EPA/600/A-94/045
Field Comparison of Portable Gas Chromatographs with Method TO-14
Richard E. Berkley and Maribel Colon
US Environmental Protection Agency, Research Triangle Park, NC 27711
Jesus Gonzalez and Israel Droz
University of Puerto Rico School of Public Health, San Juan, PR 00936
Jeffrey Adams, Christopher Fortune, and Karen Oliver
ManTech Environmental Services, Research Triangle Park, NC 27709
Daniel R. Coleman, CMS Research Corporation, Birmingham, AL 35244
Clayton Wood, HNU Systems, Incorporated, Newton, MA 02161
-------
Field Comparison of Portable Gas Chromatographs with Method TO-14
Richard E. Berkley and Maribel Colon
US Environmental Protection Agency, Research Triangle Park, NC 27711
Jesus Gonzalez and Israel Droz
University of Puerto Rico School of Public Health, San Juan, PR 00936
Jeffrey Adams, Christopher Fortune, and Karen Oliver
ManTech Environmental Services, Research Triangle Park, NC 27709
Daniel R. Coleman
CMS Research Corporation, Birmingham, AL 35244
Clayton Wood
HNU Systems, Incorporated, Newton, MA 02161
ABSTRACT
A field-deployable prototype fast gas chromatograph (FGC) and two
commercially-available portable gas chromatographs (PGC) were evaluated by measuring organic
vapors in ambient air at a field monitoring site in metropolitan San Juan, Puerto Rico. The data
were compared with simultaneous grab samples which were collected in six-liter
Summa-polishedฎ canisters and analyzed by method TO-14. Because of fluctuating retention
times, the FGC produced no useable data. High humidity levels may have adversely affected its
performance. Both commercially-available PGCs performed successfully, and data from twenty
analyses were compared with the reference method.
This paper has been reviewed in accordance with US Environmental Protection Agency's
peer and administrative review policies and approved for presentation and publication. Mention
of trade names or commercial products does not constitute endorsement or recommendation for
use.
INTRODUCTION
During June 1993 a field study, organized under auspices of US Environmental Protection
-------
Agency, Atmospheric Research and Exposure Assessment Laboratory, Research Triangle Park,
NC, was conducted near San Juan, Puerto Rico to compare data produced by three gas
chromatographs with reference data from samples which were collected simultaneously in six-liter
Summa-polishedฎ canisters and subjected to laboratory analysis by Method TO-14 [1]. The
purpose of this study was to assess the performance of the field-deployable chromatographs.
They were (1) a prototype high-speed (fast) chromatograph (FGC) developed by Professor
Steven Levine at the University of Michigan School of Public Health in cooperation with HNU
Systems under Environmental Protection Agency Cooperative Agreement No. CR 817123 with
the University of Michigan, (2) the CMS MINICAMSฎ, and (3) the HNU Model 311ฎ. Field-
deployable (portable) gas chromatographs (PGC) offer the advantages that they produce data
immediately, and they can produce more data at lower cost than laboratory-based methods. In
addition, samples analyzed on-site do not undergo lengthy storage pending analysis, as samples
analyzed by laboratory-based methods usually must.
There are some disadvantages to use of PGCs, the principal one being generally lower
quality performance. PGCs often incorporate less-sophisticated components than are used in
laboratory instruments in order to reduce cost and size. Many operate isothermally, and most use
short columns to decrease analysis times, so they are not able to analyze as many compounds per
run as laboratory instruments. PGCs can be difficult to operate properly because of inferior
components and because they experience ambient temperature fluctuations and other
consequences of deficient shelter which are not normally encountered by laboratory instruments.
In previous field studies of this kind, EPA purchased PGCs and evaluated them, or
employed a contractor to do so [2-6]. More recently, an EPA contractor borrowed several
instruments and evaluated them together during a field study [7]. In the multi-instrument field
-------
study, it was noticed that the number of PGCs which can be evaluated is limited by the number of
competent operators available, which is limited in turn by available space inside shelter at the
sampling site. The predicament of an operator can become intolerable when confronted by
several different instruments of variable and unknown temperament, functioning under the adverse
conditions typical of a field study and without immediate access to technical support. In fact,
extensive direct assistance by factory technical representatives proved crucial to success when
several different PGCs were evaluated simultaneously. Operators were overworked, and it was
apparent that one technically-trained person is needed for each kind of instrument. In this study,
each instrument was operated by a factory representative.
