigation was begun to reduce the temperature dependent decay of
the formed complex to its minimum while keeping the reagents the same.
To evaluate the other alternatives would require an extended time period
for a full scale research project which would not meet our intended
purpose of a short-time solution. The results of these experiments to
adjust reagent concentration are discussed in this report.
1
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SECTION 2
EXPERIMENTAL
The specific reagents and procedures used for sample preparation and
analysis are those specified in the Federal Register for the determination
of S02 concentration in the atmosphere (Pararosaniline Method) (10). Other
pertinent experimental details not contained in that procedure are described
in the following sections:
SAMPLE PREPARATION
Unless otherwise described, all samples containing sulfur dioxide
($02) were prepared using the indicated tetrachlormercurate (TCM) and
sodium metabisulfite concentrations.
During the collection efficiency studies, two different S0«
permeation tubes (National Bureau of Standards, Standard Reference
Material #1627, 2 cm in length) were used to generate the test at-
mospheres using typical generation apparatus (10).
SAMPLE ABSORBING REAGENT PREPARATION
All TCM concentrations were prepared as described in the report
i I
with the nominal TCM concentration being 0.04 M with a [Hg ]/[Cl~]
ratio of 1/4.
SAMPLE TEMPERATURE CONTROL
The indicated temperatures of the experimental samples were maintained
by placing each sample in a constant temperature bath with the temperature
-------
of each maintained to + 0.1°C. This was accomplished by submerging the
capped sample below the solution volume line.
SAMPLE ANALYSIS
At selected times, portions of the thermostated samples were taken
and rapidly cooled to 22.0°C in a constant temperature bath to prevent
further decay before analysis. An aliquot (10 ml) of each of these portions
was taken and analyzed immediately for S02 concentration by the S02 Federal
Reference Method (FRM). A larger sample aliquot than that specified in
the FRM (5 ml) was taken because previous experiments conducted in our
laboratory indicated that much better precision and accuracy were obtained
at lower S02 concentrations by increasing the aliquot size. The temperature
at which the color was developed in the analytical procedure was also 22.0°C.
DATA ANALYSIS
Best fit regression analysis equations were calculated using a
programmable calculator-plotter.
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SECTION 3
RESULTS AND DISCUSSION
When ambient S02 dissolves in an aqueous solution containing mercuric
chloride, potassium chloride, and ethylenediaminetetraacetate disodlium salt
(EDTA) of specified proportions, several equilibriums (12-13) are established,
the major ones being shown in Figure 1. The equations show that sulfur
dioxide is present in three different forms before a complex is formed:
(a) sulfurous acid;
(b) bisulfite ion;
(c) sulfite ion.
At a pH of approximately 4, which is the pH of the S02 FRM absorbing
reagent, the major species found is the bisulfite ion. This is the
species that complexes with the tetrachloromercurate to form the dichloro-
sulfitomercurate complex. Although a small concentration of SOZ is in
equilibrium, oxidation of this species is thought to be the cause of loss
of S02, since the formation of SO^ is not reversible. This causes a constant
equilibrium condition to be established at the expense of the bisulfite ion
and continuously depletes the concentration of bisulfite available to be
complexed by the tetrachloromercurate. Another problem with the TCM is its
ionization in dilute solutions(5) which reduces pH and lowers collection
efficiency.
Possible solutions to these problems are:
(a) reducing the amount of SO^ formed by controlling pH and making
4
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(H2S03> pK=1.8 pK=6.9
[H20-S021 3=+. [H+] + [HS03] «*—> 2[H+] + [803 1
01
HgCI2 + 2KCL =fcq»: K2HgCI4 [0]
t I
2[H+] + 2[CL- ] + K2HgCI2S03 [$04 ]
Figure 1. SO2 in TCM equilibrium equations.
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the HSOg the most favorable species;
(b) increase the amount of TCM available as a complexing agent
by decreasing the ionization of the TCM by:
1. increasing the TCM concentration, and
2. increasing the Cl~ ion concentration.
The other reagents used in the analytical procedure of the S02 FRM
could be examined for the effect on decay, but drastic changes in reagent
makeup, even if successful, would entail lengthy evaluations and equiva-
lence studies which would preclude a short time solution. If a need does
exist to significantly alter the current method or to develop a new method,
research oriented groups must continue these projects.
