EPA/600/A-93/085
Essential Capabilities of a Portable Gas Chromatograph *
Richard E. Berkley
US Environmental Protection Agency
Research Triangle Park, NC 27711
ABSTRACT
Volatile organic compounds in ambient air are usually estimated
by trapping them from air or collecting whole air samples and return-
ing them to a laboratory for analysis by gas chromatography using
selective detection. Data do not appear for several days, during
which sample integrity could become compromised. Immediate data can
be obtained, and sampling errors minimized, by analyzing with a field-
deployable instrument at the time samples are collected. Portable gas
chromatographs are available, but they don't fully meet the need for
guick, high-guality data under field conditions. Shortcomings include
insensitive detectors, non-selective detectors, poor resolution,
retention time drift, maladroit data processing schemes, excessive
energy consumption, and vulnerability to weather. Improved
waterproofing, temperature regulation, and energy efficiency are
particularly crucial to true field-deployability. Such improvements
are probably feasible. Mass spectrometric detection, high-speed
chromatography, polycapillary chromatography, and peak modulation may
lead to useful enhancements in future.
This paper has been reviewed in accordance with the U.S. Environ-
mental 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
Analysis of volatile organic compounds in air is usually perform-
ed on samples which have been collected in the field and transported
to a laboratory. Samples are collected by trapping analytes on sor-
bents or by collecting whole air samples in canisters. Analytes are
separated from the sample matrix by thermal desorption from sorbent
media or by cryogenic preconcentration from the whole air samples.
Then gas chromatographic analysis is performed using a selective de-
tector. Mass spectrometric detectors are especially effective because
they can detect most compounds selectively. Other specific detectors,
such as electron capture or photoionization, may be used to achieve
greater sensitivity [1]. Analyzing samples in a laboratory makes it
possible to apply sophisticated techniques which yield data of good
accuracy and precision. The data define the condition of samples at
the time they were analyzed, but not necessarily at the time they were
collected. Disadvantages are that sample integrity could become com-
promised during collection or storage, and data are not available for
days to weeks after sample collection. Analyzing samples with a
field-deployable instrument as soon as they are collected could fin-
esse those problems. "Field-deployable instruments" are essentially
* This paper is based in large part upon a paper presented at the On-
site (Analysis) Field Portable Instrumentation Conference of the
Seventh International Forum on Process Analytical Chemistry held at
Galveston, TX in January, 1993. It is a slightly expanded version of
the paper which was published in the proceedings of that conference.

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self-contained units which can readily be lifted by one or two people.
They are convenient to deploy at remote sites, require minimal logis-
tical support, and can be shipped routinely by common carrier. By
contrast, instruments permanently mounted in vehicles, mobile labora-
tories, and instruments which must be operated in on-site laboratories
are not field-deployable instruments.
Commercially-available portable gas chromatographs (PGC) are the
field-deployable instruments most often used to analyze volatile
organic compounds in air [2], The number of samples which one PGC can
analyze at a field site far exceeds the number which can be sent to a
laboratory for analysis because PGCs work faster and because they
discard samples as they analyze them, keeping only the data. Prompt
access to data and increased volume of data can help to characterize
hazardous waste sites, chemical spills, and other unknown and poten-
tially-hazardous sources of volatile organic compounds in air. They
can also optimize the selection of samples to be collected for later
laboratory analysis.
PORTABLE GAS CHROMATOGRAPH PERFORMANCE PROBLEMS
PGCs are not used as often or as effectively as they could be
because they don't perform as well as laboratory instruments and
because the advantages they offer are not well understood. PGCs do
have inherent disadvantages. Most are not equipped for programmed-
temperature chromatography because of constraints on size, weight, and
power consumption. Since isothermal chromatograms cannot separate as
many compounds, fewer compounds can be analyzed per run. Resolution
may also be inferior to that of laboratory instruments. Some
commercially-available PGCs suffer from inadequate design or shoddy
components. Operators become discouraged, and loss of confidence in
the instrument does not militate for greater proficiency. As a
result, PGCs have been taken less seriously than they should be. When
operated properly, they can produce data of good quality which can be
meaningfully compared to data from laboratory analysis of concurrent,
colocated samples [2,3].
Changes in instrument design and operating procedures are needed
to bring the performance of commercially-available PGCs up to full
potential. The performance of laboratory chromatographs may never be
equalled, but there is no reason to accept less than achievable
performance. Two changes which are not immediately needed are better
capillary columns and smaller instruments. Presently-available
capillary columns are adequate, and presently-available PGCs are
smaller and lighter than they need to be. Most of them can be lifted
with one hand, but connections to utilities, sample inlets, and data
devices tie them down during operation. "Hand portable" or "pocket"
instruments have limited use. They can locate "hot spots" at
uncharacterized sites, if they are "hot" enough. That done, what is
needed is to find out quickly which toxic compounds are present and
how much of each. Hand-held instruments cannot do that, and labora-
tory analysis takes too long. An analytical instrument performing on-
the-spot analyses would be ideal, even one larger, bulkier, and more
costly than present-day commercially-available PGCs.

