Analysis of volatile organic compounds using gas
chromatography

Jo Dewulf, Herman Van Langenhove*
Research Group Environmental Chemistry and Technology, Department of Organic Chemistry,
Faculty of Agricultural & Applied Biological Sciences, Ghent University, Coupure Links 653,
B-9000 Ghent, Belgium

Gyula Wittmann
Department of Inorganic and Analytical Chemistry, Faculty of Science, University of Szeged,
Do

´m Te´r 7, H-6701 Szeged, Hungary

The focus of this review is the analysis of volatile
organic compounds (VOCs) by gas chromatography
(GC) in the field of environmental, food, flavour and
fragrance, medical and forensic sciences. New trends
in sample injection, separation and detection are
covered, including multi-dimensional and high-speed
GC. Attention is drawn to a growing interest in
quality assessment. From the review, it is clear that
it remains a challenge to generate multi-component
gaseous standards of VOCs at ppbv and pptv. #
2002 Published by Elsevier Science B.V. All rights
reserved.

Keywords:

Gas chromatography (GC); Volatile organic com-

pounds (VOCs)

1. Introduction

VOCs are a topic of interest in many disciplines,

such as food, flavour and fragrance, medical and
forensic sciences. The main area dealing with
VOCs may be environmental chemistry, because
VOCs contribute to stratospheric ozone deple-
tion, tropospheric ozone formation, toxic and
carcinogenic human health effects, etc.

It is worth mentioning that there is no agree-

ment about the definition of VOCs. In spoken
language, VOCs are often used as synonyms for

organic solvents. An effect-oriented definition,
mainly used in the USA, states that VOCs are
all organic compounds contributing to photo-
chemical ozone creation. More general defini-
tions are based on physical and chemical
properties of the compounds, such as chemical
structure, boiling point, air/water partitioning,
and vapour pressure.

Frequently used are definitions based on

vapour pressure. In the USA, VOCs are defined
as organic compounds that have a vapour pres-
sure more than 13.3 Pa at 25

C, according to

ASTN test method D3960–90. In the European
Union, a common definition is that VOCs are
organic compounds with a vapour pressure
above 10 Pa at 20

C (European VOC Solvents

Directive

1999/13/EC).

The

Australian

National Pollutant Inventory defines a VOC as
a chemical compound based on carbon chains
or rings (and also containing hydrogen) with a
vapour pressure greater than 2 mm of mercury
(0.27kPa) at 25

C, excluding methane.

Whatever the definition taken, it is obvious

that all research areas dealing with VOCs have
made progress based on analysis by GC. Ana-
lysis of VOCs by means of other techniques is
rather limited. Examples of these techniques
include DOAS (differential optical absorption
spectroscopy) for gaseous BTEX (benzene, tol-
uene, ethylbenzene and xylenes) and formalde-
hyde, and MIMS (membrane introduction mass
spectrometry) for gaseous and liquid samples.

0165-9936/02/$ - see front matter

# 2002 Published by Elsevier Science B.V. All rights reserved.

P I I : S 0 1 6 5 - 9 9 3 6 ( 0 2 ) 0 0 8 0 4 - X

trends in analytical chemistry, vol. 21, nos. 9+10, 2002

637

*Corresponding author. Tel.: [phone]; Fax: +32 9

264 62 43.

The objective of this review is to focus on

analytical procedures for determination of
VOCs by GC. VOCs analysis, whether in a
gaseous, liquid or solid matrix, usually starts
with pre-concentration of VOCs. A number of
recent review papers can be found dealing with
pre-concentration through solid sorbents, cryo-
genic pre-concentration, membrane devices, sol-
vent extraction, static and dynamic headspace,
solid phase micro-extraction (SPME), stir-bar
sorptive extraction (SBSE), supercritical fluid
extraction (SFE) and distillation and sublima-
tion techniques. General reviews are from
Majors [1], environmental-oriented papers are
from Clement et al. [2,3], Fox [4], Richardson
[5], Dewulf and Van Langenhove [6–8] and
Helmig [9]. In the field of flavour analysis,
reviews on wine aroma [10], volatiles from cer-
eals [11] and food flavours [12] have to be
mentioned. Finally, a number of reviews focus
on specific pre-concentration techniques, such
as headspace techniques [13], sorbent trapping
[14] and SPME [15–18].