EFFECT OF pH AND TCM CONCENTRATION
Previous studies indicate that the optimum pH of the S02 FRM absorbing
reagent is 4.0 + 1. (5)(15) The studies show that optimum color can be
developed and that collection efficiency was not adversly affected in this
range. As the pH of the solution becomes less than 2, the S02 becomes less
soluble in the solution, and the excess S02 will be flushed out by the air
bubbling through the sampling system. Above a pH of 7 the equilibrium will
favor more SOZ formation, which could result in eventual loss as sulfate.
To examine the effect of pH, solutions were prepared at pH = 3 and
pH = 5. Four concentrations of TCM (0.01, 0.04, 0.1, and 0.25 M) were ex-
amined at each pH. The pH was adjusted with HC1 or NaOH dropwise and the
pH measured with a calibrated pH meter.
3
A simulated S02 sample concentration of 165 yg S02/m (using a sulfite
standard solution containing 0.95 yg S02/ml and an assumed sampling rate of
200 cc/min for 24 hours using 50 ml of absorbing reagent) was used as the
sample.
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This concentration was chosen because it is approximately twice the
primary SCL arithmetic mean standard and about one half the maximum 24
hour concentration(lO).
Before subjecting these samples, with their specific absorbing
reagents, to a temperature study, basic information such as wavelength
maximum and color development time for the solutions had to be determined.
These data are shown in Table 1.
Since these samples showed full color development in 30 minutes
this was the time selected for these samples.
Figures 2 and 3 for pH 3 and 5, respectively, show the effect of
o
50°C on the same concentration (165 yg SOp/m ) prepared in 0.01, 0.04,
0.1, and 0.25 M TCM. The curves indicate that as the TCM concentration
increases, the rate of decay of the SOo concentration decreases, and as
the TCM concentration increases the y-intercept, which indicates sensi-
tivity, decreases. (No further study to describe the actual sensitivity
of the method or any of its modifications was continued). Table 2 summarizes
the effect of pH 3 and 5. No significant difference in decay rate was found
between the results of pH 3 and 5. Although at 0.25 M TCM pH = 3, the decay
rate reached a minimum of 41 percent per day, a substantial increase in TCM
concentration was necessary with the associated problem of disposal of larger
quantities of mercury when the reagent is spent.
EFFECT OF INCREASE OF CHLORIDE ION
It was originally reported (14) that the most stable dichlorosulfito-
mercurate complex was formed when the ratio of [NaCl] to [HgCl^J was equal
to 2. This gave a [Hg ] to [Cl~] ion concentration of 1 to 4. This was al-
so found to be the case when Scaringelli modified(15) the West-Gaeke pro-
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TABLE 1. EFFECT OF pH and TCM CONCENTRATION ON WAVELENGTH MAXIMUM
AND TIME OF FULL COLOR DEVELOPMENT
Concentration
pH 3
pH 5
0.01 M TCM
0.04 M TCM
0.1 M TCM
0.25 M TCM
0.01 M TCM
0.04 M TCM
0.1 M TCM
0.25 M TCM
X Max
548 nm
548 nm
548 nm
555 nm
548 nm
548 nm
548 nm
555 nm
Time of Max Color
15-45 min
15-60 min
15-60 min
15-60 min
30-60 min
15-60 min
15-60 min
15-60 min
-------
0.300
0.240
0.180
DO
DC
O
CO
0.120
0.060
Y = 0.334e '5-07x
0.01M TCM
0.22
0.88
0.44 0.66
TIME, day
Figure 2. Effect of pH and TCM concentration of stability of the dichlorosulfitomercurate complex, pH = 3, 50°C.
1.1
-------
0.30ft
0.240
0.180
u
z
ca
GC
O
ta
0.120
0.060
Y = 0.266e-°-62x
0.25 M TCM
0 0.2 0.4 0.6 0.8 1.0
TIME, days
Figure 3. Effect of pH and TCM concentration on stability of the dichlorosulfitomercurate complex, pH=5, 50°C.
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TABLE 2. SUMMARY OF THE EFFECTS OF pH AND TCM CONCENTRATION ON STABILITY OF THE
DICHLOROSULFITOMERCURATE COMPLEX, 50°C
(Y = AeBX)
1
TCM
CONC.
