600/A-98-049
Measurement of Carbonyl Compounds from Stationary
Source Emissions by a PFBHA-GC-ECD Method
98-RP105A.04 (A227)
Zh!-hua Fan, Max IL Peterson, and R.K.M. Jayanty
Research Triangle Institute, Research Triangle Park, NC 27709
Frank W.Wilshire
U.S. Environmental Protection Agency, Research Triangle Park, NC 27709
ABSTRACT
Carbonyl compounds have received increasing attention because of their important role in
ground-level ozone formation. Currently, there is no validated stationary source emission test
method for the measurement of carbonyl compounds, especially for the unstable carbonyls, such
as acrolein. This paper presents a study in the development of a test method for the measurement
of carbonyls from stationary source emissions. This method involves collection of carbonyls in
midget impingers, derivatization of carbonyls with 0-2,3,4,5,6-pentafluorobenzyl hydroxylamine
hydrochloride (PFBHA), separation of carbonyl-PFBHA derivatives by gas chromatography
(GC), and measurement of the derivatives with electron capture detection (ECD). Formaldehyde,
acetaldehyde, acrolein, acetone, butyraldehyde, methyl ethyl ketone, methyl isobutyl ketone, and
hexaldehyde were selected as candidates for the method evaluation.
The test gas containing the selected compounds was generated from either a certified gas
cylinder or permeation tubes. The retention and recovery efficiencies for the selected
compounds were tested using midget impingers filled with 20 mL of methanol or water. The
retention in the upstream impinger was > 85% for all the compounds tested using methanol as
the solvent, but the retention was < 70% for acetaldehyde and < 60% for acrolein, butyraldehyde,
and hexaldehyde when collected in water. The recovery efficiency (total mass collected in
upstream and downstream impingers) was > 80% for all the compounds tested using methanol as
the collection solvent, but the recovery efficiency was < 75% for butyraldehyde and hexaldehyde
using water as the solvent. Generally, larger variabilities of retention and recovery efficiencies
were observed when water was used as the collection solvent. When tested under the humid
condition (-10% water v/v), the presence of moisture appeared to have no effects on the retention
and recovery efficiencies for carbonyl compounds.
The stability of selected compounds was tested in both water and methanol. Degradation of
acrolein was observed in both solvents. In the presence of phenol, slow decay was also observed
for formaldehyde, acetaldehyde, and hexaldehyde in water, but no decay was observed for these
compounds in methanol. The addition of PFBHA stabilized acrolein in both water and methanol.
Formaldehyde, acetaldehyde, and hexaldehyde also became stable with the addition of PFBHA
in water with phenol presence. In addition, higher derivatization yields were obtained for
ketones in methanol. Similar derivatization yields were obtained for aldehydes in both solvents;
however, the aldehyde derivatives gradually dissociated in water after they formed.
Good detector response linearity was obtained for carbonyl-PFBHA derivatives (R2 > 0.99) over
the range of 0.04 - 2.5 jig/mL when analyzed by GC-ECD. The analytical detection limit was
-10 pg. This detection limit equates to -10 ng/L of carbonyls in a 20-L sample collected from
stationary source emissions.