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Design Problems
When a PGC is unable to perform at full potential, it is usually
because it was designed by people who don't use it, and compromises
were made in choosing components to reduce size and cost.
Chromatographic Resolution. It is not necessary to use low
quality flow system components, though it may seem expedient to do so.
PGCs usually have lower resolution than laboratory instruments because
they use shorter columns to reduce analysis time, but too often the
other parts of the flow system are more rudimentary than the column.
Resolution is degraded by solenoid valves if they are too large for
the column or if they stick or leak, and active surfaces cause peak
tailing. A selective detector can partially compensate for poor
chromatography, but the number of compounds that can be analyzed is
reduced, and so is accuracy.
Detectors. Some PGC detectors are insensitive or non-selective,
for example, thermal conductivity and flame ionization. Using such
"universal detectors" does not make it possible to analyze more com-
pounds. They are relatively insensitive and may not notice trace
amounts. Since no chromatograph can separate all the contaminants in
ambient air, each peak generally contains two or three compounds, so
identifications based on retention times using nonselective detectors
are unreliable. If a detector cannot distinguish between coeluting
compounds, then the "information" it provides is misleading, and its
only real capability will be running calibration standards. A PGC
detector needs to be both sensitive and selective. Photoionization
and electron capture detectors meet these criteria and can readily be
operated in the field. Simultaneous use of more than one kind of
selective detector would increase the number of compounds which could
be analyzed in each run. Mass spectrometers are more difficult to
operate in the field, but the advantages they offer might make the
extra trouble worthwhile.
Carrier Flow Control. Poor flow control causes variable
retention times and unstable baselines. Many PGC manufacturers use
needle valves to regulate carrier gas flow. Ordinary needle valves
are rarely considered adequate for laboratory chromatographs, even
though they usually operate in quiet, clean environments. Why expect
a needle valve to cope with the jolts, vibrations, and contamination
which are encountered in field operation?
Weatherproofina. Fluctuations in column temperature destabilize
baselines and retention times. Worse yet, relative retention times
change with temperature, compounding the chaos. Constant temperature
is critical not only to column performance, but also to proper func-
tion of electronic components, especially signal-processing. Oven
insulation in PGCs is sometimes perfunctory, and usually electronic
components are not insulated at all, even though they must operate in
environments where ambient temperature range is broad and access to
line power is limited. At the first chill breeze, retention times go
up, the baseline goes down, and response factors decrease. The ovens
of laboratory chromatographs are usually well insulated, but they
still use plenty of line power to control temperature. Temperature
stability of their electronic components is left to the heating/cool-
ing system of the laboratory building. If electronic components get
too cold or too hot, performance suffers. Why build less temperature