0.01 M
0.04 M
0.1 M
0.25 M
A
0.334
0.297
0.283
0.268
pH =
B
-5.07
-1.46
-0.79
-0.52
3
Percent Decay
Day
99+
77
55
41
pH = 5
A
0.316
0.286
0.280
0.266
Percent Decay
B Day
-5.71 . 99+
-1.55 79
-0.83 56
-0.62 46
X = Time, Days
Y = Sample Absorbance
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cedure, which is the procedure used as the S02 FRM. To »eexamine the
temperature stability of the formed complex at various ratios of [Hg++]
to [Cl~], standard solutions were prepared using a 165 yg S02/m3 static
standard. These solutions were then subjected to a temperature of 50°C.
Two concentrations of [Hg ] were used, 0.04 M (nominal) and a 0.1 M.
Table 3 indicates the results of preliminary experiments for wavelength
maximum and time of full color development. The results of the stability
experiments are shown in Figures 4 and 5. A summary of these stability
experiments is shown in Table 4. Both the 0.04 M and the 0.1 M [Hg++]
concentration experiments indicate that as the [Cl~] concentration
increases in the ratio of [Hg++]/[Cl"] from 1/2 to 1/32, the rate of
decay of the sample concentration decreases to a minimum of about
19 percent and 14 percent per day, respectively.
ii
The 0.04 M [Hg ] concentration reaches an optimum absorbance
around 1/3 to 1/4, which is the nominal; from there on the y-inter-
cept decreases, indicating a loss in sensitivity. Also the 0.1 M [Hg ]
solutions give a higher sensitivity for each ratio, indicating a
suppressing of color by the more [Hg ] concentrated solution. Based on
these experiments the most stable complex is formed when the ratio of
[Hg++]/[Cl~] concentration is 1/16 at a [Hg++] concentration of 0.04 M.
Although the 0.1 M [Hg"1"1"] 1/8 and 1/16 solutions gave slightly better
stability to temperature, the amount of [Hg++] present and hence the
amount to be disposed of was thought to be detrimental.
12
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TABLE 3. EFFECT OF VARYING THE RATIO OF [Hg++]/[CT] ON WAVELENGTH MAXIMUM AND TIME OF
FULL COLOR DEVELOPMENT
0.04 MtHg"1"*]
[Hg++]
ccn
1/2
1/3
1/4
1/8
1/16
1/32
MAX
548 nm
548 nm
548 nm
550 nm
556 nm
556 nm
TIME
30
15
15
15
15
15
OF MAX COLOR
- 60 Min.
- 60 Min.
- 60 Min.
- 60 Min.
- 60 Min.
- 30 Min.
O.TMTH^]
1/4
1/8
1/16
1/32
548 nm
555 nm
555 nm
570 nm
15
15
15
15
- 60 Min.
- 45 Min.
- 45 Min.
- 45 Min.
-------
0.300
0.241
0.180
CO
cc
o
en
0.120
0.060
0.000
[HgTT]/[Cr] =1/8,0.04 M [Hg
[Hg-H-]/[C|-]=1/8,0.1M[Hg
[Hg"-]/[C|-] = 1/3,0.04 M[Hg-"1
I/Id'] = 1/2,0.04M [Hg**]
1.0
Figure 4. Effect of varying the ratio of [Hg"1"*] /[Cl~] on the stability of the dichlorosulfitomercurate
complex; 50°C.
-------
0.180
0.144
0.108
CQ
cc.
o
0.072
0.000
0.036
0.00
7.10
Figure 5. Effect of varying the ratio of [Hg++] /[Cl~] on the stability of the dichlorosulfitomercurate
complex; 50°C.