EXPERIMENTAL
The rationale for the study was direct comparison of data produced by different methods,
using TO-14 analysis of canister grab samples as the reference method. Periodically, all
instruments collected samples simultaneously through collocated inlets as a canister was filled
nearby (within 20 cm). Ambient concentrations were lower than expected. In order to obtain
some data at higher concentrations, samples were collected inside a mobile laboratory, where
concentrations were higher than outside. Because of this, and because site selection was
constrained by requirements for shelter and line power, the data are not necessarily representative
of conditions in Catano. The purpose of this study was to evaluate the instruments under field
conditions, not the air in Catano.
Site Selection
Site selection was determined primarily by the current location of the least-transportable
participating instrument; the FGC was located at the University of Puerto Rico School of Public
Health. Secondary consideration in site selection was given to using a site where there was
-------
perception of an air pollution problem. The most convenient and practical of several sites
considered was a monitoring station operated by the Junta de Calidad Ambiental (Environmental
Quality Board) at the jail in Bayamon, which was within the San Juan Metropolitan Area and
generally downwind of the Catano industrial area. JCA had two small shelters on site with air
conditioning and electric power. The PGC operators collaborated to rent a large recreational
vehicle to which electric power from a JCA building was connected so it could be used as a
mobile laboratory during the study. A schematic (not to scale) of the area around the site is
shown in Figure 1.
Audit Standard
Occasionally, each instrument analyzed an audit standard which had been prepared in the
EPA/AREAL laboratory in Research Triangle Park, North Carolina. The audit standard was
certified before the study by analysis with a gas chromatograph equipped with dual flame
ionization and electron capture detectors (GC/FID+ECD). After the study it was analyzed again
by a gas chromatograph with a mass selective detector (GC/MSD). Results of these analyses are
compared in Figures 2 and 3, which include all 41 compounds on the TO-14 target list. There
was little change in the audit standard between the two analyses. Canister samples of ambient air
collected during the study were analyzed by GC/MSD.
Canister Sampling
Canisters were filled by holding the valve within 20 cm of the group of PGC inlets and
opening it just far enough to fill the canister while the PGCs were sampling. This procedure could
not ensure that all methods analyzed exactly the same air, but it should produce quite similar
results during calm weather if air is well-mixed with vapors from remote sources.
High-Speed Chromatograph
-------
The prototype FGC was developed by Levine. Details of its unique features have been
presented elsewhere [8-12]. A small volume of air was isolated in a sample loop, then passed
through a Monelฎ capillary cooled to -120ฐC by vapor which was boiled out of a reservoir of
liquid nitrogen at a controlled rate. Sample loops with volumes from 0.25 to 5 ml could be used.
After the air sample was flushed into the Monel capillary by a helium stream, the capillary was
placed in line with the column by operating a multi-port valve, and the Monel capillary was
rapidly heated by capacitive discharge. The 0.25 mm id column was operated isothermally
between 40-200ฐC. Carrier flow velocity was within the range of 60 to 175 cm/sec. The injection
bandwidth was 10 msec. Dual ECD and 10.2 eV PID used an electrometer which was specially
designed to cope with extremely narrow peaks. During preliminary laboratory evaluation with a
flame ionization detector (FID), which has essentially no volume, analyses were completed in less
than 30 s, and excellent separation was demonstrated. Detection limits for TO-14 target list
compounds varied between 1-300 ppb, depending on the sensitivity of the FID to the individual
compound [10]. Using an ECD, separation was slightly less, and it took nearly one minute to
complete a chromatogram, but detection limits for highly halogenated compounds appeared to be
below one ppb [13]. During the present study, the length of the 0.25 mm id column was
increased from 10 m to 30 m in an attempt to elute benzene after the initial baseline excursion.