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control into a field-deployable instrument when it actually needs
more? And why build a field-deployable instrument that will be ruined
if it is left out in the rain?
Power Requirements. An instrument which must be plugged into a
power outlet is useless without the power outlet. Instrument desig-
ners who believe that field operators cannot lift more than twenty
pounds will not likely think of using a full-size 12 volt battery, but
the weight is not significant unless there is a long walk to reach the
site. Sites which are accessible to vehicles but have no line power
are more common than hike-in sites which do have line power. Twelve
volt batteries are generally more reliable than the line power at
remote sites, and they are easier to obtain. Gel-cell batteries can
be shipped by air. Marine batteries can be completely discharged many
times without damage. They provide 80 to 100 ampere-hours, ample
power for most instruments. If more power is needed, more batteries
can be connected. It is probably easier to suppress electrical noise
in an instrument which operates on 12 volt DC power. If a battery is
connected to a 12 volt DC instrument while it is operating on line
power, the instrument can charge the battery. Then in event of a
power failure, the battery can supply power to the instrument. Port-
able generators offer an alternative, but they have their own disad-
vantages, including the possibility of contaminating the site with
exhaust.
Microprocessor Control. Many PGCs are controlled by internal
microprocessors. Too often they turn out to be too small to accom-
modate the multitude of schemes for exploiting them which come to mind
after they have been selected. It would be better to design an in-
strument to be driven by an external laptop computer or even to build
a computer into the instrument. A full-size computer memory would be
capable of accommodating the kind of sophisticated peak recognition
and measurement algorithms which are used in laboratory instruments.
That would decrease the need for hand correction of misidentified
peaks and "bad integrations". At least one manufacturer has already
done this.
Data Processing. Some PGCs have built-in data-processing schemes
which inhibit or even prevent the operator from choosing a preferred
format for data tabulation. Access to data may be delayed, and data
quality may even be impaired. At a minimum, the operator should be
able to receive data on disk in a form which can be processed by
standard data-reduction software. Hand-copying data is unacceptable
because it risks contamination by human fingerprints.
snwiniaT-y of Performance Problems. Most design problems result
from compromises which are intended to enhance portability or reduce
cost. There is no good reason for some of them to occur at all.
Eliminating others will require substantial redesign. A few are
inherent in portability and must be endured. Manufacturers can best
work to mitigate functional problems by paying careful attention to
how their products are used and periodically redesigning them to fit
their real-world applications. Going off in a corner to invent cute-
but-trivial new features may not improve sales. The most pressing
problems don't call for great technological forward leaps; they should
be tractable with current technology.

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POTENTIAIaLY USEFUL INNOVATIONS
There are several enhancements to gas chromatographic technique
which might be applicable to field deployable instruments,* however,
none of them are specifically limited to portable instruments, nor are
they potential remedies for poor design or inferior components.
Mass Spectrometric Detectors
Mass spectrometers have long been used as gas chromatograph
detectors. They are highly selective for most compounds and can often
identify unknown compounds unequivocally, even when they coelute.
There is at least one commercially-available field-deployable mass
spectrometer which has a gas chromatograph attached to it. It can be
lifted by two men and shipped as excess baggage on an airplane. It
requires line power. If this instrument is sensitive enough, it could
do on-the-spot quantitative analysis. If not, it might still validate
data produced by other FGCs by positively identifying compounds.
High-Speed Chromatography.
Levine has developed a field-deployable high-speed gas chromato-
graph which completes a chromatogram in less than one minute [4,5]. A
specially-designed monel cryofocusing loop is heated by capacitive
discharge to inject samples onto a capillary column, typically 0.25 mm
inside diameter and 10 m long. Injection bandwidth is 10 msec, and
carrier flow velocity is 60 to 175 cm/sec. A specially-adapted detec-
tor must be used to distinguish between peaks and electrical noise and
to ensure that the outlines of peaks are well-defined. Detector res-
ponse must be extremely fast, so conventional noise filtration cannot
be used. This instrument has been successfully operated with flame
ionization, electron capture, and photoionization detectors. Resolu-
tion is not compromised, and separations are enhanced by the narrow
bandwidth of the injections. Sensitivity is also increased because
narrow peaks are taller. As a result, it is possible to detect anal-
ytes at low part per billion concentrations in whole air samples of
0.25 - 5 ml. Disadvantages include use of line power and liquid nit-
rogen. Also, trace contaminants in the carrier gas tend to build up
in the capillary trap, because it is cooled continuously between capa-
citive discharges. This instrument will be field tested during 1993.
Polycapillary Gas Chromatography
Grachev and coworkers at the Limnological Institute in Irkutsk,
Russian Federation have designed a fast gas chromatograph that uses a
multitude of parallel glass capillaries which are close-packed inside
a hexagonal sheath which is about 6 cm in diameter [6]. A schematic
of its cross-section is shown in Fig. 1. Typical column length is
20 cm, and retention times for many compounds of low volatility, pes-
ticides for example, are less than five minutes. Resolution is poor,
but might be improved by changes in the injection system. This
technology, referred to as polycapillary gas chromatography, may
eventually be useful for analysis of high-molecular-weight compounds,
especially pesticides.
Peak Modulation.
If a microbore capillary column were used, column length could be
reduced in proportion to bore diameter. Some scale reduction could
also apply to analysis time. It is difficult to make an accurate in-
jection onto a microbore column without flooding it. Phillips has
found a practical way to do this using a peak modulator to chop
samples of ordinary size into miniature aliquots as they emerge from a