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TABLE 4. SUMMARY EFFECTS OF VARYING RATIO [Hg++]/[cr], [Hg"1"1"] = 0.04 or 0.1 M, 50°C
a\
CHtt
[CT]
1/2
1/3
1/4
1/8
1/16
1/32
0.4 M
A B
0.267 'FAST
0.295 -1.60
0.291 -1.47
0.263 -0.43
0.231 -0.21
0.160 -0.26
(Y = AeBX)
Percent Decay
Day
100
80
77
35
19
23
Percent Decay
A B Day
0.283 -0.79 55*
0.233 -0.15 14
0.181 -0.20 18
0.139 -0.27 24
X = Time, Days
Y = Sample Absorbance
* at a pH = 3
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COLLECTION EFFICIENCY
Before going into a more detailed temperature study, the ability of this
modified solution (0.04 M TCM, [Hg++]/[Cl"] = 1/16) to collect S02 had to be
determined. Two different SRM permeation tubes were used at different times
to generate test atmospheres and were sampled with five bubbler trains in
parallel for 24 hours at approximately 0.23 1/min. Initial sampling (Room
Temperature) indicated plugging of the glass bubbler (narrow drawn tip with
orifice of approximately 0.37 mm) during the 24 hour period in three out of
five trains. The plugging was caused by a buildup of salts on the inside of
the orifice tip. This experiment was repeated with the same results. The
glass bubblers were then removed and replaced with identical lengths of 6 mm
i.d. Teflon^-' tubing. No more plugging was experienced throughout the course
of the experiments. The size of the orifice tip must be optimized in a typi-
cal sampling system before general use is made using the modified reagents.
Because the original experiments indicated a decrease in sensitivity, the
sample aliquot was changed to 15 ml. No-reagent concentration in the analysis
part of the FRM was changed. The results of these experiments are listed in
Table 5. The overall collection efficiency was observed to be 88.5 +_ 3.4 per-
cent. This shows a decrease in collection efficiency of about 11 percent from
the 100 percent efficiency reported when using the FRM. This collection effi-
ciency might be optimized using various size orifices to create more surface
area on each air bubble.
EFFECT OF TEMPERATURE ON THE MODIFIED REAGENT
Five different sets of solution samples were prepared from Na2S2Or in the
modified absorbing reagent to simulate ambient concentrations of 0, 49, 82,
3
163, and 359 yg S02/m . Each set of solutions was exposed to temperatures of
20°, 30°, 40°, or 50°C on a continuous basis. From previous experiments it was
^trade name
17
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++
TABLE 5. COLLECTION EFFICIENCY OF THE MODIFIED REAGENT, 0.04 M [Hg],
= 1/16
00
TUBE NO. 1
yg S02 Percent ug S02
m3 Recovered 3
36.8 93.0+3.8* 39.2
36.9 86.4+6.8* 84.3
167.0 86.5+3.5* 178.0
417.0 90.6+4.0* 410.0
x = 89.1 +4.5
OVERALL
x = 88.5 +_ 3.4
TUBE NO. 2
Percent
Recovered
90.5 +2.8*
86.8 + 1.4*
85.2 + 3.0*
88.8 +1.7*
x = 87.8 +2.2
*Standard Deviation of 5 Different Sample Results.
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determined that when samples, using modified reagent, were kept at 5°C for up
to 36 days no decay was detected. A set of these samples plus one standard
at 124 yg SO^/m was used as a standard curve; each time a set of samples was
analyzed a standard curve generated from a set stored at 5°C was used as a
reference.
Portions of the thermostated samples were taken and rapidly cooled to
22°C. A 15 ml aliquot was analyzed according to the analytical procedure
specified in the S02 FRM, and the results plotted using a best fit regression
curve (Figures 6, 7 and 8). No plot was made of the samples exposed to 20°C,
because no decay was detected for up to 24 days. Of special note is that no
concentration effect was found on the rates of decay. Table 6 summarizes the
findings and compares them with our previous finding using the absorbing re-
agent specified in the S(L FRM(9). As can be seen from the summary, the rate
of sample concentration decay has been drastically reduced. The modified
collecting reagent has been found to increase the stability of the collected
SCL samples over a wider temperature range. Thus the effect of temperature
was reduced by about 10°C when compared against previous SCL FRM data.
ORDER OF REACTION
Because our data had a best fit exponential regression equation, first-
order or a quasi-first order reaction is suspected. An independent check
using the Van't Hoff equation verified this.
In V = In k + n In c
where v = velocity of reaction, total yg S02/day
k = rate of decay, day"
n = order of reaction, slope of line
c = concentration of sample, total yg S02-
19
-------
31.0
PO
o
27.9
24.8
21.7
18.6
CM
O
V)
15.5
12.4
0.0
1.6
2.4
5.6
6.4
7.2
3.2 4.0 4.8
TIME, day
Figure 6. Effect of temperature on stability of the modified dichlorosulfitomercurate complex, 50°C.