Pre-concentration techniques have to take

into account the polarity of the target analytes,
especially

sorbent-based

techniques.

Water

interference is a special issue that requires
attention. Recent papers focusing on water
removal [3,6–8,13] discuss techniques based on
selecting hydrophobic sorbents and/or introduc-
ing hygroscopic salts, water-sorbing polymers
(Nafion) and dry purge stages.

In this review, emphasis will be put on the

GC-analysis itself, i.e. sample injection, separa-
tion, detection and analytical quality assurance
and control. Attention will mainly be paid to
developments of the last two to three years. The
basis of the work is three-fold:

. a thorough screening of Analytical Abstracts (Silver

Platter International) for the period January 1999-
August 2001;

. study of the review issues of Analytical Chemistry

of 1999-2001 [2-5,19-24]; and,

. use of an in-house database on environmental

VOC analysis, built up during the last 10 years and
comprising 979 articles.

2. Sample injection

Sampling and pre-treatment end up with tar-

get VOCs in different physical states. Being
gaseous, dissolved in a liquid, trapped cryogeni-
cally or adsorbed on a solid material, VOCs
have to be brought onto the GC column. Some
recent reviews include a discussion of VOCs
sample injection [6–9,12–18,25].

Injection of liquid or gaseous samples is typi-

cally carried out by syringes and sample loops,
employing on-column, split and split less injec-
tion. For solvents, large volume injection has
been developed in order to improve limits of
detections. A major difficulty with large-volume
liquid injections of VOCs is the limited differ-
ence in volatility between solvent and analytes.
Recent strategies to overcome this difficulty are
reported [26–29]. Boselli et al. [26] inserted
restrictions between the uncoated precolumn and
the vapour exit so that solute accumulation at the
front of the flooded zone was avoided. The
accumulation at the front was the result of a
strong pressure drop over the flooded zone owing
to liquid plug formation. Hankemeier et al. [27]
and Adahchour et al. [28] describe a strategy in
which the evaporation rate is determined by
increasing the injection time at a fixed injection
speed, injection temperature and head pressure.
The measurement of the flow rate in the carrier-
gas supply line to the on-column injector allowed a
rapid optimisation: some five injections proved to
be sufficient. Another possibility is called ‘‘inverse
large-volume injection’’, where a semi-volatile sol-
vent elutes after the target compounds [29].

Pocurull et al. [30] designed a special swing

injection system for introducing large volumes
of water-containing samples. Sample evapora-
tion and solvent-solute separation were per-
formed separately by a set-up consisting of two
PTV (programmed temperature vaporization)
injectors filled with different sorbent materials
and kept at different temperatures. The design
allows analysis of target compounds with a wide
range of volatilities present in water-containing
liquid samples (Fig. 1).

Whereas

cryogenically

pre-concentrated

VOCs can be injected in a narrow band, release

638

trends in analytical chemistry, vol. 21, nos. 9+10, 2002

of targets from a solid sorbent by means of
thermal desorption results in band broadening.
Traditionally, cryogenic refocusing after thermal
desorption, carried out in front of the injector,
overcomes this problem. This solution compli-
cates the analytical procedure and equipment,
contributing to higher variances and risks of
errors. Attempts to simplify solid-sorbent desorp-
tion are found in recent literature, simulta-
neously speeding up the pre-concentration and
offering on-line analysis capabilities. In a first
set-up, refocusing is done within the GC
injector on a cold column head. A second
approach involves thermal desorption of min-
iaturized traps. Typical examples here are des-
orption of SPME-fibers [13,15–18] and PTV-
injectors [31–34] and narrow-bore capillaries
[35,36], the latter two both filled with sorbent
material.

3. Separation

In the past, VOCs have typically been sepa-

rated on capillary columns, mainly silicone-type
Wall Coated Open Tubular (WCOT) and alu-
mina-based

Porous

Layer

Open

Tubular

(PLOT) columns for highly volatile compounds.
More recently, there have been some new
trends in the separation technology.

