Anal. Chem. 1998, 70, 321R-339R Gas Chromatography Gary A. Eiceman*
Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003
Herbert H. Hill, Jr.
Department of Chemistry, Washington State University, Pullman, Washington 99164
Jorge Gardea-Torresdey
Department of Chemistry, University of Texas, El Paso, El Paso, Texas 79968
Review Contents
themes highlighted in this review, and this was particularly true
with detectors and field instruments. REVIEWS, BOOKS, AND GENERAL INTEREST
Review articles appeared on subjects closely paralleling the
previous format here, including highlights with multidimensional
chromatography and extraction of information from chromato-
graphic data among others. A noteworthy effort was a review of
attempts toward creating unified chromatography, i.e., a single
instrument supporting GC, LC, and SFC methods (A1). The long-
standing interest in chromatography through specific retention
principles was represented by a review of complexation gas
chromatography and molecular recognition in separations (A2).
Significant amounts of research from the former eastern bloc
nations have become conveniently available as translations, typified
Pattern Recognition and Artificial Intelligence
by a review on physiochemical fundamentals of capillary gas
chromatography (A3), where emphasis was given to retention
High-Speed and Portable Gas Chromatography
mechanisms. A third area of advance, that of data extraction from
chromatographic information, was reviewed for artificial intel-
ligence tools (A4) and multivariate mathematical models forevaluation of retention data matrixes (A5).
This review of the fundamental developments in gas chroma-
Multidimensional gas chromatography received substantial
tography (GC) includes articles published from 1996 and 1997
treatment, with reviews reflecting the growing interest in GC-
and an occasional citation prior to 1996. The literature was
GC or liquid chromatography (LC)-GC and the creation of a
reviewed principally using CA Selects for Gas Chromatography from
substantive body of experience and research. A broad argument
Chemical Abstracts Service, and some significant articles from
for multidimensional separations focused on a comprehensive
late 1997 may be missing from the review. In addition, the on-
approach with theory (A6), and others presented reviews with
line SciSearch Database (Institute for Scientific Information)
specific applications to aromas (A7) and environmental samples
capability was used to abstract review articles or books. As with
(A8). A multiple detector alternative to multiple columns was
the prior recent reviews, emphasis has been given to the
identification and discussion of selected developments, rather than
Reviews on chromatography with emphasis on uses directed
a presentation of a comprehensive literature search, now available
toward specific materials were published and are included here
widely through computer-based resources.
since the presentations may provide insights into limitations and
During the last two years, several themes emerged from a
basic challenges in GC. The articles were directed toward
review of the literature. Multidimensional gas chromatography
pheromones (A10), odorants in foods (A11), pesticides (A12), and
has undergone a transformation encompassing a broad range of
activity, including attempts to establish methods using chromato-
Two books published during this review cycle included a
graphic principles rather than a totally empirical approach.
discussion of the theory and practice of headspace sampling with
Another trend noted was a comparatively large effort in chro-
GC (A14) and a GC/MS handbook with little fundamental and
matographic theory through modeling efforts; these presumably
wholly pragmatic importance (A15). The presentation of data in
became resurgent with inexpensive and powerful computing tools.
this handbook reflects the need for continued work in artificial
Finally, an impressive level of activity was noted through the
intelligence in data treatment per section below.
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
SOLID ADSORBENTS AND SUPPORTS
amorphous silicas, because of the possibility of a partial adsorption
Several types of liquid phases have been reported during this
of alkane chains between the layers of this silica.
review cycle and include synthetic organic phases, chiral and
Reports on other natural adsorbents and supports, including
natural phases, inorganic salts, and metal-based phases. As in
alumina, quartz, various types of clays, and cellulose, were given
prior reviews, discussions in this section have been restricted to
during this review period. The diffusion of ethyl methyl ketone,
reports in which solid adsorbents are discussed or characterized
methyl alcohol, and acetaldehyde vapors on alumina was studied
with emphasis on new or modified materials. As in past reviews,
(B21). Carbon-modified aluminum oxide columns were used to
inverse gas chromatography (IGC) was an important method for
separate saturated hydrocarbons (B22). In this report, the
investigating surface structure and interactions between solid
investigators found that the adsorption capacity of adsorbents with
respect to saturated hydrocarbons increases significantly with
Natural Adsorbents.
carbon content. A study on the adsorption of water vapor on
adsorption and chromatographic properties of carbon adsorbents
activated alumina also appeared (B23). This report indicated that
was evaluated (B1). In this study, the arrangement of hexagonal
a molecule of water is bound to two adjacent hydroxyl groups.
layers in the nanostructure of carbonaceous materials was
Others evaluated aluminum oxide-coated porous layer open
determined to help their adsorption and GC properties. The
tubular columns for the analyses of propylene and ethylene (B24).
intramolecular interactions in GC on carbon black coated with
Others studied the adsorption of gaseous chlorides and oxychlo-
monolayers of hydrocarbons with different electronic structures
rides on quartz chromatographic columns (B25).
was also explored (B2), and a series of novel GC graphite-coated
The effect of thermal and chemical treatments on the variation
capillary columns were evaluated by using polarity parameters
of specific surface area of porous bentonite as a support in gas
(B3). A hexafluoropropylene epoxide-coated graphitized carbon
chromatography was studied (B26). These processes changed
black adsorbent was used to determine the retention character-
the surface structure of bare bentonite and contributed to a good
istics of 13 heavier than ethane-based and eight ethene-based
separation of hydrocarbon mixtures. Others modified diatoma-
halocarbon fluids (B4). The relative retention data were fitted to
ceous supports with phenol-formaldehyde, polyoxyalkylene-
linear models for the purpose of predicting retention behavior of
polyurethane, polymethacrylate, and epoxy resins to investigate
these compounds to facilitate chromatographic analysis. Also, a
the possible use of the obtained sorbents in gas chromatography
similar hexafluoropropylene epoxide-modified graphitized carbon
(B27). A method for the deactivation of diatomaceous solid
material was used to determine the Kovats retention indexes of
supports based on the adsorption of polyethyleneimine and cross-
halocarbons (B5). Gas-solid chromatography was used to
linking by a bidentate reagent was also reported (B28). The
determine the Henry’s law gas-solid second virial coefficients
retention ability of different types of solid supports with respect
for hydrocarbons, chlorofluorocarbons, ethers, and sulfur hexaflu-
to active agents was studied using NaX-type zeolites (B29). The
oride with a microporous carbon adsorbent (B6). The thermo-
relative contribution of the zeolite to the overall adsorption of
dynamics of gas adsorption on coal was also studied (B7). Others
certain hydrocarbons was determined. The kinetic parameters
attempted to alter or improve carbon black adsorptivity through
for the ring opening of cyclohexane over modified ZSM-5 zeolites
surface modifications with a high-frequency plasma (B8).
were also studied (B30). The separation of aliphatic alcohols was
Modified GC equations were studied with nonporous silica
successfully performed on a packed column with a support coated
particles packed into fused silica capillary columns (B9), and the
with cellulose tribenzoate, and GC temperature programming
adsorption properties of silica gels with chemically bonded
improved the separation (B31). A report showed the selectivity
aminopropyl and guanidinoethanethiol groups were also investi-
of a saltwater stationary phase for the separation of mono- and
gated (B10). Column packing containing N-benzoylthioureacop-
polyhydroxy isomers on a chromatographic column containing
per(II) complexes chemically bonded to silica supports were used
H2O (B32). In summary, the studies
to study the specific interactions of this modified silica with
suggest a high level of sustained development and discovery of
electron-donor adsorbates such as ketones, ethers, and nitroal-
natural materials to be used for separations in GC methods.
kanes (B11). More recently, the same investigators studied the
Synthetic Adsorbents.
adsorptive properties of silica chemically modified by Cu(II)
utilized to investigate properties of several materials. Reports that
complexes via amino groups (B12). The surface of silica was also
used IGC included the following: the structural characterization
modified using octadecyl (B13, B14), amino, and guanidino groups
of the deactivation of silica surfaces with a silanol-terminated
(B15). A review on molecular statistical modeling and gas
polysiloxane (B33); the examination of acid-base and some other
chromatographic studies of hydrocarbons on modified layered
properties of solid materials (B34, B35); the estimation of surface
silicates and silica in the Henry’s law region was reported (B16).