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INTRODUCTION
Caibonyl compounds have received increasing attention because of their important role in
ground-level ozone formation.1,2 These compounds are generated from both primary and
secondary sources; they are directly emitted into the atmosphere from incomplete combustion3 as
well as being formed as an intermediate in the atmospheric photooxidation of hydrocarbons.1-
Because of their active roles in atmospheric chemistry, it is important to establish an accurate
measurement technique for these compounds.
Currently, there is no validated stationary source emission test method for the measurement of
carbonyl compounds, especially for the unstable carbonyl compounds, such as acrolein. This
paper-presents a study in the development of a test method for the collection and measurement of
caibonyls from stationary source emissions. This method involves collection of caibonyl
compounds in midget impingers, derivatization of caibonyls with 0-2,3,4,5,6-pentafluorobenzyl
hydroxylamine hydrochloride (PFBHA), separation of carbonyl-PFBHA derivatives by gas
chromatography (GC), and measurement of the derivatives by electron capture detection
(ECD)4*6. Both water and methanol were tested as the collection solvents, and the retention and
recovery efficiencies for carbonyls were compared for both solvents.
EXPERIMENTAL METHODS
Sampling
The sampling and analytical method for carbonyl compounds were evaluated in the laboratory.
Formaldehyde, acetaldehyde, acrolein, acetone, butyraldehyde, methyl ethyl ketone (MEK),
methyl isobutyl ketone (M3BK), and hexaldehyde were selected as the candidate compounds for
the method evaluation. A schematic diagram of the dynamic dilution system used for the test is
shown in Figure 1. Acrolein, acetone, MEK, M3BK, and hexaldehyde were generated from a
certified cylinder containing 14-21 ppm (v/v) of each compound (Scott Specialty Gases, Inc.,
Plumsteadville, PA), and butyraldehyde (-12 ppm) was generated from a 6-L stainless steel
canister prepared in the laboratory. Formaldehyde and acetaldehyde were generated with
calibrated permeation tubes heated in an oven at 100 ± 0.1 °C and 40 ± 0.1 °C, respectively. A
dynamic dilution Systran with a 1-liter dilution flask was used for mixing carbonyls with diluent
nitrogen. The flow rate of diluent nitrogen was 1.75 to 2.5 L/min, and the flow rate of the
cylinder containing carbonyls was 20 to 40 mL/min. This mixture produced a continuous supply
of gas containing carbonyl compounds at concentrations of200 to 400 ppb. The retention and
recovery efficiencies of caibonyls were also tested under humid condition. A test gas containing
-10% (v/v) of water was generated by adding a humidified gas stream to the gases entering the
dilution flask. Water condensation would be expected to occur in the impinger with test gas
containing 10% (v/v) of water, and the effects of water condensation on the recovery efficiencies
for carbonyl compounds could thus be tested.
The gas mixture was passed from the dilution flask to a three-port manifold, and the carbonyl
compounds were collected in two midget impingers connected in series. A Teflon tube (1/4"
OD) was used to connect the sampling port and the upstream impinger, and the Teflon line was
wrapped with heating tape to prevent the condensation of the sample stream on the sampling line.
Each impinger was filled with 20 mL of water (Milli-Q organic-free water) or methanol (Purge
• and Trap grade, Aldrich Chemical Co., Milwaukee, WI). The impingers were immersed in an ice
bath during the sampling period. A drierite was connected between the downstream impinger
1