3.1. Recent column developments

Silicone-based columns are commercialised

under different names, e.g. AT-1, EC-1, CP-
Sil5CB, DB-1, BP-1, HP-1, OV-1, RSL-150,
RTX-1, SPB-1 and MXT-1, for 100% poly
dimethylsiloxane. Over and above these multi-
purpose columns, manufacturers offer columns
specially designed for VOCs analysis according
to EPA methods, e.g. VOCOL, RTX-VMS,
RTX-VGC, RTX-VRX and DB-VRX. The
design, with aid of computer modelling [37], is
driven to shorten analysis times through higher
peak capacities; analysis of 66 targets in 30 min-
utes on a WCOT column [38] and 15 targets in
16 minutes on a PLOT column [39] have been
reported. Preparation, applications and future
directions of PLOT capillary columns have
been reviewed by Ji et al. [40]; extension of
PLOT applications by improving the thermal,
mechanical and chemical stability of the column
has been reported [41]. PLOT column applica-
tions for oxygenated compounds in air have
been published [42]. Zeng et al. [43] fabricated a
capillary column with crown-ether-based sta-
tionary phases, through a sol-gel process and
coating onto the inner wall of a fused silica
capillary. The columns showed high selectivity
for the separation of positional isomers of aro-
matic compounds. Recently, Mangani et al. [44]
used a Graphite-Lined Open Tubular (GLOT)
for BTEX analysis.

In the analysis of biogenic VOCs (especially

terpenoids), flavour and fragrances, there have
been reviews of the use of chiral cyclodextrin-
based stationary phases [45,46].

In most applications, separation of VOCs is

based mainly on the interaction with the stationary

Fig. 1. The sample-introduction and the desorption modes
of the swing system designed to introduce large water-con-
taining liquid samples with a wide range of volatilities
(From [30]).

trends in analytical chemistry, vol. 21, nos. 9+10, 2002

639

phase, since interactions with mobile phases,
such as He, N

2

or H

2

, are negligible. Recently,

Berezkin et al. [47,48] reported a technique in
which specific gases or vapours are used in the
mobile

phase.

In

this

‘‘acidic-basic

GC’’

(ABGC), the apparent degree of dissociation of
volatile acidic or basic VOCs in the stationary
liquid phase is influenced by the gases or
vapours, e.g. amines and ammonia, introduced
to separate carboxylic acids.

3.2. Multi-dimensional separation

Multi-dimensional – two-dimensional (2D) –

separation has been developed in order to
overcome the peak overlap experienced in one-
dimensional chromatograms of complex mix-
tures [49]. The 2D concept has been reviewed
recently [50–52]. Applications of 2D analysis of
volatiles are mentioned for air analysis [9], petro-
chemicals [53] and flavours [45]. The separation

power of 2D GC for volatiles is impressive:
about 550 individual peaks of compounds
within the C

6

-C

14

range are isolated in one run

[54]. An illustration is given in Fig. 2 for an
urban air sample. The huge number of species
was here further classified using retention
behaviour, indicating about 100 multi-sub-
stituted aromatics and 50 carbonyls, along with
many hundreds of aliphatic hydrocarbons.

In a typical configuration, a polar second col-

umn performs the separation of portions from a
first, non-polar column with a periodicity of
seconds [19]. Although there are, in principle,
valve and thermal modulation, only thermal
modulation is considered to be really compre-
hensive [55]. Thermal modulation can be car-
ried out by both heating and cooling, as
represented schematically in Fig. 3. The mod-
ulator, passing effluents from the first column
as sharp pulses suitable for high-speed chroma-
tography onto the second column, is the critical

Fig. 2. Sections of 1D and 2D chromatograms of an urban air sample. About 15 peaks can be observed in the single-column 1D
chromatogram; the comprehensive 2D chromatogram shows around 120, with discrimination between aliphatics (band 1),
carbonyls (band 2) and aromatics (band 3) (From [54]).

640

trends in analytical chemistry, vol. 21, nos. 9+10, 2002

Fig. 3. Schematic representation of heated and cryogenic modulation. Heated modulation with (1) trapping of solutes; (2)
remobilisation of solutes; (3) continuous refocusing of solutes and trapping of next fraction; and, (4) release of solutes.
Cryogenic modulation with (1) trapping of solutes; (2) release of solutes; (3) separation and next trapping. (From [55]).

trends in analytical chemistry, vol. 21, nos. 9+10, 2002

641

device in 2D GC [22]. Leonard and Sacks [56]
report that 2D fast GC with time-of-flight mass
spectrometry (TOFMS) can collect 500 spectra
per minute, thus allowing very short analysis
times, since overlapping peaks can be tolerated.
2D comprehensive liquid chromatography-gas
chromatography (LC-GC) for volatiles, with LC
separations in the 5–10 minute range and GC
separations in the 1–2 second range, has been
reported [57]. This comprehensive LCGC
instrument, with 100% water mobile phase
in the LC stage, is an alternative to current
methods

that

employ

headspace

analysis.