energy of modified TiO2 pigments (B36); the surface characteriza-
The results of this study can be used to develop new, efficient
tion of cellulose fibers (B37); the determination of the properties
adsorbents and supports based on layered silicates and silica. A
of the films formed by organic substances on a silica gel surface
salt-modified silica gel adsorbent, coated with disodium hydrogen
(B38); the measurement of the surface energies of spherical
phosphide, was also studied (B17). The dispersive and specific
cellulose beads (B39); the determination of the chemical and
adsorption energies of alkanes (B18) and benzene on silica gel
morphological characteristics of inorganic sorbents with respect
were also studied (B19). Other types of silicas, amorphous silicas
to gas adsorption (B40); the characterization of the cork surface
and crystalline silicic acid, were evaluated for their alkane
(B41); the determination of intermolecular interactions for hy-
adsorption energies (B20). The value of the surface energy of
drocarbons on Wyodak coal (B42); the assessment of the surface
the crystalline silicic acid was found to be higher than that of the
energies of theophylline and caffeine (B43); the estimation of the
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
thermodynamics of adsorption of n-alkanes on maleated wood
nematic, smectic, cholesteric, low-molecular, high-molecular,
fibers (B44); the investigation of surface properties of protective
crown ether, and macromolecular crown ether liquid crystals).
coatings of optical fibers (B45); the study of the physicochemical
Several GC stationary phases containing crown ethers were
properties of polypyrrole-silica nanocomposites (B46); and the
reported (C10-C12). Two new chiral polysiloxanes containing
determination of the surface properties of illites and kaolinites
crown ethers were prepared for capillary GC (C10). Others
(B47). In addition, surface adsorption isotherms, solubility
parameters, thermodynamic interactions, and glass transitions
C6 carboxylic acids when using benzo-15-crown-5 as
were all characterized using IGC for several new polymeric
stationary phase (C11). A new calixcrown polysiloxane GC
materials (B48-B62). Other studies showed the adsorption and
stationary phase was synthesized (C12). This phase, in which
gas chromatographic properties of microspherical hyper-cross-
the calixcrown monomers lie in the main chain of polysiloxane,
linked polystyrene sorbents (B63). The highest retentions for
showed good separation properties for nitro-, chloro-, and methyl-
various types of organic compounds were observed on polymer
substituted benzene or phenol isomers. Other new developments
microspheres with the highest degrees of cross-linking. In
with liquid phases were made with more traditional polymers, such
another report (B64), the adsorption properties of the porous
as dicyanobiphenyl polysiloxane stationary phases (C13). Others
polymers Porapak R and Porapak T were studied. Others studied
evaluated chemically bonded squalene phases for the separation
the adsorption of various organic compounds, including alkanes,
of hydrocarbons (C14, C15). Also, the effect of the dioxa[11]-
aromatic hydrocarbons, aldehydes, ketones, and esters, on Porolas
paracyclophane group in polysiloxane stationary phases was
polymers (B65). The vinyl chloride adsorption properties of the
examined (C16). The incorporation of n-alkyl groups on cyclic
polymer poly(vinyl chloride) were also studied (B66). Others
siloxane bonded phases was also studied (C17). The incorpora-
reported the structure and gas chromatographic properties of new
tion of octyl and octadecyl groups on the siloxane skeleton greatly
sorbents prepared by the radiation-stimulated polymerization of
improved the retention capacity for light hydrocarbons. This
2-butyne-1,4-diol, 2,4-hexadienoic acid, and 1,2,3-propenetricar-
behavior was due to the high surface coverage of the packing
boxylic acid on the surface of polysorb-1, a styrene-divinylben-
material and, thus, to a better solute-stationary phase interaction.
zene copolymer (B67). The retention properties of 15 hydrocar-
In addition, the effect of alkylbenzene groups (C18), N-alkylimi-
bons on a new GC stationary phase, poly(perfluoroalkyl ether),
dazole groups (C19), and phenyl groups (C20) in polysiloxane
were also reported (B68). The hydrocarbon-perfluoro compound
stationary phases was investigated. Others examined the pos-
interactions showed pronounced positive deviations from the ideal
sibility of using three polar-type liquids containing (methyl)oxy-
behavior and can be attributed to repulsions between the
alkane, cyanoalkane, and alkanethiol groups as GC stationary
hydrocarbon and the perfluorocompound segment. In another
phases (C21). Chemically bonded cyclic organosiloxanes-silica
work (B69), quantitative structure-retention relations in GSC
gels were evaluated (C22) for possible use in microcolumn GC
were employed as a method to study the inclusion properties of
of light hydrocarbons. Two reports appeared on the use of
the p-tert-butylcalix[4]arene phase in a micropacked column.
dicumyl peroxide for the cross-linking of GC stationary phases
Synthetic inorganic materials were the subject of one study that
(C23, C24). Two related studies (C25, C26) showed the variation
reported the use of thorium bis(monodecyl phosphate) as a GC
of selectivity among many polysiloxane stationary phases for GC.
The selectivity differences were explained in terms of differencesin the cohesive energy of the solvents and their capacities for
LIQUID PHASES
dispersion, dipole-type hydrogen bonding, and electron pair
Synthetic Organic Phases.
complexation interactions. These reports concluded by speculat-
liquid GC stationary phases ranging from squalane (retention
ing on the needs for new phases to explore the full selectivity
polarity ) 0) to bis(cyanoethoxy)formamide (retention polarity
potential in GC. Others evaluated resorcarene derivatives for the
) 144.6) was reported (C1). Several liquid crystals were studied
separation of substituted benzenes (C27), and 1(R)-trans-N,N′-
as possible stationary phases in GC. The separation properties
1,2-cyclohexylenebisbenzamide for the separation of L-2-hydroxy-
of hydrocarbons were examined with AVIK-85 (a tetrahydroxy-
glutaric acid in urine (C28).
quinone derivative) on Chromosob-W and Silochrom C-80 sup-
Chiral Phases and Natural Phases.
ports (C2). The same AVIK-85 liquid crystal was evaluated
review, the most prevalent phases in this section were based on
through various cycles of heating and cooling of a chromato-
cyclodextrin and cyclodextrin derivatives (C29-C64). Cyclodex-
graphic column (C3). Other liquid crystal phases were evaluated
trin and modified cyclodextrin stationary phases were used for
for the separation of 2,3,7,8-substituted chlorinated dioxin isomers
the separation of stereoisomers of 3,4-diphenylcyclopentene (C29),
in capillary columns (C4), the separation of isomeric phthalic acids
methyl 2-chloropropionate (C30), volatile compounds in oils
(C5), and selectivity for polycyclic and aromatic compounds (C6).
(C31-C33), PCBs (C34), organophosphorus chemical warfare
Others compared two azobenzene liquid crystal stationary phases
agents (C35), xylenes (C36), fatty acid methyl esters (C37),
in open tubular column GC for the isomeric separation of various
furanoids (C38), aromatic alcohols (C39), di- and trisubstituted
types of organic compounds (C7). The separation of positional
benzene (C40, C41), methyl and phenols (C42), R-campholene
isomers of aliphatic, aromatic, and polyaromatic hydrocarbons of
and fencholene derivatives (C43), amino alcohols (C44), and DDT
three laterally substituted liquid crystal stationary phases was also
(C45). The mechanisms of separation of cyclodextrin and
reported (C8). A review with 101 references on the development
modified cyclodextrin stationary phases are based on van der
of liquid crystals as stationary phases in GC was given (C9). This
Waals forces (C46), hydrogen bonding (C47, C48), sizes of the
review includes the classification of liquid crystals for GC (e.g.,
inclusion cavity (C49-C51), polar interactions (C52-C54), and
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
steric interactions (C55). Others found a synergistic effect when
Table 1. Examples of Physicochemical
cyclodextrin stationary phases were mixed with resorcarene
Parameters for Solution Studies Using Gas
(C56), and the necessity of an aromatic system for enantioselective
Chromatography
phases was determined (C57). In addition, cyclodextrin and
adsorption coefficients with improved equation for
modified cyclodextrin stationary phases were examined to deter-
partition coefficients of benzenes and essental oils
mine the contribution of thermodynamic parameters to chiral
activity coefficients with interfacial adsorption
C58-C60), the influence of diluting the phases on
Gibbs energies of solution and molecular structures
enantioselectivity (C61-C63), and the influence of structural
donor-acceptor associations with enthalpy measurements
characteristics on chiral selectivity (C64).
thermodynamic parameters for solubility with
The adsorption properties of a GC glucose-modified silica
surface were reported (C65). The additional glucose modification
London dispersive component of the surface free energy
activity coefficients and Flory-Huggins interaction parameter
increased the adsorption potential for molecules with polar
partial molar enthalpies of mixing at infinite dilution
functional groups. The resolution of enantiomers of various
compounds was evaluated using L-valine-tert-butylamide (C66,
C67), chirasil-Val (C68, C69), L-tert-leucine-tert-butylamide (C70),and tripeptide derivatives (C71).