Commercially-Available Portable Gas Chromatographs
Two commercially-available portable gas chromatographs were evaluated in the study,
each operated by a factory representative. Operators were responsible for calibration,
maintenance, and troubleshooting their own equipment.
CMS Minicams The Series 2000 Field MINICAMS was a field-deployable gas
chromatograph which operated on 110 V AC line power. It measured 25.4 X 30.5 X 21.6 cm,
-------
weighed 8.6 kg, and had an on-board microcomputer which used a custom software package to
control operation and communicate data to an external computer. The unit used in this study was
equipped with a FED and a solid sorbent preconcentrator. Samples were collected on a
proprietary carbon-based sorbent bed from an air stream which was drawn through it at 200
ml/min for 260 s. The sample was injected by operating a 3-way valve to place the sorbent bed in
the carrier stream flowing in the opposite direction to the sample stream. Then it was rapidly
heated to 350ฐC for 40 s. The 15 m X 0.32 mm fused silica column was coated with 5 ^m DB-1.
During analysis, column temperature was increased ballistically from 40ฐ to 180ฐC at a rate of
329ฐC/min.
HNU Model 311. The HNU 311 is a field-deployable gas chromatograph which operates
on 110 V AC line power. It measures 38.1 X 56.4 X 24.6 cm and weighs 30 kg. An on-board
microprocessor can deliver data directly to an on-board printer or pass it to an external computer
for processing or storage on disk. The unit used in this study was equipped with both ECD and
PID, but the compounds for which it was calibrated were detected by PID. A continuously-
pumped air stream was sampled periodically for 20 s by diverting the contents of a sample loop
with a multi-port valve. The 25 m X 0.53 mm fused silica column was coated with 1.0 ^m of
NB-30. Nitrogen carrier flow rate was 15 mL/min and column temperature was 80ฐC.
RESULTS AND DISCUSSION
The study was carried out during June 22-25, 1993. The first day was entirely spent in
setting up equipment, connecting utility supplies, and startup. Routine periodic autosampling by
the two PGCs began on June 23 and continued until the study ended on June 25. Periodic
manually-initiated sampling by the FGC was done during daylight hours.
High-Speed Gas Chromatograph
-------
The FGC was plagued by significant shifts in retention times throughout the study, and its
sensitivity was diminished. This problem may have resulted from water in the samples, since
relative humidity was much greater than had been encountered during laboratory evaluation.
Ambient temperature at this field site was about 35ฐC and relative humidity was near 100%.
Another possibility is that some instrument failure may have led to part or all of the problem. The
cause is under investigation. If necessary, moisture could be removed from samples before
analyzing them by this method. No useful data were produced by the FGC during this study.
Portable Gas Chromatographs
Both PGCs required several hours for setup, warm-up, and tune-up. Once operational,
both performed effectively for the duration of the study.
Data from Audit Standard Analyses. Each PGC performed several analyses of the
audit standard mixture of Method TO-14 target list compounds. Data from several analyses of
the audit standard by the CMS MINICAMS are shown in Figure 4, and HNU 311 audit data are
shown in Figure 5. MINICAMS results for o-xylene were high. Otherwise, field audit data are in
good agreement with laboratory analyses for both PGCs.
Comparison of PGC and TO-14 Data. Canister samples were analyzed for all 41
compounds on the TO-14 target list, while the PGCs were calibrated only for benzene, toluene,
m,p-xylene, and o-xylene. Table 1 shows data from simultaneous canister and PGC sampling of
outdoor air, and Table 2 shows similar data for air sampled inside the mobile laboratory. Indoor
air samples were taken because outdoor analyte levels were lower than expected, as seen
throughout Table 1. Because of its fuel tank, engine, generator, refrigeration equipment,
upholstery, and limited ventilation, air inside the mobile laboratory contained much higher levels
of TO-14 target compounds. Inspection of the data in Tables 1 and 2 shows that agreement
-------
between methods, though not exact, was close.
An understanding of how well the methods agree can be obtained by taking the average of
the absolute values of the differences between PGC and TO-14 results for each compound for all
comparison runs. Average absolute differences are represented as red horizontal lines in Figure 6.