8.0
-------
31.0
0.0
1.3
2.6
9.1
10.4 11.7
5.2 6.5 7.8
TIME, day
Figure 7. Effect of temperature on stability of the modified dichlorosulfitomercurate complex, 40°C.
13.0
-------
28.8
25.6
22.4
19.2
ro
E
in
16.0
0.0
0.0
2.8
5.6
8.4
19.6
22.4
25.2
11.2 14.0 16.8
TIME, day
Figure 8. Effect of temperature on stability of the modified dichlorosulfitomercurate complex, 30°C.
38.0
-------
PO
CO
TABLE 6. COMPARISON OF THE TEMPERATURE STABILITY OF THE DICHLOROSULFITOMERCURATE COMPLEX
PERCENT DECAY/DAY
TEMP.
50°C
40°C
30°C
20°C
TRM TCM
74.
25.
5.0
0.9
MODIFIED TCM
20.
5.5
0.8
*
*No loss detected after 24 days
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These plots must give a straight line for this equation to estimate order of
reaction (Table 7).
ANNHENIUS EQUATION
To expand the usefulness of the temperature decay rate data use is made
of an Arrhenius plot. When the logarithm of the decay rate (k) is plotted
against the inverse of the absolute temperature, a linear relationship results
if the activation energy remains independent of the temperature.
k = Ae <-E/RT>
where k = rate of reaction (decay), day
A = frequency factor, day
E = energy of activation, calories/mole
R = gas constant, 1.987 calories/degree-mole
T = absolute temperature of reaction, K
Figure 9 is an Arrhenius plot of our data
|)
where In k = In A - ()
In k = 49.284 - 16385 (y).
The point k = 0.005, 30°C was deleted from the derivation of the equation
because of its own variable plot (Figure 8). To adequately describe the
effect at 30°C, a much longer time to allow measurable sample concentration
decay is necessary to overcome small variations in sample absorbance
readings.
From this equation rates of decay within the measured range and slightly
to the outside can be calculated with confidence. This equation also indi-
cates that the activation energy is equal to 32.6 kcal/mole. The activation
energy of the S02 FRM reaction was calculated to be 31.2 kcal/mole (9).
Increasing the [Cl~] concentration in the [Hg++]/[Cl"] ratio from 1/4 to
1/16 increases the energy of activation 1.4 kcal/mole.
24
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TABLE 7. DETERMINATION OF ORDER AND REACTION RATE
on
Temp
°C
50
40
30
Order
of
Reaction
0.9987
0.9860
1.103
In k
-1.508
-2.844
-5.082
Estimate
of
k
-0.221
-0.058
-0.006
-------
•1.40
ro
-2.20
a
3
S -3.00
H
£
cs
-3.80
4.60
-5.40
0.003080
i r
Ink = 49.284 -16385
0.003128
i
0.003176 0.003224
0.003272
TEMPERATURE 1C
Figure 9. Effect of temperature on decay rate constant of dichlorosulfitomercurate complex.
0.003320
I
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COMPARING THE EFFECT OF VARYING TEMPERATURE ON THE S02 FRM AND OUR
MODIFICATION
Using the mathematical model, we derived in a previous project (9),
a theoretical comparison of temperature effect on an ambient collected
sample experiencing a typical spring and summer day here at the Research
Triangle Park, N.C., was derived and shown in Table 8. This table quite
dramatically shows the decrease in decay that would be experienced if the
suggested modification were incorporated. However, these temperatures
reflect the ambient temperature, not the temperature inside a bubbler
box sampler.
GENERAL INFORMATION
(a) During the major temperature study, standard samples stored at
5°C were analyzed with the following results over a period of a month.
n = 12 R2 = 0.9992
average slope 0.0218
standard deviation +_ 0.0008
average blank measured 0.094 absorbance units
average y-intercept 0.089 absorbance units
A difference of measured blank and y-intercept of greater than 0.015
absorbance units indicated a significant difference between the two and
they could not be considered equal.