Other retention models were described and were useful in
Inorganic Salts and Metal-Based Phases. The chromato-
restricted models for prediction, such as the use of number of
graphic properties of stearyl-1-R-naphthyl acetate were examined
chlorines in predicting PCB retention (D13). Others have used
as a GC stationary phase (C72). This phase falls in the medium
carbon numbers in alkyl chains (D14), boiling points (D15),
polar category and can be a versatile, easily available phase for
enthalpy (D16), and combinations of these (D17). On the whole,
GC. A GC stationary phase containing chiral chelates of europium
these attempts are directed at fairly narrow variations on structure
was found to exhibit high selectivity for nucleophilic solutes (C73).
and will be useful for targeted understandings. In contrast, the
Successful enantiomeric separation of selected alcohols and
works referenced in the previous paragraph have universal
ketones was obtained. However, no separation of chiral com-
pounds containing double bonds and chloro aliphatic compounds
Predictions on the role of temperature on retention dates from
was observed. Others evaluated copper(II) chelates of tetraden-
before the inception of temperature programming, though oven
tate -ketomaines as GC stationary phases (C74). These phases
programming has elevated the importance on linking retentions
showed a high potential for the separation of alcohols, ketones,
from isothermal and programmed temperature experiments. This
and heteroaromatic compounds. The complexing GC stationary
has reached an advanced stage of refinement, and some have
phases containing tris[3-((trifluoromethyl)hydroxymethylene)cam-
reported differences of below 1% between predicted and measured
phorato]-derivatives of lanthanides were also characterized (C75).
retention times (D18-D20). A flexible model, in which temper-
In another report (C76), IGC was used to determine the solubility
ature plateaus are allowed, showed errors of 4% on retention and
and polarity parameters for pyridinecarboxamides and their
10% on peak widths (D21). An attempt to minimize the number
of experiments for such accomplishments was described (D22),and one model included a detailed consideration of column
CHROMATOGRAPHIC THEORY
The major themes for this section are based on studies where
General retention within gas chromatography underwent
chromatographic behavior is associated with the molecular
significant advances during the last two years, with noteworthy
structure of solute or stationary phase and the connections
advances in a unified retention concept (D24), in a universal
between thermodynamic parameters on efficiency, resolution, or
database (D25), and in classification of stationary phases using
Kovats coefficients (D26, D27). These works have a common
Structure-Retention Studies.
aim, which is to free investigators from the inconvenience of
noted in this subject, with over 73 articles on a main premise:
empirical determinations of retention when various stationary
Can retention times be predicted from molecular structure? Three
phases are employed. While developments toward this goal
descriptors or guides for linking structure to retention have
seemed promising (D26), interfacial adsorption for polar phases
emerged: topologic, geometric, and electronic terms (D1-D4).
was recognized as a variable which cannot be ignored (D25) and
In general, these tools are still in a semiempirical state of
may defeat wishes for a highly refined and broadly applicable set
development, where the models are being developed through
correlations between retention indexes and molecular details. In
Thermodynamic Parameters.
other models, molar volume and solubility parameters have
solvent interactions has been a mainstay in gas chromatography
formed the basis of correlations (D5). Still others have used
for decades, and this area saw active development, even in 1996-
selected descriptors, including topologic (D6), electronic interac-
1997. Since the studies are often very specific and only together
tions (D7), conformations (D8), and van der Waals volumes (D9).
comprise significant importance for GC, the results are sum-
In these, molar volumes appear to be an influential descriptor
marized in Table 1. The listing demonstrates that GC has been
(D10, D11), except where gas solid chromatography was involved
maintained as a research tool for gleaning constants and physical
terms for molecular events or properties.
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
to correlate GC equations with thermodynamic parameters (E16)
Table 2. Studies for Various GC Parameters
and to determine the adsorption mechanism of n-alkane retention
with various liquid stationary phases (E17). Also, a super long
mathematical model for asymmetry in peak shape
modeling molecular basis for separation of enantiomers
equilibrium-dispersive model for elution band profiles
for the separation of gasoline (E18). The column had 1.3 million
model for separations of multiple phases such as GC-GC
effective plates and was built up by connecting nine 50-m columns
assessment of corrected retention volumes in GC
dependence of retention on carrier gas pressure in GSC
in series. This new column resolved up to 970 components in a
specific retention volumes for capillary GC with ∼1% error
specific retention volumes calculated from retention indexes
dimensional packed-capillary column was reported (E19). In the
new polarity scales for phases using Kovats coefficients
two-dimensional system, the column efficiency was determined
discovery of failure with variance additivity in
by the solute’s retention time and the ratio of peak spreading in
void volume and mobile phase volume measured
the precolumn and the main column. It was concluded that, in
model for flow control in temperature programmed GC
order to improve column efficiency, matching of the precolumn
influence of coating thickness and temperature on dead time
and main column conditions was necessary. Others reported (for
comparison of dead time methods: Grobler-Balizs
the first time) the chemical modification of open tubular columns
moving focusing in chromatographic resolution
with a functionally selective immobilized stationary phase (E20). The column modification was performed by the oxidation of the
A general category of miscellaneous facets with the theory of
polyol polymer with nitric acid. The optimization of temperature-
gas chromatography showed a remarkable degree of diversity and
programmed GC separations using off-line simplex optimization
level of activity. In some works, resolution and peak shape were
and column selection was studied (E21). This study indicated
the main considerations while in others, influences on retention
that fully off-line simulation and optimization of single ramp and
were explored; still others addressed what are often neglected
multiramp temperature-programmed GC separations as well as
issues in GC, such as dead time and void volume. These are listed
column selection was possible. A subambient GC temperature
in Table 2 and suggest a broad range of study in this domain of
programming method using two isothermal gas chromatographs
was also reported (E22). Another report in this area was thedevelopment of a thermal desorption modulator for GC (E23). In
COLUMNS AND COLUMN TECHNOLOGY
addition, automatic thermal desorption in GC was used for the
The major themes of this section are new developments and
analysis of volatile food components (E24, E25). A new GasPro
improvements in column designs as well as new attempts at
GC PLOT column for the separation of gases and highly volatile
creating columns for evaluation of chromatographic principles or
for enhanced selectivity. A review with 11 references appeared
on the use of metal capillary GC columns as an alternative to fused
between the GasPro column and a conventional doped aluminum
silica columns (E1). A new wall-coated open tubular metal column
oxide capillary column. The GasPro column was not adversely
was developed for the separation of petroleum-derived waxes and
affected by water, carbon dioxide, and sulfur gases, and it appeared
high-molecular-mass linear alcohols and acids (E2). Others made
to be more inert than the aluminum oxide column, since it did
new inert stainless steel capillary columns by a multigradient layer
not cause decomposition of most reactive analytes. Also, a new
technology (E3). Also, a new deactivated metal capillary GC
type of quartz-lined aluminum capillary GC column coated with
column was used for the determination of trace amounts of
graphitized carbon black was prepared (E27). This new column
triazolam in serum (E4). This metal column exhibited excellent
was resistant to drastic acidic or alkaline treatments, and it was
thermostability at high temperatures. Several new GC porous
evaluated for the analysis of amines, VOCs, and oil products.
layer open tubular (PLOT) columns were also reported (E5-E10).