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and the sampling pump to absorb water vapor in the sample stream. A schematic diagram of the
sampling train is shown in Figure 2. The sampling flow rate was -1.0 L/min, and the collection
time was 20 minutes. Tylan mass flow controllers were used to regulate the flow rate. After
sample collection, the sample was diluted with water or methanol, as appropriate, to a 25 mL
volume before derivatization.
Sample Derivatization
Caibonyl compounds were derivatized by PFBHA (Aldrich Chemical Co., Milwaukee, WI) and
measured by a GC-ECD. The PFBHA (5 mg/mL) was prepared in Milli-Q organic-free water.
After sample collection, an aliquot (2-5 mL) was taken from the impinger and placed in a second
vial. To determine reaction and extraction efficiency of the cafbonyls, ten nL of 100 jig/mL
2,3,5,6-tetrafluorobenzaldehdye (TFB) surrogate additive standard was added to the sample
before derivatization. Subsequently, PFBHA was added in the amount of 0.1 mL of 5 mg/mL to
the sample. The amount of PFBHA added to the sample was -10-fold molar excess, which
enhanced derivatization yields. The vial was sealed and shaken for - 30 seconds and the mixture
was allowed to react for 24 hours at room temperature. Three drops of 37% hydrochloric acid
were then added to acidify the mixture. Most of the unreacted PFBHA remained in the acidic
aqueous phase during the subsequent extraction. The derivatives were extracted with 2 mL of
optima grade hexane containing 0.4 jig/mL of 1,2-dibromopropane as an internal standard.
When methanol was used as the collection solvent, 1 mL of water was added to the mixture
before extraction to obtain better separation between methanol and hexane. Also, a second
extraction of the methanol fraction was performed with 1 mL of pure hexane. The top layer of
hexane was transferred to another vial with a Pasteur pipet and analyzed by a GC-ECD.
Instrumentation and Analytical Methods
Carbonyl-PFBHA derivatives were analyzed on a Hewlett Packard 5890 GC equipped with an
ECD. The GC column used for derivatives separation was a 60-m length, 0.32-mm ID, 1.0-jim
film thickness, SPB-1 fused silica column (Supelco, Inc., Bellefonte, PA). The column carrier
gas flow rate was 2 mL/min. A split/splitless injector was used for this study, and the split ratio
was 1:35. The injector temperature was 250 °C, and the detector temperature was 280 °C. Initial
oven temperature was held at 60 °C for 1 minute, then increased to 180 °C at the rate of 5 °C/min,
and ramped to 250 °C at the rate of 20 "C/min, and held at the final temperature for 5 minutes.
RESULTS
Gas chromatography and detection
All the target compounds were well separated by the selected column and temperature program
(Figure 3). One derivative compound was formed for symmetrical formaldehyde, acetone, and
TFB, and two geometrical isomers of the derivatives were formed for the rest of Ae compounds.
Good detector response linearity was obtained for carbonyl-PFBHA derivatives generated from
the reaction in both water and methanol and analyzed by a GC-ECD. The correlation coefficient
(R2) was larger than 0.99 over the calibration range of 0.04 - 2.5 ng/mL for all of the compounds
tested. The precision of the instrument was tested by injecting the same concentrated carbonyl-
PFBHA standard over a two-weeks period. The response was reproducible and the retention
time did not change significantly within two weeks (± 0.1 min). The relative standard deviation
of response was less than 10% for the target compounds during the two weeks (with 7 replication
injections). The analytical detection limit was about 10 pg for the carbonyl-PFBHA derivatives.
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The detection limit is equivalent to -10 ng/L of caibonyl compounds in a 20-L sample collected
from stationary source emissions.
Derivatization yields of carbonyls with PFBHA In water, In methanol, and in a cet on it rile
The derivatization yield of caibonyl with PFBHA in different solvents was studied. Samples
with the same concentrations of carbonyls and PFBHA were prepared in water, methanol, and
acetonitrile. These samples were allowed to react for 10,20,30,60, and 90 minutes, and 2,4,8,
16,20, and 24 hours. Duplicate samples were prepared for each time period. Samples were
extracted with 2 mL of hexane containing 1,2-dibromopropane after the designated reaction time,
and extracts were analyzed by a GC-ECD.
Aldehydes seemed to react faster than the ketones with PFBHA in each of the three solvents.
The reactions of aldehydes with PFBHA were more than 90% completed after 2 hours, but the
reactions of ketones with PFBHA required more than 8 hours for completion. The aldehyde-
PFBHA derivatives were stable in both methanol and acetonitrile; however, they gradually
dissociated in water after they formed (Figures 4a to 4c). Higher derivatization yields were
obtained for the ketones in both methanol and acetonitrile than in water. Thus, a better
sensitivity was obtained using methanol or acetonitrile as the solvent rather than using water as
the solvent. For the subsequent tests, methanol was chosen as the solvent due to the toxicities of
acetonitrile.
Stabilities of carbonyls dissolved In water and In methanol
A two-week stability study was conducted for aldehydes and ketones in both water and
methanol. Known amounts of carbonyls were spiked in both solvents. Phenol is often present in
some industrial emissions that contain carbonyl compounds; therefore, the effect of phenol on the