The standard deviation of the absolute values of the differences is shown by the length of the bar
above and below the red line. This figure shows that the differences are finite, real, and relatively
small, except at the lowest concentrations. The averages are not much larger than their standard
deviations, which suggests that the differences are essentially random and do not contain a large
component of systematic error. Averaging the differences without taking absolute values, so that
positive and negative values tend to cancel each other, produces the results shown in Figure 7. A
negative bias of insignificant magnitude is apparent.
Retention times are contrasted with standard deviations of retention times in Figure 8.
The width of the red boxes at the ends of the bars represents standard deviation, which was small
enough to suggest that chromatographic conditions were stable during the study, and that the
peak identification algorithms were finding no more than one actual compound for each analyte.
CONCLUSIONS
The causes of the retention time instability and loss of sensitivity experienced by the Fligh-
Speed Gas Chromatograph remain to be determined. If high moisture levels were responsible,
then a dry purge preconcentrator injection system will be incorporated. Other indicated repairs or
modifications will also be done, after which the FGC will be re-evaluated at a field study in some
hot and humid environment. Both PGCs performed as claimed by their manufacturers and are
clearly suitable for use as field deployable instruments for analyzing volatile organic compounds in
ambient air, provided that adequate shelter and utility support are available.
-------
REFERENCES
1. Compendium of Methods Tor the Determination or Toxic Organic Compounds in
Ambient Air. Environmental Protection Agency, Atmospheric Research and Exposure
Assessment Laboratory, Research Triangle Park, NC 27711. EPA-600/4-84-017. June 1988.
2. Richard E. Berkley, Jerry L. Yarns, William A. McClenny, James Fulcher. "Field Evaluation
of Photovac 10S70 Portable Gas Chromatograph." Proc. 1989 EPA/AWMA International
symposium on Measurement of Toxic and Related Air Pollutants, AWMA, Pittsburgh, PA, 1989,
pp. 19-26.
3. Richard E. Berkley, Karen D. Oliver, Keith Kronmiller. "Performance Optimization of
Photovac 10S70 Portable Gas Chromatograph." Proc. 1990 EPA/AWMA International
Symposium on Measurement of Toxic and Related Air Pollutants, AWMA, Pittsburgh, PA, 1990,
pp 849-854.
4. Richard E. Berkley. "Evaluation of Emission Sources and Hazardous Waste Sites Using
Portable Chromatographs." Proc. Second International Symposium on Field Screening
Methods for Hazardous Wastes and Toxic Chemicals, ICAIR Life Systems, Inc., Cleveland, OH,
1991, Paper 003.
5. Jerry L. Yarns, R. E. Berkley. "Measurement of Volatile Organic Compounds in Two
Autoex-Soviet Field Studies Using Portable Gas Chromatography." Proc. 1991
EPA/AWMA International symposium on Measurement of Toxic and Related Air Pollutants,
AWMA, Pittsburgh, PA, 1991.
6. Richard E. Berkley, Jerry L. Yarns, Joachim Pleil. "Comparison of Portable Gas
Chromatographs and Passivated Canisters for Field Sampling Airborne Toxic Organic
Vapors in the United States and the USSR." Environ. Sci. Technol., Vol. 25, No. 8, 1991,
1439.
7. R. E. Berkley, M. Miller, J. C. Chang, K. Oliver, C. Fortune. "Evaluation of
Commercially-Available Portable Gas Chromatographs." Proc. 1992 EPA/AWMA
International symposium on Measurement of Toxic and Related Air Pollutants, AWMA,
Pittsburgh, PA, 1992, pp 413-418.
8. Robert F. Mouradian, Steven P. Levine, Richard D. Sacks. "Evaluation of a Nitrogen-
Cooled, Electrically-Heated Cold Trap Inlet for High-Speed Gas Chromatography." J.
Chrom. Sci. 28, 1990, 643.
9. S. P. Levine, H. Q. Ke, R. F. Mouradian, R. Berkley, J. Marshall. "High Speed
Chromatography for Air Monitoring." Proc. Second International Symposium on Field
Screening Methods for Hazardous Wastes and Toxic Chemicals, ICAIR Life Systems, Inc.,
Cleveland, OH, 1991, Paper 007.