Others reported a new type of high-performance submicroparticle
Some characteristics of these new PLOT columns included the
packed column (E28). This column was found to have properties
in situ polymerization of the monomer (E5, E6), a new method
similar to those of capillary columns for the analysis of high-
of silica modification (E7), a less reactive column which is
boiling-point compounds at relatively low column temperatures.
sufficiently inert to separate volatile chlorofluorocarbons (E8), a
A packed glass capillary column with multicores was also prepared
charcoal-based column capable of resolving light hydrocarbons
and was shown to have a better permeability than conventional
(E9), and an ultrafine zeolite-based column with high speed and
packed capillary columns (E29). In addition, a GC capillary
selectivity (E10). Others also reported the preparation of a zeolite
column which can be directly heated by an internal chromium/
membrane PLOT column by in situ synthesis (E11). A new type
nickel wire was developed (E30). The separation of C -
of SCOT column with ultrafine zeolite was also described (E12).
hydrocarbons was demonstrated with this column, and it was
The ultrafine zeolite had a fine and uniform particle size, large
compared to conventional column oven heating. High-tempera-
specific surface area, regular crystal structure, and similar chemi-
ture GC capillary columns, which can be used up to 360 °C, were
cal constitution to glass. Two new methods for the preparation
prepared and characterized (E31). Others developed a new type
of microcolumns were also evaluated (E13, E14). These columns
of strongly polar organic polymer PLOT column by in situ
contained cross-linked, bonded polysiloxane stationary phases of
copolymerization of acrylonitrile and divinylbenzene (E32). Also,
well-defined thickness (E13) and (aminopropylsilyl)dithiooxamide
a way of controlling the maximum allowable oven temperature
bonded phases (E14). The use of a short microcapillary GC
during on-column injection by the column pressure drop was
column (i.d. ) 50 µm) for rapid triglyceride analysis in fats and
suggested (E33). In this report, an arrangement using a restrictor
oils was reported (E15). Open tubular GC columns were used
at the column outlet for adjustment of the column inlet pressure
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
was evaluated. The polarity and adsorptivity of nondeactivated
carbons in edible oils (F18). In another article, the conditions of
GC capillary surfaces were tested (E34). The effect of various
sampling the first column were explored relevant to recovery of
leaching and etching procedures used for column preparation,
reference standards in determination of polychlorinated biphenyls
as well as the stability of uncoated fused silica precolumns toward
(F19). Finally, the linearity and precision for LC-GC were
water and some organic solvents, was studied in this report.
documented using phyrethorid insecticides in fruit extracts (F20). Recoveries were good, and reproducibility was high (0.6-6.6%). MULTIDIMENSIONAL GAS CHROMATOGRAPHY
The growing trend in multidimensional gas chromatography
DATA PROCESSING AND QUANTITATIVE
was distinguished during this review cycle by advances in the
subject of modeling and optimizing two-dimensional gas chroma-
Previously, data processing was regarded as a means to provide
tography and by a dramatic increase in liquid chromatography
insights into chromatographic events, and the efforts were limited
(LC)-GC techniques. Applications continued to lead in all
in scope. During this last review cycle, a remarkable surge
reports, as true throughout gas chromatography literature every-
occurred in reports on data processing. This occurred in both
where, though the foundations of a systematic methodology are
the scope and the number of studies. The causes for this vitalityand diversity are unknown but might be attributed to the
being explored, fortunately. Automation and hardware were minor
availability of powerful and affordable computers.
themes, in contrast to reports from the past decade. Optimization and Simulations. Optimizations and simula-
Models and optimization constitute an encouraging develop-
tions represented a significant portion of work in this section and
ment in multidimensional gas chromatography, since, without
included an examination of signal processing, such as the
foundational tools for designing methods or interpreting results,
performance of digital processing for selected ion monitoring (G1).
the subject will remain in a highly empirical condition. The article
Computer modeling was used for optimizing column parameters
that best represents this involved modeling retention and separa-
via commercial software (G2) and through neural networks (G3).
tions in three capillary columns (F1). In three other articles, a
Selectivity in GC was optimized and verified experimentally
main theme was optimization of selectivity in two-dimensional GC
through simplex methods, enhanced through the use of a
(F2-F4). These articles are not directly available in English and
polynomial gleaned from preliminary measurements (G4).
are noted for their importance in the development of multidimen-
Advances in comparison of retentions were made using
sional gas chromatography. Elsewhere, attempts to maximize 2-D
thermodynamic retention indexes (G5) and used with simulations
GC were made by exploiting thermal modulation for complete
to explore separations by GC (G6). Predictions of numbers of
characterization of every peak eluting from the first column (F5,
components were accomplished via a statistical model of overlap
(G7). The high level of current capabilities in the overlap between
A remarkable activity in the coupling of LC with GC has
computation and separations is illustrated by simulations of
occurred, despite a first impression of apparent incompatibility
retention for highly complex mixtures (G8) and for simultaneous
in strengths of LC for large nonvolatile molecules. However, in
programming of temperature and column head pressure (G9).
nearly all reports for LC-GC, the liquid chromatograph was used
Pattern Recognition and Artificial Intelligence. As in past
principally for prefractionation of a complex mixture to isolate a
activity within this section, multivariate data analysis has been
targeted GC-compatible substance. Examples include polycylic
used powerfully with complex mixtures, suggesting that tools
aromatic hydrocarbons (F7, F8), alcohols and sterols (F9),
exists for coping with the large information density presented by
morphine and analogues (F10), PCBs and pesticides (F11),
-blocker (F12), and thiols and other sulfur-containing compounds
become an element of foundational significance in handling
(F13). Though these are application-driven reports, they are noted
chromatographic data, extending and expanding the meaning of
here to document the activity in one future direction for multidi-
chromatographic resolution. Also, as in the past, the best
mensional gas chromatography and the relevant basic research
examples come from complex natural or environmental samples.
These have included blueberries (G10), orange juice (G11),
A persistent subject in multidimensional gas chromatography
microbial defects in milk (G12, G13) and fresh cabbage (G14)
has been the hardware to combine multiple columns without
for foods. Neural networks were found to correlate sensory
degradation in peak shape and automation of instrumentation. This
evaluation with chromatographic headspace analysis with good
was a weakly active area in the last review cycle and is best typified
success (G15). Complex processes of weathering for a complex
by interest in valve connections or traps between columns in GC-
sample, jet fuel, were successfully modeled and linked to dis-
GC (F14, F15) and LC-GC (F16). A noteworthy variation from
criminant functions, demonstrating the advanced role of artificial
linearly coupled columns is that of parallel columns, after a
intelligence methods with chromatography (G16). Similar success
precolumn, with a single detector (F17). In this work, retention
was obtained with plastic-bonded explosives (G17). These routes
behavior was modeled and was 0.3-0.6% of predictions.
to data processing are sufficiently mature to become common tools
Enhancements in confidence or specificity of detection via
resolution with two stationary phases was and remains a motiva-
An ancillary challenge to handling complex data sets for refined
tion for multidimensional gas chromatography. Consequently, the
understanding of total composition or sources assignment is the
literature in this subject is weighted toward applications, as is true
extraction of specific information from simple or complex chro-
in all of gas chromatography. A few articles illustrate a mixture
matographic data. Information theory and calibration standards
of application and critical evaluation, such as the comparison of
were used to establish chromatographic performance (G18), and
LC-GC versus the official analytical method for steroidal hydro-
throughput increases were controlled with an expert system
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
(G19). Chromatographic separation was also established using
of analysis were obtained for a series of pesticides (H16).
simplified Fourier analyses, with additional benefits of disclosing
Multidimensional HSGC showed low-capacity factor compound
overloading effects (G20). Extraction of information from GC/
separations (H17) with many possible applications (H18). Two
MS screenings was accomplished automatically with low S/N
columns with opposite stationary phases (polar and nonpolar) were
levels (G21) and through differential results (G22). The automa-
optimized by adjusting the midpoint pressure to attain maximum
tion of retention index comparison attracted some effort, including
resolution for a critical pair (H19).