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capillary column of ordinary diameter [7-9], The peak modulator con-
sists of a short length at the downstream end of the capillary column
which is coated with electrically-conducting paint. Electrical leads
are attached to each end of the conductive section. When a pulse-
sequence electric current is applied, the modulator is rapidly heated
by each pulse and quickly cools to ambient temperature between pulses
due to its low heat capacity. Each pulse expels from the modulator
whatever analyte material has entered it since the last pulse. It
departs the modulator in a narrow band and immediately enters either a
microbore column or a detector. Setting up a peak modulator can be
tedious, but that is not much of a problem if the same procedure is
repeated indefinitely, as is typical of PGC applications.
One-Dimensional Microbore Capillary Chromatography. To inject a
sample onto a microbore analytical column, the modulator is placed at
the end of a short length of ordinary capillary column and connected
directly to the head of the microbore column [7,8]. Flow is not
split, so flow velocity is faster in the microbore column. Injection
is made onto the short capillary, through which the sample travels at
normal (relatively slow) velocity. As the injection band enters the
modulator it is chopped into a sequence of miniature aliquots which
pass through the microbore column at much higher velocity and are seen
by the detector as a sequence of fast chromatograms. These are added
together to produce a single chromatogram. This process is shown
schematically in Fig. 2. In effect, the microbore column has analyzed
a large sample in a few minutes without becoming overloaded. It
produces a high-resolution chromatogram which would have taken much
longer using a larger column.
Two Dimensional Microbore Capillary Chromatography. A peak
modulator placed at the downstream end of a full-length large-bore
capillary column will chop effluent into aliquots. Further separation
is done on a microbore column immediately downstream which uses a
different stationary phase. The resulting two-dimensional chroma-
togram can achieve separations which are impossible using a single
column [9]. The process is shown schematically in Fig. 3, and a two-
dimensional chromatogram is shown in Fig. 4.
Enhancement of Late-Eluting Peaks. A modulator can be placed at
the end of an analytical column, just before the detector, as shown in
Fig. 5. The peak of any compound which has affinity for the station-
ary phase in the modulator will be chopped into a series of tall, nar-
row peaks, the tops of which trace the outline of a peak which has the
same width but is much taller than the original. This effect, shown
in Fig. 6, increases as peaks become shorter and broader toward the
end of a chromatogram, and it tends to rescue them from merging with
the baseline, which is particularly a problem on isothermal chromato-
grams. The kind of stationary phase in the modulator will determine
which classes of compounds are enhanced and which are not.
CONCLUSIONS
Portable gas chromatograph performance has made great progress in
the last 20 years. At present they can produce reliable on-site data
rapidly, given adequate shelter, power, and operator skill. They are
no longer novelties, but they are temperamental under adverse condi-
tions, and some design modifications seem appropriate:

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o PGCs are already easier to transport than necessary. Some porta-
bility could be sacrificed to solve other problems. An instrument
which one person can stuff into the back seat or the trunk of a car
would be portable enough, if it performed well in the field.
o Randomized retention times, peregrinating baselines, and wilting
response factors are intolerable. Gas chromatographs operate best
with column and electronic components at constant temperature. Field-
deployable instruments need to be self-sufficient as to temperature
stability. PGC columns generally operate isothermally, so why not
enclose the entire system in an insulated and thermostatted box?
Thermal leakage from electronic components and the (separately-insula-
ted and thermostatted) column enclosure could provide auxiliary heat.
o Field deployable instruments should be rain-proof.
o Field-deployable gas chromatographs should be able to operate on
battery power for at least eight hours, but preferably twenty-four
hours.
o A major incentive to use a field-deployable instrument is to get
quick and easy access to data. Any design feature which hinders data
access is undesirable, no matter how attractive.
o The ideal PGC would perform as well in the field as it does in
the laboratory.
o Once the performance of a PGC has been optimized, consideration
should be given to integrating into it features such as mass spectro-
metric detection, high-speed chromatography, polycapillary columns,
and peak modulation.