stability of carbonyls was also tested. Caibonyl mixtures plus phenol were prepared in water and
methanol, and carbonyls were also added into a condensate field sample that contained phenol.
The field sample was collected during an unrelated field test at a wood products plant press and
dryer, and was obtained from the Paper Industry's National Council for Air and Stream
Improvement (NCASI). The stability of carbonyls in water and in methanol with the addition of
PFBHA was tested as well. Samples with addition of PFBHA were split into two sets. One set
was stored in a refrigerator, and another set was stored at room temperature.
An aliquot was removed from each sample prepared above at designated storage times (0,1,2,5,
7,10,14 days). Samples containing carbonyls only were allowed to react with PFBHA for 24
hours and then extracted with hexane containing 1,2-dibromopropane. Samples containing
carbonyls and PFBHA were extracted directly with hexane containing 1,2-dibromopropane. The
sample extracts were analyzed by a GC-ECD, and the response of each compound was compared
with the data from Day 0. Hie results of the caibonyl stability studies are listed in Table 1.
All the compounds tested except acrolein were stable over the testing period in both water and
methanol. Degradation of acrolein was observed in both solvents. In the presence of phenol
(—25 gg/mL), formaldehyde, acetaldehyde, and hexaldehyde decayed slowly in water, but not in
methanol. The effect of phenol on acrolein degradation was further tested by preparing acrolein
solutions (15 ng/mL) with different phenol concentrations (5 - 50 |ig/mL) in both water and
methanol. In water, the acrolein decay rate increased along with the increase of phenol
concentration, but the decay rate observed for acrolein in methanol appeared to be the same
regardless of the phenol concentrations. In both solvents, the phenol concentration did not
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decrease over time. The results show that phenol probably promoted the dimerization of acrolein
in water/ but this effect was not significant in methanol.
The addition of PFBHA stabilized carbonyls in both solvents. In methanol, carbonyl-PFBHA
derivatives were stable over the testing period stored at room temperature and in the refrigerator.
In water, formaldehyde, acetaldehyde, acrolein, and hexaldehyde were stabilized by PFBHA;
however, as observed in the derivatization yield study, the derivatives of acrolein, hexaldehyde,
and MIBK gradually dissociated in water stored either at room temperature or in the refrigerator.
These results suggest that methanol is a better preservative for carbonyl compounds. In addition,
carbonyl-PFBHA derivatives in hexane stored in a refrigerator were stable for 7 days but then
started to decay. This was probably due to the dissociation of PFBHA derivatives in hexane.
Comparison of the Retention and Recovery Efficiencies of Carbonyl Compounds Collected
in Water and in Methanol
The retention and recovery efficiencies for the selected compounds were tested using midget
impingers filled with 20 mL of methanol or water. The retention in the upstream impinger was
> 85% for all the compounds tested when collected in methanol, but the retention was < 70% for
acetaldehyde and < 60% for acrolein, butyraldehyde, and hexaldehyde when collected in water
(Table 2). The recovery efficiency (total mass collected in upstream and downstream impingers)
was > 80% for all the compounds tested using methanol as the collection solvent. When water
was used as the solvent, the recovery efficiency was > 80% for acrolein, MEK, and MIBK but
< 75% for butyraldehyde and hexaldehyde (Table 3). Also, larger variabilities of retention and
recovery efficiencies were observed when water was used as the collection solvent versus using
methanol as the collection solvent. When tested under the humid condition (-10% water v/v),
the presence of moisture appeared to have no effects on the retention and recovery efficiencies
for carbonyl compounds.
The retention and recovery efficiencies of carbonyls were also tested using water with the
addition of PFBHA as the collection solvent. The retention in the first impinger was slightly
higher for acrolein and hexaldehyde, but the recovery efficiency of hexaldehyde was still less
than 75%.
CONCLUSIONS AND RECOMMENDATIONS
A test method has been developed in the laboratory for the collection and measurement of
carbonyls from stationary source emissions. Carbonyls are more stable in methanol than in
water, and higher retention and recovery efficiencies for carbonyls were obtained using methanol
as the collection solvent. The derivatization yield of carbonyl-PFBHA was higher in methanol
than in water, thus, a better sensitivity was obtained using methanol as the solvent. The
preliminary laboratory evaluation indicates that this method can be applied to the collection and
analysis of carbonyls, especially unstable carbonyl compounds such as acrolein, in stationary
source emissions; however, field tests are needed to further test and evaluate this method.
DISCLAIMER
The research described in this paper has been funded wholly or in part by the United States
Environmental Protection Agency through Cooperative Agreement No. CR 823866-01 to
Research Triangle Institute, Research Triangle Park, NC. It has been reviewed by the Agency
and approved for publication. Approval does not signify that the contents necessarily reflect the
4