(b) As a check on the ability of the spectrophotometer to make a
consistent measurement, a Standard Reference Material 930c purchased from
the National Bureau of Standards consisting of one blank and three
neutral density filters were measured for absorbance over the periods of
analysis. Although the filters were calibrated by NBS at other wavelengths
they were measured at the wavelength of maximum absorbance (556 nm) as
27
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TABLE 8. EFFECTS OF TEMPERATURE EXPERIENCED ON SPRING AND SUMMER DAYS ON THE OVERALL
DECAY RATE OF THE FRM AND THE MODIFIED REAGENT
IN3
00
SPRING DAY
16 Hours 22°C (72°F)
4 Hours 25°C (77°F)
4 Hours 30°C (86°F)
FRM 2.2 Percent Decay
Day
MODIFIED 0.3 Percent Decay
Day
SUMMER DAY
16 Hours 22°C (72°F)
4 Hours 30°C (86°F)
4 Hours 35°C (95°F)
FRM 3.8 Percent Decay
Day
MODIFIED 0.6 Percent Decay
Day
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a quality assurance check. The three gave average (n = 16) values of
0.510 + 0.001, 0.722 + 0.001, and 1 .016 +_ 0.001 , indicating proper oper-
ation of the spectrophotometer during analysis.
(c) During the project it was noted that when the nominal formaldehyde
(HCHO) concentration (0.2 percent) was increased, the developed absorbance
decreased, and as the nominal HCHO concentration decreased, there was a
slight increase in absorbance.
HCHO CONCENTRATION
(Nominal = N)
PERCENT log ,Q7 ,
MEASURED 108 107 '
I)N (2x)N
100 83
(3x)N
74
The increase in HCHO concentration decreased the sample absorbance and
increased the absorbance of the blank; the reverse was also true.
BLANK ABSORBANCE
(Nominal = N)
(1/3)N
PERCENT R,
MEASURED OJ
(1/2)N (1)N
92 100
(2x)N
132
(3x)N
170
The age of the HCHO solution (0.2 percent) is also critical and should
be optimized if this modification is used. Preliminary experiments indicate
that the HCHO solution should be prepared immediately prior to addition. As
the age of the HCHO solution increased, the sensitivity of the measurement
decreased. Accuracy is not affected because all measurements would be
relative to a daily static calibration.
29
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SECTION 4
CONCLUSIONS
This project was undertaken for the purpose of determining if any
change in reagent concentration or condition in the S0? FRM could bring
about substantial retardation of the effect of temperature on the stability
of the formed complex. By increasing the amount of the chloride ion
([Hg ] = 0.04 M), we have essentially reduced the decay rate of the
formed TCM-SOp complex by an effect of 10"C. The improvement we have
developed here could be used to liberalize the sample temperature
specification required to protect the integrity of the collected S02
sample.
However, this modification does not erase all temperature speci-
fications for sample handling and if this modification is to.be used
routinely further optimization of some physical parameters (i.e., bubbler
tip size) must be accomplished.
30
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SECTION 5
RECOMMENDATIONS
Based on the temperature sensitivity of the S02 FRM both during sampling
and prior to analysis, certain temperature specifications(16) were recommended
to all Environmental Protection Agency Regions in their handling of the
24 hour SOp sample when using the Pararosaniline Method. It was suggested
that sampling be carried out in such a manner that the TCM absorbing reagent
be maintained at 25°C or less during sampling and that the collected
samples be maintained at 20°C or less until analysis.
What this effectively suggests is that during sampling and prior to
analysis the sample decay should not exceed one percent per day. Even though
the sample decay rate at 25°C is 2.4 percent per day (FRM), the whole amount
is not present at the beginning and the decay can best be estimated during
sampling to be one half of the decay of a collected sample that sat
at 25°C for 24 hours.
As indicated in this report, increasing the [Cl~] concentration in
the ratio of [Hg"1"1"] to [Cl~] from 1/4 to 1/16 (0.04M Hg"1"1") effectively re-
duces the temperature sensitivity of the formed complex by 10°C.
Therefore, maintaining the same decay rate specification as originally
suggested would mean a sampling temperature of 35°C or less and a shipping
and storage temperature of the collected sample not to exceed 30°C.
Although this drastically reduces the temperature control needed
on sampling and storage of the sample, it does not erase it completely;
some temperature control is still necessary.