a merging of isothermal and programmed data sets (G23) and
Injection techniques for HSGC must provide narrow band-
the use of diverse literature sources (G24). Such advances will
widths due to fast analysis time requirements without compro-
be necessary for full exploitation of chromatographic data in
mises in resolution (H20). Cryogenic inlets were the most popular
chemical identifications, as typified by a new software program
method of introduction. Two cryofocusing inlets provided band-
widths between 5 and 10 ms (H21). A cryogenically controlled
Quantitative Aspects. The subject of quantitative determi-
microloop gave bandwidths of <10 ms (H22) and was compared
nations by GC received small but refined examinations during
with a capacitance-heated metal cryotrap in a recent study (H23).
this review cycle. For example, the influence of matrixes on
A cryotrap/thermal desorption inlet with 10 different deactivated
pesticide determinations was addressed (G26). Matrixes can
tubes was evaluated and found to provide minimal thermal
reduce losses of pesticides on surfaces, and matrix standard
decomposition in 6 of the 10 tubes (H24).
calibration solutions were described. In another work, the signal
As with injectors, compatible detectors for HSGC must be fast
associated with a chromatographic blank was obtained through
enough to resolve narrow peaks, which requires minimal dead
use of background noise, suited to further statistical evaluation
volume and fast electronics (H25). When a mass spectrometer
(G27). The determination of morphine in opium using complex
is coupled to HSGC (H26), fast scanning rates are necessary, and
pyrolysate chromatograms was advanced using principle compo-
scanning rate limits of >25 000 amu/s have been shown when a
nent analysis and provided quantitative results (G28). Quantitative
quadrupole mass filter was implemented (H27). Utilizing a fast
determinations with gas chromatography-mass spectrometry
double-focusing mass spectrometer showed improvements in both
were also explored and characterized for variance from various
detection limits and interferences (H28).
steps of an entire method for cholesterol. Not surprisingly, sample
One tradeoff for HSGC is the loss of capacity due to the smaller
collection and preparation contributed the bulk of variance, and
diameter and shorter columns. Application of packed capillary
the instrumental determination was less than 30% of the total
columns in HSGC has been shown to improve capacity and
(G29). Methods for testing scanning mass spectrometry for
selectivity (H29) while obtaining high-speed separation for light
linearity of response were presented (G30), and minimum detec-
hydrocarbons (H30). By implementing supercritical fluid/gas
tion limits were approached using principal component analysis
chromatography conditions along the column, less volatile com-
pounds can also be separated by using packed capillary columns(H31). A multicapillary column improved capacity while maintain-
HIGH-SPEED AND PORTABLE GAS
ing the efficiency obtained with small internal diameter columns
CHROMATOGRAPHY
In recent years, the need for rapid and portable analytical
measurements has led to the development of gas chromatographs
Many portable HSGC instruments are being used for on-site
with fast separation times and small instrumentation (H1). Several
analysis (H33). A micro-GC coupled with a thermal conductivity
recent reviews examined the techniques for increasing analysis
detector (TCD) was shown to separate CO2 and C1 C6 alkanes
times in GC, such as using short narrow-bore columns (H2, H3)
within 30 s. Petroleum industry application included detection
and optimizing the mobile phase parameters (H4). Theoretical
of H2S and COS impurities (H34) and rapid screening for gasoline
expressions for typical high-speed gas chromatography (HSGC)
to diesel range organic compounds (H35). Environmental prob-
conditions have been derived and compared with the Van Deemter
lems are a major application for portable GC systems due to the
equation (H5). Differences were found due to the higher pressure
complexity of the samples (H36). Recent separations in this area
drop across the column for HSGC. Conventional GC instruments
include separation of multiple pesticide residues in agricultural
have been reviewed for compatibility with HSGC conditions (H6),
products (H36), air analysis (H37), and the detection of polychlo-
and one major problem discovered was due to slow data acquisi-
rinated biphenyls (PCBs) (H38). Other applications which have
tion rates and large amplifier constants (H7).
recently been tested with HSGC involve leak verification (H39),
New commercial HSGC systems have been presented which
identification of pesticides in plasma samples (H40), and separa-
utilize smaller thermal ovens (H8) and innovative column heating
tion of thermally labile steroids, carbamates, and drugs (H41).
arrangements (H9). Column heaters based on resistive heating
Because gas chromatographic instruments can be made light
were shown to be compact, utilize minimal power, and decrease
and energy efficiency, considerable emphasis over the past two
sample analysis times (H10). Resistive-heating combined with
years has been placed on developing portable gas chromatographs
temperature gradients along one column (H11) resolved 13
for the separation and detection of target compounds in the field
compounds with baseline separation in 3.5 s (H12) and was shown
(H42). Gas chromatographs have been developed which are truly
to be compatible with the addition of a second column (H13).
portable, with approximately 100 W of power at peak-to-peak power
Dual-column HSGC has been investigated for both the theoretical
consumption (H43). More importantly, small GCs are not limited
possibilities (H14) and its applications (H15). Two-column
to operation in the field. In the laboratory, they have the
separations with high-resolution mass spectrometry (HRMS),
advantages of operation with minimal consumption of utilities such
improved sensitivity, short analysis times, and decreased costs
as compressed gases, electricity, space, and so forth.
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
The primary focus of research and development in field gas
instrumental control methods have been developed for more
chromatography (FGC) during the past two years has been
precise control of the operating temperatures and gas flow rates
instrument miniaturization. The ultimate miniature FGC system
(H61, H62). One approach for improved injection technologies
was designed and developed using Si micromachining and
is called thermal modulation (H63). Thermal modulation was
integrated circuit processing techniques (H44). The chromato-
produced from the rotation of a heater element over a capillary
graph consisted of a 10-µm-long sampling loop, a 0.9-m rectangular-
column. This rotation accumulated the analyte and then focused
shaped column, and an injection loop and column each with a
it into a sharp concentrated pulse, injecting the pulse onto the
width of 300 µm and height of 10 µm. The column was coated
GC column. Because the modulation was produced from a
with a 0.2-µm thickness of Cu phthalocyanine as the stationary
controlled rotation of the heater module, repetitive and reproduc-
phase. Detection was based on a dual detection scheme using a
ible sample injections were possible.
coated chemiresistor and thermal conductivity detection. The
One major problem of FGC when compared to laboratory-
complete FGC system was packaged in less than 23 cm2 and was
based instrumentation is the reduced resolution that most field
2.5 mm high. Although limited in scope to the detection of
instruments exhibit. This reduced resolution is compensated for,
ammonia and nitrogen dioxide, this miniature chromatograph
in part, by the use of selective detectors. Detectors such as the
offers exciting possibilities for future field instruments.
electron capture detector (H48), the photoionization detector
One of the more novel approaches reported for FGC during
(H47, H64), and a miniature dual flame photometric detector for
the review period was the miniaturization of a tandem GC
phosphorus and sulfur compounds (H57) have all been interfaced
instrument (H45). This potential field-portable GC-GC method
of separation involved dynamic coupling between two short
The most versatile selective detector for GC is the ion mobility
capillary columns. Each column could be independently optimized
spectrometer or detector; recently, it, too, has been coupled to
with regard to temperature and flow rate. Dynamic coupling was
gas chromatographs for field analysis (H65, H66). A new hand-
accomplished by automated vapor sampling (AVS) techniques.
portable GC/ion mobility spectrometer has been constructed and
Thus, a slowly eluting GC peak from the first column can be
named the EVM II (environmental vapor monitor). The unique
rapidly sampled into the second column, providing a two-
feature of this instrument was the GC column-to-source interface,
dimensional separation of complex samples. The feasibility of this
in which a transfer line was used as the chromatographic column.