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view and policies of the Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
REFERENCES
1.	Carlier P., Hannachi H., Mouvier G. Atmos. Environ. 1986,20,2079-2099.
2.	Grosjean D. Environ. Sci. Technol. 1982,16,254-262.
3.	Johnson L., Josefsson B., Marstoip P. Int. J. Environ. Sci. Technol 1989,23,556-561.
4.	Koshy K.T., Kaiser D.G., VanDerSlik AX. J. Chrom. Sci. 1975,13,97-104.
5.	Glaze W.H., Koga M., Cancilla D, 1989, Environ. Sci. Technol. 23,838-847.
6.	Yu J., Jeffries H.E., Le Lacheur R.M. 1995, Environ. Sci. Technol. 29,1923-1932.
7.	Ghilarducci, D.P. and Tjeerdema, R.S. Rev. of Environ. Contamination and Toxicology 1995,
144,96-146.
5

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Table 1. Comparison of stability of carbonyls in water and in methanol after two weeks.
Relative Response % (Day 14/Day 0)'
Formaldehyde Acetaldehyde Acrolein Acetone MEK Butyraldehyde M1BK Hexaldehyde
Water (4°C)
93.2
93.5
67.4
102.2
107.1
NAa
94.5
84.2
Waterfphenol (4°C)
81.3
84.5
47.6
91.3
90.2
NA2
82.2
70.1
Field water sample (4°C)
(Containing phenol)
92.1
78.2
65.3
92.3
95.1
NA1
97.5
NA1
Water+phenol+PFBHA (4eC)
107.2
103.2
86.2
117.1
115.1
NA1
87.5
83.5
Water+phenol+PFBHA (R.T.1)
95.2
97.5
72.7
116.1
115.1
HA2
86.5
80.5
Methanol (4°C)
99.2
95.3
46.8
95.2
105.1
116.1
95.3
97.2
Methanol+phenol (4aC)
98.3
95.2
53.5
88.9
85.6
107.7
87.2
91.5
Methanol+phenol+PFBHA (4°C)
93.0
94.1
97.8
96.9
101.1
106.6
113.1
91.8
Methanol+phenol+PFBHA (R.T.J)
105.9
92.6
96.0
93.7
97.5
105.7
115.3
90.7
Carbonyls-PFBHA-Hexane4
111.3
NA2
116.2
114.5
115.4
H8.5
119.2
116.8
'The stability of carbonyls was represented as the response from each day over the response from Day 0 (average of two replicate
samples). ~
2Not tested.
'Room temperature.
4These values are the relative response after one week.
On

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Table 2. Retention (A) and recovery efficiencies (B) of cart>onyls using water or
methanol as the collection solvent under dry condition.
Methanol	Water
A.
Retention
Precision
%RSD
Retention
Precision
%RSD
Formaldehyde
95.7%
0.8%
93.8%
0.4%
Acetaldehyde
92.8%
5.6%
70.8%
12.0%
Acetone
92.3%
3.2%
85.4%
4.9%
Acrolein
85.7%
2.7%
59.6%
13.4% .
MEK
94.8%
2.0%
84.4%
2.9%
Butyraldehyde
94.8%
1.0%
58.4%
4.2%
MIBK
98.2%
0.7%
82.5%
4.0%
Hexaldehyde
97.7%
0.4%
57.8%
15.7%
B.
Recovery
Efficiency
Precision
%RSD
Recovery
Efficiency
Precision
%RSD
Fonnaldehyde
85.8%
3.6%
88.6%
7.5%
Acetaldehyde
89.1%
5.9%
100.7%
14.3%
Acetone
97.3%
13.1%
112.2%
12.1%
Acrolein
94.5%
8.2%
96.0%
6.9%
MEK
107.3%
6.8%
110.9%
10.9%
Butyraldehyde
87.8%
2.2%
75.0%
2.7%
MIBK
115.0%
9.3%
76.6%
13.2%
Hexaldehyde
83.1%
3.1%
60.5%
16.4%

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Table 3. Retention (A) and recovery efficiencies (B) of carbonyls using water or
methanol as the collection solvent under humid condition (10% water v/v).