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REFERENCES
1.	Compendium of Methods for the Determination of 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.	R. E. Berkley, M. Miller, J. C. Chang, K. Oliver, C. Fortune,
Evaluation of Commercially-Available Portable Gas Chromatographs, in
Proc. 1992 EPA/AWMA International symposium on Measurement of Toxic
and Related Air Pollutants, Air and Waste Management Association,
Pittsburgh, PA, 1992.
3.	R. E. Berkley, J. L. Varns, and J, Pleil, Environ. Sci. Techno1.,
25 (1991) 1439.
4.	H. K. 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.
5.	H. K. 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.
6.	T. Bidleman, Atmospheric Environment Service, Environment Canada,
4905 Dufferin Street, Downsview, Ontario M3H 5T4, Canada, personal
communication, 1992.
7.	Zaiyou Liu, J. B. Phillips, "Sample Introduction into a 5
micrometer i. d. Capillary Gas Chromatography Column Using an On-
Column Thermal Desorption Modulator," J. Microcolumn Sep., 1 (1989)
159.
8.	Zaiyou Liu, J. B. Phillips, "Large-Volume Sample Introduction into
Narrow-Bore Gas Chromatography Columns Using Thermal Desorption
Modulation and Signal Averaging," J, Microcolumn Sep., 2 (1990) 33.
9.	Zaiyou Liu, J. B. Phillips, "Comprehensive Two-Dimensional
Chromatography Using an On-Column Thermal Modulator Interface," J.
Chromatogr. Sci., 29 (1991) 227.
10.	J. B. Phillips, Department of Chemistry and Biochemistry, Southern
Illinois University, Carbondale, IL 62901-4409, personal
communication, 1993.

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Figure 1. Cross-section of a polycapillary column. Length 20 cm,
width approximately 6 mm. Not drawn to exact scale. The number of
capillaries is greater than shown.

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¦
I
MEGABORE 	
PRECOLUMN INJECTOR
MICROBORE
ANALYTICAL
COLUMN
Figure 2. Schematic drawing of a large volume injection into a
microbore capillary column showing four representative micro-
chromatograms and the sum of them. The number of micro-
chromatograms is actually much larger. Not taken from actual data,

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INJECTOR
FIRST
CAPILLARY
COLUMN
SECOND\
(M1CROBORE )\
CAPILLARY COLUMN
Figure 3. Schematic diagram showing use of peak modulation to
produce a two-dimensional chromatogram.
• 13 ¦
4200
r
4S00	5100
First Dimension R*t»rrtion Tim# (mc)
T
5700
Figure 4. Section of a two-dimensional chromatogram produced by
peak modulation [10]. Peaks are seen from above.

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CAPILLARY
COLUMN
NJECTOR
~
DETECTOR
Figure 5. Schematic diagram showing use of modulation to enhance
late-eluting peaks.
Figure 6. The effect on a late-eluting peak of a peak modulator
placed just before the detector. The shaded area of the original
peak forms the dark enhanced peak. This geometric construction
is not taken from actual data.

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TECHNICAL REPORT DATA
(Pteeif read Instruct torn on the t event before compter
t. REPORT MO
EPA/600/A-93/085
4. TIT IE AND SUBTITLE
FIELD-DEPLOYABLE MONITORS FOR VOLATILE ORGANIC
COMPOUNDS IN AIR
6 REPORT DATE
B. PERFORMING ORGANIZATION CODE
7 AUTMORIS)
R. E. Berkley
• PERFORMING ORGANIZATION report no
10.	PROGRAM ELEMENT NO.
Y105C/AQ4/F01
11.Ł6NfAAŁT/dftANt	n6.
9 PERFORMING ORGANIZATION NAME AND ADDRESS
US EPA Atmospheric Research and Exposure Assessment
Laboratory
MD-75
Research Triangle Park, NC 27711
68-D8-0002
68-D0-0106
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
Conference proceeding 1993
I*. SPONSORING AGENCY COD!
EPA/600/09
IS SUPPLEMENTARY NOTES
16. ABSTRACT
Volatile organic compounds in ambient air are usually estimated by trapping then
from air or collecting whole air samples and returning them to a laboratory for
analysis by gas chromatography using selective detection. Data do not appear for
several days, during which sample integrity could become compromised. Immediate
data can be obtained, and sampling errors minimized, by analyzing with a field-
deployable instrument at the time samples are collected. Portable gas chromatographs
are available, but they don't fully meet the need for quick, high-quality data under
field conditions. Shortcomings include insensitive detectors, non-selective
detectors, poor resolution, retention time drift, maladroit data processing schemes,
excessive energy consumption, and vulnerability to weather. Improved waterproofing,
temperature regulation, and energy efficiency are particularly crucial to true field-
deployability. Such improvements are probably feasible. Mass spectrometric
detection, high-speed chromatography, polycapillary chromatography, and peak
modulation may lead to useful enhancements in future.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
IB. DISTRIBUTION STATEMENT
IB SECURITY CLASS (THu Report)
21. NO.

AGES
30 security class (Thu me)
22 PRICE
tf A ft** 2220.1 (R»«. 4-77! pkivioui ioition k obsolete

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