tandem GC approach was demonstrated by two-dimensional
The concept has led to the term transfer line gas chromatography
C6 ketones. Other miniature FGC systems have
(TLGC). The utility of this hand-held GC ion mobility detector
also been reported (H46, H47). A detachable column cartridge
instrument was demonstrated by the separation and detection of
was developed which permitted the substitution of columns in
chemical warfare agents such as DMMP within 20 s (H67). One
interesting application of GC/ion mobility spectrometry was for
The most common uses for field gas chromatography (FGC)
the determination of fish freshness (H68, H69). The presence
have been in the determination of volatile and semivolatile organic
of 1,5-diaminopentane (cadaverine) was detected after 4 days,
compounds in the atmosphere. Target compounds for on-site
indicating the on-set of fish decay. Coupling an automated vapor
screening by FGC include benzene in complex environments at
sampler with a transfer line gas chromatograph (AVS-TLGC) and
the ppm level (H49), dimethyl sulfide (DMS) and carbon disulfide
an extremely small ion mobility spectrometry detection device (15
(CS2) (H50), and polychlorinated biphenyl (H51). Indoor air
in.3), an attempt was made to construct a personal chemical hazard
pollutants such toluene, R-pinene, and 1,4-dichlorobezene were
determined, with detection limits in the low microgram per cubicmeter level (
Mass spectrometry is a mature technology and, perhaps, the
H52), and long-lived species were identified in the
upper troposphere and lower stratosphere (H53). Methylphos-
ultimate GC detector, but due to size, vacuum, and energy
phonic acid esters were detected at the 5 ppb level in air (H54).
requirements, it has been limited as a field method. Nonetheless,
Other volatile organics compounds (VOCs) in the atmosphere
considerable attention has been paid to the development of this
(H55) were targeted, as well as soil gases containing BTEX and
technique due to the tremendous benefits that field portable gas
chlorinated solvents (H56). Chemicals for chemical weapons
chromatography/mass spectrometry would provide. One portable
convention treaty verification (H57) and explosives in air from a
GC/mass spectrometer was contained in a standard size suitcase,
walk-through sampling module which provides automatic screen-
weighed about 70 lbs, and required about 600 W of energy for
ing of humans at rates of 10/min (H58) have been screened by
operation under peak load conditions (H71). Such a portable GC/
FGC. These chemicals encompass a wide range of vapor pressure
MS system can be transported to a clandestine laboratory for the
on-site identification of illicit drugs and other related compounds
Problems associated with FGC have included the fluctuation
(H72). A “roving” GC/MS, mounted on a golf cart, was capable
of retention times and the nonreproducibility of injections.
of analyzing up to 1000 samples/h while traveling at a speed of
Humidity may also affect the results of analyses (H59). In general,
20 mi/h (H73). Portable GC/MS instruments were also used for
however, understanding the difference between field screening
industrial hygiene applications (H74). The primary advantage of
and field analysis can reduce the problems associated with field
portable GC/MS instruments is the large number of applications
measurement (H60). By adjusting the data quality requirements
for with this method is useful. As the need for field measurements
with the time requirements, optimal parametric conditions can
increases and mass spectrometry becomes miniaturized, the
be selected in which reliable on-site data can be obtained. In
number of field portable GC/MS systems can be expected to
efforts to minimize problems associated with field GCs, several
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
GAS CHROMATOGRAPHIC DETECTORS
in water (I15). A new type of HID based on dc plasma ionization
In addition to high resolution and speed, gas chromatography
was reported for use with GC (I16, I17) and applied to the
offers the considerable advantage of interfacing with a wide variety
measurements of flammable gases in coal gas (I18).
of detection methods. The myriad of detectors available for gas
(c) Nitrogen-Phosphorus Detector (NPD). The most
chromatography can be separated into two primary categories:
common GC detector based on the ionization of the analyte in
ionization detectors and optical detectors.
the presence of a heated alkali source is the nitrogen-phosphorus
Ambient Pressure Ionization Detectors. Ionization detec-
detector. Developed to maturity, this detector was used in a
tors remain the most common devices used to measure analytes
number of novel applications. Quantification of the metabolite
separated by gas chromatography. Although these methods are
dichloroethylcyclophosphamide was preformed after direct capil-
reaching a mature state of development, considerable research
lary gas chromatography without prior derivatization, with a
activity still exists. Research and development on the following
detection limit of 1 ng/mL (I19). Other applications to biological
ionization detectors have been reported in the literature during
matrixes included determination of yohimbine in commercial
the past two years (listed in order of presentation): the flame
yohimbe products, study of a dietary supplement alternative to
ionization detector (FID), the helium ionization detector (HID),
anabolic steroids (I20), nitrate analysis in biological fluids, in
the nitrogen-phosphorus detector (NPD), the electron capture
which nitrobenzene was produced from the dissolved nitrate (I21),
detector (ECD), the surface ionization detector (SID), the pho-
cyclophosphamide metabolites (I22), simultaneous quantification
toionization detector (PID), the ion mobility detector (IMD), and
of two antidepressant drugs, fluoxetine and desipramine (I23),
and quantification of clozapine (I24) and zolpidem and zopiclone
(a) Flame Ionization Detector (FID). The detector work-
(I25) in human plasma or serum. The NPD was also applied to
horse for gas chromatography remains the carbon-selective flame
food analysis for the determination of fungicide residues in
ionization detector. Several new applications for this detector were
cucumbers (I26), herbicides in drinking water (I27), and imazalil
reported. They included the determination of castor oil fatty acid
residues in lemons (I28). An important environmental application
composition (I1), an Empore disk elution method coupled with
of the NPD was the determination of underivatized nitrophenols
injection port derivatization for the quantitative determination of
in groundwater (I29). Simultaneous determination of 15 organo-
linear alkyl benzenesulfonates (I2), the determination of parac-
nitrogen pesticides was accomplished with a flame thermionic
etamol and dicyclomine hydrochloride (I3), and dual-column
detector (I30). Also, online determination of organophosphorus
hydrocarbon analysis (I4). Related to these routine applications
pesticides in water by solid-phase microextraction techniques was
was a simple and efficient method for the determination of
reported (I31). One approach was investigated for the selective
retention parameters using a methane marker device (I5).
detection of oxygenated volatile organic compounds (I32).
Developmental advances in FID included several modifications
In one, more fundamental study, severe tailing of phosphorus
in design. A compact and low-fuel FID was developed for portable
pesticides was found to be associated with the thermionic
GCs (I6). Fuel flow rates were as low as 12-15 mL/min, and
ionization source and not the column (I33). A novel type of alkali
oxidant flow rates were in the range of 120-150 mL/min. Another
source was reported in which the alkali salt was continuously
improvement to FIDs was reportedly made by the incorporation
introduced into the detector as a solution in water by means of a
of a precombustion chamber to mix the fuel and sample gas (I7).
liquid chromatographic pump (I34). This design had the advan-
Similarly, a premixed FID was developed by adding hydrogen and
tage of continuous refreshment of the source. Also, an alkali flame
air at the same flow rate to the outlet of the capillary column (I8,
ionization detector (AFID) was reported in which an alkali chip
I9). Both hydrogen and oxygen were produced by an electrolyzer
was mounted on top of the collecting electrode (I35) or the
that was incorporated into an FID design (I10). This electrolyzer
temperature of the alkali source could be varied (I36). Flame-
flame ionization detector (EFID) was similar to a standard FID,
free ionization detectors were reported which used a heated
except that the flame tip had a narrower bore to prevent flame
ionization tube of high-purity alumina (I37, I38).
flashback and the entire detector structure needed to be main-
(d) Electron Capture Detector (ECD). Sensitive and selec-
tained at a temperature greater than 100 °C in order to prevent
tive for halogenated and other electronegative compounds, the
water condensation. Sensitivity of the EFID was similar to that
electron capture detector (ECD) remains one of the most widely
of the FID, but detectivity was improved by a factor of 2.
used GC detectors. Novel applications reported during the past
Other developments included a dual-channel detector in which
two years include the following: the shipboard analysis of
the effluent from a reactive flow luminescence detector (RFD)
halocarbons in seawater and air for oceanographic tracer studies
was burned to form a tandem, stable, air-rich flame ionization
(I39), the determination of chlorobutanol in mouse serum, urine,
detector, providing dual response of compounds from a single
and embryos (I40), the measurement of organochlorine com-
separation (I11). Fundamental research on the FID has included
pounds in milk products (I41), the identification of pesticides and
a mechanistic study of isotope and heteroatoms affects on the
other organochlorides in water (I42), organochorine pesticides
relative molar response (RMR). RMR did not change when
in edible oils and fats (I43), metabolites from permethrin, and
deuterium was substituted for hydrogen in most hydrocarbons
cypermethrin in foods (I44), and the determination of phenols
(I12). The fast response time of a flame ionization detector was
from aqueous solutions as bromo derivatives (I45). A brominated
internal standard was found to be useful for the determination of
(b) Helium Ionization Detector (HID). The helium ioniza-
organochlorine pesticides (I46).