Methanol
Water


Precision
Retention
Precision
A.
Retention
%RSD
%RSD
Formaldehyde
90.7%
0.3%
95.3%
0.9%
Acetaldehyde
94.8%
0.6%
70.0%
12.3%
Acetone
99.2%
0.5%
86.2%
1.6%
Acrolein
86.2%
0.8%
54.6%
5.3%
MEK
95.0%
0.5%
83.7%
4.7%
Butyraldehyde
93.7%
0.3% .
62.9%
16.4%
MIBK
98.7%
0.1%
85.9%
7.0%
Hexaldehvde
92.5%
1.7%
41.3%
5.9%

Recovery
Precision
Recovery
Precision
B.
Efficiency
%RSD
Efficiency
%RSD
Formaldehyde
91.6%
4.5%
95.6%
2.1%
Acetaldehyde
97.9%
0.9%
87.8%
4.7%
Acetone
110.7%
5.4%
108.5%
2.4%
Acrolein
105.8%
3.6%
113.1%
6.1%
MEK
111.6%
6.8%
108.7%
4.7%
Butyraldehyde
90.4%
3.0%
76.5%
5.2%
MIBK
101.9%
10.2%
80.1%
3.7%
Hexaldehyde
87.0%
2.0%
68.6%
7.1%

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Figure 1, Dynamic dilution system
nitrogen
heated
transfer
line
humidifier
t
heated zone
dilution system
formaldehyde,
acetaldehyde,
acetone, acrolein,
butyraldehyde,
hexaldehyde,
methyl ethyl ketone, and
methyl isobutyl ketone
in nitrogen
sampling
ports

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Figure 2. Sampling train for carbonyl compounds
heated Teflon	¦" bal1 ioin,s held
sampling tube	with pinch clamps
L" connector
\ /IV
U" connector
drierite
L" connector
ice
bath
Sampling
Pump
impingers
(methanol-filled
or
Water-filled)

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Figure 3. Gas chromatogram of carbonyt compounds as their pentafluorophenylhydrazones (-0.4 ppm).
3.0E4 n
2.5E4 «
O
2.0E4 •
1.5E4 ¦
1.0E4 *
5000
0
10
20
30
Time (ntin)

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Figure 4. Carbonyl-PFBHA derivatization yields in water, in methanol, and in acetonitrile
WATER
10
16
«
« I?
e
o
a
a e
0
>
0


10
15	20
METHANOL
15
20
25
25
ACETONITRILE
5	10	15	20
Reaction Time (hours)
25
—~-HCHO —•—ACETONE -A—ACROLEIN -*~MEK
12

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TECHNICAL REPORT DATA
1. REPORT NO.
EPA6Q0/A-98-049
2.

i. TITLE AND SUBTITLE
Measurement of carbonyl compounds from stationary
source emissions using a PFBHA-GC/ECD method
5.REPORT DATE
March 18, 1998
6.PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Z. Fan, et.al., Research Triangle Institute,
Research Triangle Park, NC and Frank Wilshire,
USEPA/ORD/HEASD, Research Triangle Park, NC 27711
8.PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute, P.O. Box 12194,
Research Triangle Park, NC 27709
10.PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
COOP CR823866
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. Environmental Protection Agency
Office of Research and Development
NERL-RTP/HEASD/EMMB
Research Triangle Park, NC 27711
13.TYPE OF REPORT AND PERIOD COVERED
Meeting presentation
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
To be presented at the 91st annual AWMA Meeting, June 14-19, 1998 in San Diego, CA
16. ABSTRACT
Carbonyl compounds have received increasing attention because of their important
role in ground-level ozone formation. Currently, there is no validated stationary
source method for the measurement of multiple carbonyl compounds containing unstable
compounds such as acrolein. This paper presents the results for the laboratory
development of a source method for the collection and analysis of eight carbonyl
compounds (acetone, acrolein, acetaldehyde, butyraldehyde, formaldehyde,
hexaldehyde, methyl ethyl ketone, and methyl isobutyl ketone).
Samples are collected in two midget impingers, each containing 20 ml of methanol.
The suggested sampling period is for 20 minutes and the sample rate is one liter per
minute, resulting in a total collected sample of 20 liters. A two to five ml sample
aliquot is removed, following completion of the sampling period, and stabilized with
0-2,3,4,5,6 -pentafluorobenzyl hydroxylamine hydrochloride (PFBHA) . The sample is
reacted for a period of time, extracted with hexane and then analyzed by GC/ECD.
The method is resistant to degradation of carbonyls from interference by phenols,
has a detector response of R22 0.99 over the range of 0.04-2.5 ptg/ml, and has an
analytical detection limit of ~ 10 picograms. For a 20 minute field sample, this
would equate to a source method detection limit of - 10 ng/ml.
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