-------
10. Huiqiong Ke, Steven P. Levine, Robert F. Mouradian, Richard E. Berkley. "High Speed
Chromatography for Air Monitoring." Proc. 1991 EPA/AWMA International symposium on
Measurement of Toxic and Related Air Pollutants, AWMA, Pittsburgh, PA, 1991.
11. H. Q. Ke, S. P. Levine, R. F. Mouradian, R. E. Berkley. "Fast Gas Chromatography for
Air Monitoring: Limits of Detection and Quantitation". Amer. Ind. Hyg. Assoc. J., 53,
1992, 130.
12. H. Q. Ke, S. P. Levine, R. Berkley. "Analysis of Complex Mixtures of Vapors in Air by
Fast-Gas Chromatography." Air Waste Manag Assoc. J., 42, 1992, 1446.
13. H. Q. Ke, R. E. Berkley. Unpublished data.
-------
Table 1. Canister Grab Sample and Portable Gas Chromatograph Data ฃrom Outdoor Air at Bayamon C^rcel
1,1,1-Tri-
Dichloro- chloro-
me thane ethane
June 23, 1993
12:23
TO-14 0.26
CMS
HNU
12:46
TO-14 0.80
CMS
HNU
13:00
TO-14 ND
CHS
HNU
13:23
TO-14 0.24
CMS
HNU
June 24, 1993
10:23
TO-14 ND
CMS
HNU
11:26
TO-14 0.24
TO-14 0.00
CMS
HNU
11:39
TO-14 ND
CMS
HNU
11:53
TO-14 4.95
CMS
HNU
12:08
TO-14 4.08
CMS
HNU
June 24, 1993
12:21
TO-14 7.67
CMS
HNU
12:28
TO-14 0.26
CMS
HNU
15:23
TO-14 0.88
CMS
HNU
June 25, 1993
09:24
TO-14 0.82
CMS
HNU
09:31
TO-14 0.61
CMS
HNU
09:58
TO-14 1.03
CMS
HNU
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
0.45
0.00
0.00
ND
ND
0.23
0.00
0.00
0.27
0.00
0.00
ND
Ethyl -
Benzene Toluene benzene
0.
0.
0.
1.
0.
0.
0.
0.
0.
0,
0,
0.
2.
2.
0
2
2
4
0
2
2
0
0
4
0
2
1
0
2
3
0
1
2
0
0
1
0
1
0
0
0
2
0
1
2
0
91
40
00
,77
80
00
.65
.60
.00
,77
,00
.00
.05
.20
,00
.57
.42
.10
.00
.00
.20
.00
.73
.00
.00
.14
.50
.00
.29
.30
.00
.54
.70
.00
.73
.30
.00
.15
.00
.00
.88
.20
.00
.09
.80
.00
2
6
3
5
5
10
1
2
2
5
a
10
15
20
12
7
8
10
12
6
5
7
0
a
5
4
2
a
5
7
6
4
5
3
2
1
0
2
4
0
2
4
0
1
3
0
.20
.50
.20
.38
.00
.30
.37
.00
.20
.38
.80
.70
.79
.10
.80
.95
.38
.60
.20
.82
.40
.10
.44
.30
.90
.75
.90
.10
.54
.00
.30
.50
.70
.90
.23
.90
.00
.50
.70
.00
.57
.20
.00
.95
.20
.00
0.
0.
0
0
0
0
0
0
0
0
ND
39
(TO
ND
.64
.93
.00
.49
ND
.30
.18
.13
ND
.19
.19
ND
1,3,5- 1,2,4-
m,p- 4-Ethyl- Trimethyl Trimethyl
Xylene o-Xylene toluene benzene benzene
0.00
1.10
0.00
1.51
2.40
1.40
0.00
0.70
0.30
0.00
0.00
0.00
2.23
3.60
1.10
3.18
3.05
0.00
3.00
1.74
2.00
1.80
0.00
2.60
0.90
1.02
0.90
1.50
1.58
2.10
1.10
1.07
1.70
0.00
0.14
0.70
0.00
0.84
0.00
0.00
0.50
0.00
0.50
0.56
1.70
0.00
0.