tion detector (HID) was most often used for the detection of inert
In more fundamental studies, a nonradioactive ionization
gases (I14). In one example, traces of Ar and N2 were determined
source was compared with a radioactive source. Initially, the
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
nonradioactive source was found to be 20 times more sensitive
personal chemical warfare detector (I66). In addition, IMS has
than the radioactive source, but after 9 months of use the
been used as a detection method after pyrolysis GC. With this
sensitivity of the nonradioactive source decayed to levels equiva-
system, bacillus spore detection was achieved through the
lent to the radioactive source (I47). In a similar study, it was
characteristic pyrolysis decomposition products of the spores,
found that a pulsed discharge electron capture detector, a
which were identified as dipicolinic and picolinic acid. The
nonradioactive source, was more sensitive than the radioactive
detection limit was found to be on the order of 100 ng of bacillus
source for most compounds, covered a wide dynamic response
Other IMS investigations have included the
range similar to the radioactive source, and demonstrated a
development of an IMS with an internal gas chromatographic
temperature dependence similar to that of the radioactive source.
column (I68) and IMS detectors using tritium ionization and
A kinetic description of the detector response was provided (I48).
photoionization sources (I69).
Amine response in a radioactive source demonstrated that the
(h) Glow Discharge Detector (GDD). A novel detection
relative molar sensitivity factor, TM, was correlated with the pKBH
method investigated for GC was glow discharge ionization (I70).
of the individual amine (I49). Finally, it was noted that the
The effect of discharge gas on the GC response was reported
addition of ammonia to the nitrogen makeup gas in amounts as
(I71), along with analytical characteristics for organic compounds
large as 20% increased the response for various chlorinated
(I72). Glow discharge detectors have also been used as ionization
sources for gas chromatography/mass spectrometry (I73). (e) Surface Ionization Detector (SID). Over the past few Mass Spectrometric Detectors. Is gas chromatography an
years, surface ionization detectors have been given considerable
inlet for mass spectrometry, or is mass spectrometry a detector
attention for the determination of organic compounds with low
for gas chromatography? In past gas chromatography reviews,
ionization potentials. Recently, however, a novel design for surface
the former concept prevailed, and the review of GC/MS methods
ionization detection was reported based on hyperthermal positive
was covered only in the mass spectrometry section. Today,
surface ionization (I51-I54). The primary requirement for the
however, given the growth in number of applications for which
operation of this detector was the use of a supersonic free jet
GC/MS instruments are well suited, the decrease in size and
nozzle to introduce the sample to a high-work-function surface of
required operator expertise, and the increase in reliability and
rhenium oxide. The primary advantage of this new SID is that it
ruggedness, mass spectrometry has become a simple but powerful
produced a higher sensitivity for all organic compounds, providing
detector for gas chromatography. Thus, for the first time, mass
a universal GC response. Detection limits of 10-13 g/s for pyrene
spectrometers are reviewed in this section along with other
and 10-12 g/s for toluene were reported, with a linear dynamic
standard, routine gas chromatographic detectors. While all mass
range of 106. A second surface ionization detector provided a
spectrometric detectors fall into the category of ionization detec-
unique sensitivity for tertiary amines, with detection limits down
tors, they have been split into a separate category in this review
to 10-14 g/s (I55, I56). Finally, a GC/SID system was reported
due to the breadth of ionization mechanisms and GC applications
for the detection of underivatized codeine and dihydrocodeine
reported in the literature during the past two years. These mass
(I57), strychnine (I58), and various benzamides (I59) in body
spectrometric detectors (MSDs) have been separated according
to their ionization mechanisms for this review. (f) Photoionization Detector (PID). Although some method (a) Electron Impact Ionization. Electron impact ionization
development using PID was reported, such as the monitoring of
is, of course, the oldest of the ionization methods currently used.
volatile contaminants in wastewaters (I60), much of the research
Its mechanism is well understood, and the fragmentation patterns
revolved around the development of novel photoionization detec-
produce valuable information for the identification of organic
tors. One study incorporated the use of selective photoionization
compounds. GC/MS applications using this ionization source
detectors with nonselective detectors to provide both quantitative
have been developed for environmental (I74-I82), agricultural
and qualitative information about the sample (I61). Another used
(I83-I85), food science (I86-I88), biological (I89-I100), forensic
a variety of rare gases to identify and quantify unknown com-
(I101), petroleum (I102, I103) and industrial (I104, I105) samples.
pounds (I62), while a pulsed discharge in He was demonstrated
On a more fundamental level, a novel ionizer was reported (I106),
as a He photoionization detector with a selective photoionization
and region II of the a/q stability diagram was used for fast
mode of operation (I63). The measuring chamber arrangement
scanning of a linear quadrupole mass spectrometer. The purpose
of a photoionization detector was modified by dividing the main
of this experiment was to evaluate this method as a means of
chamber into several smaller volumes, permitting these smaller
detection for high-speed gas chromatography. Scan rates of 1000
volumes to share a common anode and cathode (I64). Benzene
scans/s were obtained, with mass spectral peaks resolved over
relative response factors for the PID were reported in which
energy models were developed using HyperChem and compared
Using ion trap mass spectrometry (ITMS) with GC/MS,
airborne carbonyl compounds were separated and detected as
(g) Ion Mobility Detector (IMD). The number of applica-
their pfbha oximes (I108), residues of chlorinated pesticides in
tions of ion mobility spectrometry as a detector for gas chroma-
eggs of the gray heron were identified (I109), and pesticides in
tography continues to grow. Over the past two years, much of
the marine environment at the low nanograms per liter level were
the emphasis on ion mobility detection after gas chromatography
determined (I110). Novel developments in ion trap mass spec-
as been in the area of portable analytical instruments. Many of
trometers included a three-dimensional quadrupole ion trap
the IMS references are discussed in that section of this review.
coupled to a capillary GC (I111) and the addition of a sample
One major thrust in the development of GC/IMS has been as a
inlet with a pressure working range from 1 to 1000 mbar (I112).
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
Isotope ratio mass spectrometry was used with GC for the high-
time-of-flight mass spectrometry was reported with isomer-
precision D/H measurement from organic mixtures (I113) and
selective multiphoton ionization (I135, I136).
the determination of 15N of N2 and N2O in soil atmosphere (I114). Optical Detectors. As with ionization detectors, optical
In general, gas chromatography was coupled to isotope ratio mass
detectors fall into a wide range of categories. Atomic and
spectrometry via a combustion furnace (I115, I116).
molecular absorption and emission provide multiple approaches
(b) Chemical Ionization. Chemical ionization, a less ener-
for both qualitative and quantitative information from samples
getic ionization method than EI, is often used with EI to aid in
identifying the molecular ion and to increase the sensitivity of a
(a) Atomic Absorption Detectors. Coupling gas chroma-
method. As with the EI source, fundamental investigations of the
tography to atomic absorption spectrometry (AAS) provided
ionization mechanism have been extensive, but novel GC/MS
selective detection for many compounds. Tetramethyllead and
applications are still being developed. 4-(Carbethoxy)hexafluo-
tetraethyllead were used as test analytes in the evaluation of a
robutyryl chloride was used for the derivatization of ethylene
quartz tube atomizer (I137). A comparison of GC/AAS with
glycol from human serum. This derivatization product produced
differential anodic stripping voltametry for organolead was re-
a distinct protonated molecular ion peak at m/z of 563, providing
ported (I138). A simple and reliable method for the detection of
an unambiguous confirmation of ethylene glycol (I117). When
organolead compounds in a water sample was developed (I139).
ammonia was used as a reagent gas, direct and rapid characteriza-
GC/AAS proved to be especially useful for the speciation of
tion of paraformaldehydes after pyrolysis gas chromatography was
organomercury compounds. Mercury speciation in natural water
possible (I118). Solid-phase extraction and positive chemical
samples (I140) and in human body fluids (I141) was reported.