Separations of compounds such as BTEX, as
well as chloroform and methylene chloride are
presented.

3.3. High-speed GC

Since the late 1990s, reduction of GC analysis

time has resulted in high-speed GC (HSGC), or
fast, rapid or ultra-fast GC (for a report, see
Sacks et al. [58], for reviews, see [22,59–62], and
for theory on HSGC, see Blumberg [63–65]).
Hinshaw [62] distinguished four levels of speed
in capillary GC (Table 1). HSGC is char-
acterised by relatively short columns, small col-
umn

diameters

and

fast

temperature

programming, typically 50

C/min., all resulting

in analysis times of the order of seconds. The
high heat-up rates are based on resistive heating,
already described in the 1960s [66]. For fast-GC

analysis, the capabilities of this technology have
recently been investigated [67,68]; at the
moment, resistive heating systems for fast
GC, with heating rates up to 70

C/min., are

available [69].

Van Deursen et al. [70] investigated the use of

wide-bore columns for fast GC with vacuum
outlet, allowing a high sample capacity. A special
feature of HSGC is its capability for use in on-
line monitoring equipment in the field, when it
is combined with fast sample introduction sys-
tems. Typical applications are with SPME or
membrane-based sample pre-concentration for
air and water analysis, including portable instru-
ments [71–74]. Further on, the combination
with time-of-flight mass spectrometry (TOFMS)
looks very promising [52,75,76].

4. Detection

Capillary GC (CGC) analysis of VOCs typi-

cally employs FID (flame-ionisation detection),
MSD

(mass-spectrometry

detection),

ECD

(electron-capture detection), (D or H)ELCD
((dry or Hall) electrolytic conductivity detec-
tion), PID (photo-ionisation detection), FPD
(flame-photometry detection) and NPD (nitro-
gen-phosphorus detection). Recent detector
developments have been reviewed by Fox [5]
and Eiceman et al. [22]. Although VOC detec-
tion is still largely based on FID, MS and ECD

Table 1
Four levels of speed in capillary gas chromatography (CGC) [62]

Level

Description

Relative
speed of
analysis

Column dimensions

Inlet
pressure
(psig)

Injector

Detector

1

Conventional CGC

1

10–100 m0.18–0.53 mm

2–100

Conventional

Conventional

2

Rapid CGC on conventional
instruments

3–5

5–50 m0.18–0.53 mm

2–100

Conventional,
PTV* cold
trapping

Conventional,
sampling rates
at 50 Hz

3

High-speed CGC on
modified conventional
instruments or components

5–10

2–25 m0.10–0.25 mm

10–150
or higher

Rapid heating

Conventional,
sampling at
200 Hz

4

Very-high-speed CGC
on specialized instruments

10–50

2–10 m0.03–0.10 mm

20–200
or higher

High sensitivity,
high speed

*Programmed-temperature vaporizing.

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trends in analytical chemistry, vol. 21, nos. 9+10, 2002

(see e.g. [9]), new types are reported, such as
micro-ECD

[77],

HID

(helium-ionisation

detection, which is especially sensitive for oxy-
genates, when compared with FID) [78], MIP-
AES (microwave-induced plasma atomic-emis-
sion spectrometry) for halogenated VOCs [79],
SCD

(sulphur-chemiluminescence

detection)

[10] and RF-IMS (radio-frequency ion-mobility
spectrometry) [80].

Taking into account their selectivity, their

sensitivity and their ability to provide structural
information, detectors are connected in series or
in parallel at the outlet of the GC column in
order to get the maximum information. In
environmental applications, Koziel et al. [81],
for example, reported VOC analysis on a por-
table GC equipped with PID, FID and DELCD
in series. In flavour analysis, where typically
GC-olfactometry is utilized, sniffing ports and
FID have been configured in parallel [82]. GC
analyses of flavours have been compared
recently to direct sensors used without any
separation,

such as MS-based

and semi-

conducting polymer sensor-based electronic
noses [83–85]. Structural information is typically
provided by MS. Zhou et al. [11] have reported
the employment of FTIR and MS in series.