3.
0.
0,
0.
1,
0.
0.
2
0,
0,
1,
0,
2 ,
2 .
0
0
4
2
0
0.
3
0
1
2
0
0
0
0
0
2
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
24
00
80
,65
.90
,90
.00
.00
.70
.00
.00
.20
.83
,00
,60
.73
.78
.10
.90
.58
.80
.10
.00
.00
.70
.39
.50
.00
.69
.90
.70
.33
.90
.89
.11
.70
.00
.37
.00
.00
.25
.00
.00
.00
.70
.00
ND ND 0.11
0.00
0.00
0.16 ND 0.54
0.00
0.00
ND ND ND
ND ND ND
0.58 0.45 1.78
0.26 0.24 0.73
0.00 0.00 0.00
0.37 0.13 0.82
ND ND ND
ND ND 0.54
0.26 0.11 0.45
0.36 0.09 0.69
ND ND 0.20
ND ND 0.37
ND ND 0.36
0.09 ND 0.28
0.00
0.00
-------
Table 2. Canister Grab Sample and Portable Gas Chromatograph Data from Air Inside Temporary Mobile Laboratory
June
15:36
TO-14
CMS
HNU
June
15:44
TO-14
TO-14
CMS
HNU
15:56
TO-14
CMS
HNU
June
09:38
TO-14
CMS
HNU
09:44
TO-14
CMS
HNU
1,1,1-Tri-
Dichloro- chloro-
Freon 11 methane ethane
23, 1993
0.93 19.67 1.74
24, 1993
(Replicate)
0.95 16.68 1.36
1.14 17.01 1.36
1.32 20.44 1.88
25, 1993
0.80 14.26 1.14
1.26 15.96 1.24
Benzene
3.
0.
6.
5.
6.
9.
6.
7.
10.
8.
5.
9.
4.
6.
11.
3.
92
50
40
79
01
10
90
38
10
30
63
40
30
33
60
60
Toluene
12
15
22
14
14
16
21
16
17
23
15
17
13
16
19
14
.70
.80
.80
.61
.30
.60
.90
.07
.20
.00
.28
.50
.90
.20
.50
.70
Ethyl- m,p-
benzene Xylene Styrene
0.53 2
4
4
0.70 3
0.59 2
4
2
0.71 3
4
3
0.93 3
0
0
0.98 3
5
1
.23 1.89
.40
.70
.28 1.78
.99 1.30
.30
.80
.74 2.28
.30
.30
.54 1.20
.00
.60
.55 1.67
.00
.60
1,3.5-
4-Ethyl- Trimethyl
o-Xylene toluene benzene
1
4
4
1
1
4
4
1
5
3
1
3
2
2
4
0
.89 0.32 0.13
.10
.90
.83 0.22 0.26
.72 0.12 0.21
.80
.50
.99 0.21 0.27
.30
.30
.62 0.25 0.27
.60
.10
.01 0.26 0.24
.20
.00
1,2,4-
Trimethyl-
benzene
1.08
1.06
1.01
1.17
1.39
1.11
-------
Table 3. Summary of Differences Between TO-14 Data
and Portable Gas Chromatograph Data
Benzene
CMS Minicams
Maximum Absolute Difference
Mean Absolute Difference
Minimum Absolute Difference
Std Dev of Abs Difference
Bias (Mean Difference)
HNU Model 311
Maximum Absolute Difference
Mean Absolute Difference
Minimum Absolute Difference
Std Dev of Abs Difference
Bias (Mean Difference)
5
1
0
1
-0
5
1
0
1
1
.27
.67
.05
.41
.92
.27
.56
.03
.06
.09
Toluene m,p-Xylene
7
2
0
1
-1
10
3
0
2
-1
.86
.33
.33
.70
.93
.10
.69
.28
.66
.80
3.
1.
0.
0.
-0.
2.
0.
0.
0.
0.
54
16
00
95
35
94
69
00
78
20
o-Xylene
3.
1.
0.