31
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REFERENCES
1. McCaldin, R.O., and E.R. Hendrickson. J. Amer. Ind. Hyg. Assoc.,
20:509, 1959.
2. Perry, W.H., and E.G. Tabor. Arch. Environ. Health, 4:44, 1962.
3. Lahmann, E., Staub-Reinhalt. Luft, 29:30, 1969.
4. Groth, R.H., and D.S. Calabro. Presented at 63rd Annual Meeting Air
Pollution Control Association, St. Louis, MO., June 14-18, 1970.
5. Scaringelli, P.P., L. Elfers, D. Norris, and S. Hochheiser. Anal.
Chem. 42:1818, 1970,
6. Shinji, T., E. Kazuhiko, and K. Kazuma. Jpn. Anal. (Bunseki Kagaku),
20:1097, 1971.
7. Kasten-Schraufnagel, P., D.L. Ehman, and D.J. Johnson. Texas Air
Control Board Report, Air Quality Evaluation Division. Austin, TX.,
January 15, 1975.
8. Sweitzer, T.A. Presented at the 32nd Annual Meeting of the East
Central Section Air Pollution Control Association, Dayton, OH,
September 17-19, 1975.
9. Fuerst, R.G., F.P. Scaringelli, and J.H. Margeson. Environmental
Monitoring Series, EPA-600/4-76-024, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May 1976.
10. Federal Register 36 (84):8187-91, April 30, 1971.
11. Martin, B.E., Environmental Monitoring Series, EPA-600/4-77-040,
U.S. Environmental Protection Agency, Research Triangle Park,
NC, August 1977.
12. Terraglio, F.P., and R.M. Manganelli. J. Air Poll. Control Assoc.
17(6):403-06, 1967-
jji *
13. Huitt, H.A., and J.P. Lodge, Jr. Anal. Chem. 36:1305, 1964.
14. West, P.W., and G.C. Gaeke. Anal. Chem. 28(12):1816, 1956.
15. Scaringelli, F.P., B.E. Saltzman, and S.A. Frey. Anal. Chem.
39(14):1709, 1967.
32
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16. Clements, J.B. Memo to Directors, Surveillance and Analysis Division,
I to X, U.S. Environmental Protection Agency, Research Triangle Park,
NC, December 29, 1975.
33
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TECHNICAL REPORT DATA '
(Please read Instructions on [he reverse before completing)
. Rt.= ORT NO.
EPA-600/4-78-018
3. RECIPIENT'S ACCESSIOI»NO.
•;. TITLE AMD SUBTITLE
IMPROVED TEMPERATURE STABILITY OF SULFUR DIOXIDE
SAMPLES COLLECTED BY THE FEDERAL REFERENCE METHOD
5. REPORT DATE
February 1978
6. PERFORMING ORGANIZATION CODE
AUTHOaiSi
8. PERFORMING ORGANIZATION REPORT NO.
Robert G. Fuerst
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Quality Assurance Branch
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
1HD621
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report describes an examination of the reagents present in.the S0?
Federal Reference Method (FRM) to determine if any change in reagent concen-
tration or condition could bring about substantial, if not complete, retarda-
tion of the effect of temperature on the stability of collected S02 samples.
The parameters initially evaluated were pH, tetrachloromercurate
(TCM), and chloride ion concentration. With the development of a modified
collecting solution based on these studies (0.04M TCM with a [Hg ] to
[Cl~] of 1/16), collection efficiency and order of reaction of the modified
collecting reagent we^e determined.
Using an Arrhenius plot of the experimental data, an equation was
derived which describes the relationship between rate of decay of collected
S02 samples and temperature. The modified collecting reagent was found to
increase the stability of the collected S02 samples over a wider temperature
range. Thus the effect of temperature was reduced by about 10°C when com-
pared against previous S02 FRM data. The improvements developed here could
be used to liberalize the present temperature specification required to
insure the stability of collected SOP samples.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Held/Group
Air Pollution
Sampling
Temperature
Sulfur Dioxide
13B
13. I;l5THIBUTIGN STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS f This Report/
UNCLASSIFIED
21. NO. OF PAGES
33
20. SECURITY CLASS {Thispagel
UNCLASSIFIED
22. PRICE
EPA Farm 2220-1 (9-73)
34
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