5. Analytical quality

In research papers, emphasis is mainly put on

novel developments. However, it is not common
practice to assess analytical performance by sys-
tematically giving data on limits of detection
(LOD), limit of quantification (LOQ), blank
levels, reproducibility, repeatability, accuracy,
calibration, specificity, and range of application.
Nevertheless, some recent papers do focus on
analytical performance [86–89]. Huxham and
Thomas [89] observed seven stages contributing
to errors and uncertainties in the determination of
VOCs concentrations in air (Fig. 4).

The ultimate test of performance is inter-

laboratory comparison. Such exercises have
been reported for the analysis of terpenes in air
[89], chlorinated VOCs in surface waters [88],
VOCs by SPME [90] and volatiles in beer [91]
and spirits [92]. Jurvelin et al. [93] discussed
typical problems experienced in multi-centre
studies of gaseous VOCs analyses. This study
shows the necessity for carefully planned and
realised quality control and quality assurance
(QC/QA) in multi-centre studies, where a
common sampling method and laboratory ana-
lysis technique is not used.

Fig. 4. Fault tree showing the principal modes of failure for VOC analysis using active sampling onto an adsorbent trap (From
[86]).

trends in analytical chemistry, vol. 21, nos. 9+10, 2002

643

One essential aspect in achieving high quality

in airborne VOCs analysis is the availability of a
calibration mixture [3,6,94]. Mixtures are usually
prepared in the laboratory itself by static or
dynamic dilution, whether starting from gaseous
mixtures or from liquids. Dynamic dilution is
typically done by diffusion through a membrane
(permeation) or through a capillary. Recently,
Gautrois and Koppmann [95] combined the use
of diffusion through a capillary with a second
dynamic dilution with pure air, down to pptv
levels, comprising a large range of VOCs and
showing a high linear dynamic range. Ethene
calibration starting from thermal decomposition
of a suitable surface compound has been
reported [96].

McKinley and Majors [94] question the trace-

ability to standards in airborne VOCs analysis;
more than 400 VOCs of environmental and
industrial interest can be measured, but trace-
level standards are available for only about 30
compounds.

Calibration of VOCs analysis based on equilib-

rium-based pre-concentration techniques, e.g.
static headspace or SPME, requires information
on the partitioning of the analytes between the
matrix to be analysed and the matrix to be
injected in the GC [13,16,97–99]. Namiesnik et
al. [16] discussed two approaches to calibrate
SPME-GC, based on knowledge of distribution
coefficients or on preparation of standard mix-
tures. Calibration of SPME fibers for air analy-
sis by means of mathematical modelling has
been proposed [100,101]. Murray [102] investi-
gated erratic calibration with SPME resulting
from competitive sorption with higher mole-
cular compounds coming from the matrix and
changing from sample to sample.

6. Conclusions and perspectives

The first trend apparent in current GC analy-

sis of VOCs is the attempt to reduce analysis
time. This is exemplified by the development of
miniaturized pre-concentration steps that can be
put on-line with the GC instrument, such as
sorbent-filled PTV injectors and SPME. How-

ever, high-speed GC is shortening GC separa-
tion from minutes to seconds.

Secondly, research is focussed on maximizing

the information one can get out of a sample.
Novel developments in this field are new column
technologies, e.g. chiral separations, and columns
especially designed for VOCs analysis. However,
progress might mainly be in the development of
2D GC. It will enable substantial progress in the
study of biogenic VOCs, the atmospheric fate of
VOCs, and flavour and fragrances.

Finally, quality assessment is a topic receiving

growing attention, as can be noticed from recent
research papers and published interlaboratory
comparison results.

A remaining challenge is the generation of

easily available and traceable gaseous standards
with dozens of target compounds at relevant
concentrations.

Acknowledgements

The authors acknowledge financial support of

the

Belgium-Central

and

Eastern

Europe

Research Fellowships Programme of the Bel-
gian Federal Office for Scientific, Technical and
Cultural Affairs.

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Jo Dewulf is post-doctoral researcher at the Ghent University. His
research activities are in the field of environmental chemistry and
technology, with a focus on volatile organic compounds.

Herman Van Langenhove is full professor at the Ghent University.
His research and teaching activities are related to environmental
organic chemistry, including analysis, environmental chemistry and
environmental technology.

Gyula Wittmann is assistant professor at the University of Szeged.
His research and teaching activities are in the field of environ-
mental analytical chemistry and environmental technology.

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