1.
-1.
3.
1.
0.
1.
-1.
34
21
00
16
15
43
48
00
02
24
-------
LEGENDS FOR FIGURES
Figure 1. Schematic of the field study area (not to scale) showing the location of the sampling site on the
grounds of the Bayamon Carcel and the nearest industrial facility upwind in Catano.
Figure 2. Consecutive laboratory analyses of audit standard using GC/FID+ECD before the study (red),
followed by GC/MSD after the study (green), showing the first 21 (of 41) compounds to elute.
Figure 3. Consecutive laboratory analyses of audit standard using GC/FID+ECD before the study (red),
followed by GC/MSD after the study (green), showing the last 20 (of 41) compounds to elute.
Figure 4. Replicate field analyses of the audit standard by CMS MINICAMS, showing data for each of the
four compounds for which it was calibrated during the study and contrasted with results of laboratory
analyses of the audit standard by GC/FID+ECD before the study (red) and GC/MSD after the study (green).
Figure 5. Replicate field analyses of the audit standard by HNU Model 311, showing data for each of the four
compounds for which it was calibrated during the study and contrasted with results of laboratory analyses of
the audit standard by GC/FID+ECD before the study (red) and GC/MSD after the study (green).
Figure 6. Averages of the absolute differences between TO-14 reference results and PGC field results (red
lines). Centered upon the averages are bars, the lengths of which represent the standard deviations of the
absolute differences.
Figure 7. Averages of the differences between TO-14 reference results and PGC field results. The lengths of
the bars represent the average of the differences. Negative differences tend to cancel positive differences,
revealing a slight negative bias in five of eight cases and a slight positive bias in the other three.
Figure 8. Average retention times and their standard deviations. The length of each bar represents average
retention time. The widths of the red boxes at the ends of the bars are proportional to the standard deviations
of the retention times.
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Field Comparison of Portable Gas Chromatographs with Method TO-14
Richard E. Berkley and Maribel Colon
US Environmental Protection Agency, Research Triangle Park, NC 27711
Jesus Gonzalez and Israel Droz
University of Puerto Rico School of Public Health, San Juan, PR 00936
Jeffrey Adams, Christopher Fortune, and Karen Oliver
ManTech Environmental Services, Research Triangle Park, NC 27709
Daniel R. Coleman, CMS Research Corporation, Birmingham, AL 35244
Clayton Wood, HNU Systems, Incorporated, Newton, MA 02161
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TECHNICAL REPORT DATA
(Hast fttdInttrutHont on iHt rtvtnt btfort
. REPORT NO.
EPA/60O/A-94/045
I. TITLE ANDSUSTITLl
Field Comparison of Portable Gas Chromatographt
with Method TO-14
I. REPORT BAT!
I. PERFORMING ORGANIZATION CODE
AUTHORIS)
R E Berkley, M Colon, J Gonzalez, I Droz,
J Adams, C Fortune, K Oliver, D R Coleman, C Wood
I. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME AND ADORES*
US EPA/AREAL/MRDD/AMRB/RTP, NC
10. PROGRAM ELEMENT
Y105C A04 04
11. CONTRACT/BRANT NO.
CR - 817123-02-0
12. SPONSORING AOINCT NAME AND AOOREM
1J.TVPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/09
It. SUPPLEMENTARY MOTES
It. ABSTRACT
'-"A field-deployable prototype fast gas chromatograph (FGC) and two cotmnercially-
'"' Available portable gas chromatographs (PGC) were evaluated by measuring organic
vlpors in ambient afr at a field monitoring site in metropolitan San Juan, Puerto
Rico. The data were compared with simultaneous grab samples which were
collected in six-liter Summa-polished canisters and analyzed by method TO-14.
Because of fluctuating retention times, the FGC produced no useable data High
humidity levels may have adversely affected its performance. Both commercially
available PGCs performed successfully, and data from twenty analyses were compared
with the reference method. ' .
IT.
KIT WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTlPIERS/DPEN ENOEO TERMS
COSATi Field/Croup
ซ. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
tt. SECURITY CLASS
UNCLASSIFIED
""0-
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