ionization mass spectrometry were used for the analysis of cocaine
GC/AAS was also applied to the analysis of organotin species
and its metabolites (I119). Other positive chemical ionization
(I142). A novel atomic absorption technique after gas chroma-
methods included identification of higher alcohols in cosmetics
tography was reported using a microwave-induced plasma for the
(I120) and the characterization of low-molecular-weight polyeth-
determination of chlorinated hydrocarbons (I143). In addition,
yleneimines (I121). Negative ion chemical ionization was used
element-selective diode laser plasma detection for chlorinated
to analyze R- and -endosulfan in biological samples by selectively
compounds was reported (I144).
monitoring the product ions at m/z 35 and 37. The selectivity
(b) Atomic Emission Detector (AED). The most utilized
and sensitivity of negative ion chemical ionization were demon-
GC detector based on optical mechanisms was the atomic
strated by the direct measurement of endosulfan in mouse brain
emission detector (AED) (I145-I148). It was especially useful
without purification of samples (I122). Electron capture negative
as a complementary analytical technique to GC/MS for environ-
ion chemical ionization was used for the analysis of 5-methox-
mental screening (I149) and for the separation and detection of
organometalic compounds (I150, I151). With respect to organo-
For improved selectivity and sensitivity, GC was coupled to
metalic compounds, a number of analytical methods were reported
MS/MS instruments. The primary advantage is that a sharp, well-
for the determination of organomercury (I152-I157) and orga-
resolved GC peak is produced for quantitative analysis, and a
notins (I158, I159). Other applications included the determination
simple, unambiguous spectrum is available for qualitative confir-
of chlorophenols in tap water (I160), measurement polychlori-
mation (I124). With this method, as low as 10 pg of an isotope-
nated and polybrominated biphenyls in the environment (I161,
labeled amino acid was detected in 20 ng of the endogenous
I162), and herbicide analysis in soils (I163).
compound (I125). In another example, phosphate esters in diesel
Fundamental studies of the AED were also reported (I164).
exhaust were detected and confirmed (I126).
Parametric investigations included temperature effects on quan-
(c) Inductively Coupled Plasma Ionization. A powerful
tification (I165) and makeup gas flow on emission (I166). A
technique for the separation and speciation of volatile organo-
round-robin robin study demonstrated that intralaboratory pro-
metalic compounds is capillary gas chromatography coupled to
cedures ranged from 1.3 to 22% RSD and that interlaboratory
inductively coupled plasma mass spectrometry (ICPMS) (I127).
results ranged from 11 to 40% RSD (I158). Elemental C/Cl and
The primary advantage of GC-ICPMS is that the total analyte
C/Br ratios deviated by less than 20% from calculated values
was transferred into the ICPMS without loss due to nebulization
(I128). Several methods for coupling a GC to an ICPMS have
Development and evaluation of several novel analytical systems
been reported. In one case, the interface did not require any
were reported. A direct-current AED was described for use with
changes in the ICP and could be completed in less than a minute
gas chromatography (I168). Pyrolysis/GC/AED was demon-
(I129). For alkyltin compounds, coupling was accomplished with
strated by the determination of silicones in air down to the 0.1
a heated stainless steel transfer line (I130). A heated transfer
ng/L level (I169). Also, an LC/GC/AED system provided a high-
line made from quartz was also reported (I131). Applications of
efficiency separation for analytes in a complex sample matrix
GC/ICPMS have included organometallics from river and harbor
sediments (I132) and the speciation of organolead compounds
(c) Molecular Absorption Detectors. The use of molecular
from environmental waters (I133). One interesting application
absorption detectors in gas chromatography is less common than
was the detection of dimethylselenium in human breath in the
other optical detection methods. The primary approach is IR
detection. Analysis of cis- and trans-fatty acid isomers after
(d) Laser Ionization. Normally, laser ionization methods are
separation by capillary GC was reported to be simple and fast,
used for large nonvolatile compounds. However, the combination
but its lower detection limit of 5% limited it use (I171). In some
of gas chromatography, supersonic beam UV spectroscopy, and
cases, sensitivity limitations could be overcome by the use of large
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
Table 3. Applications of Multiple Detectors
pesticide residues in fruits and vegetables
organophosphorus and organonitrogen pesticides
cyclic hydrocarbon pollutants from combustion gas of coal
injection volumes (I172). Fourier transform methods can also
Its lower detection limit was approximately 200 ppb (I200).
improve detection limits (I173, I174). The most sensitive ap-
Miscellaneous and Multiple Detectors. Miscellaneous GC
proach is matrix-isolation IR spectrometry, but the instrument is
detectors not conveniently included in categories discussed above
more complicated, and chromatographic resolution may be
are covered in this section. An acoustic flame detector (AFD)
reduced (I175). In a unique approach, diffuse reflectance Fourier
for gas chromatography monitored the frequency of the sonic
transform infrared spectrometry was coupled with GC (DRIFT-
bursts from a flame. Shifts in the frequency were indications of
GC) for catalyst characterization (I176).
analyte presence in the flame (I201). Olfactometry (OD) is one
Another molecular adsorption technique coupled a packed
of the oldest detection methods for GC, and still, novel methods
column with a UV-visible molecular absorption spectrophotom-
were reported (I202, I203). Electrolytic conductivity detection
eter for the detection of benzene, toluene, 1,4-xylene, 1,2-xylene,
(ElConD) coupled with solid-phase extraction was used for the
and mesitylene (I177, I178). In addition, the determination of
trace analysis of vinclozoline (I204). Radiochemical detectors
isoprene in human breath was reported by thermal desorption
were used for special applications (I205-I207) and, in a few
gas chromatography with UV detection (I179).
specific cases, GCs were interfaced to a nuclear magnetic
(d) Molecular Emission Detectors. The flame photometric
resonance spectrometer to provide molecular structural informa-
detector (FPD) is, by far, the most common molecular emission
tion on the analyte (I208, I209). Semiconductor detectors were
detector. Routinely used for the determination of tin- (I180-
investigated to replace the FID (I210) and for breathalyzers
I185), lead- (I186), germanium- (I187-I189), nitrogen- (I190),
(I211). Finally, improvements in thermal conductivity detectors
sulfur- (I191), and phosphorus- (I192) containing compounds, ithas the option of multichannel response (I193, I194). An
(TCD), for years the primary detection method for gas chroma-
improved performance of the detector was demonstrated using a
tography, were reported for sensitivity (I212) and for interfacing
pulsed mode of operation and optimal operating conditions (I195).
with capillary columns (I213, I214).
Miscellaneous chemiluminescene detectors were reported as
The ability to combine GC detectors in a single analysis is a
well. The determination of trace amounts of organic explosives,
powerful approach for the investigation of complex mixtures and
in which 0.2 ng of HMX was detected, was accomplished using a
the identification of unknown compounds. The combinations of
thermal energy analyzer (TEA) (I196). One detector, called the
detectors shown in Table 3 were used in novel ways to solve
sulfur chemiluminescene detector, was based on the principle of
analytical problems during the past two years.
the formation of sulfur dioxide in a reducing flame. The sulfurdioxide is then detected by its chemiluminescence reaction with
Gary A. Eiceman is a Professor in the Department of Chemistry and Biochemistry at New Mexico State University in Las Cruces, NM. He
ozone (I197). Mechanisms were also discussed in the literature
received his Ph.D. degree in 1978 at the University of Colorado, was a
(I198). Application of the detector was reported for volatile sulfur
postdoctoral fellow at the University of Waterloo (Ontario, Canada) from1978 to 1980, and joined the faculty at NMSU in 1980. In 1987-1988,
compounds in water, with a linear response from 10 to 100 µg/L
he was a Senior Research Fellow at the U.S. Army Chemical ResearchDevelopment and Engineering Center (Aberdeen Proving Grounds, MD)I199). A selective chemiluminescene detector after GC was also
and is a visiting lecturer at the Universidad Autonoma de Chihuahua
applied to the detection of nitrogen compounds in crude and
(Mexico). His research interests include the development of gas chro-matography for environmental analyses, the advancement of GC/ion
refined petroleum fractions. This detector was based on initial
mobility spectrometry for chemical separations, and the creation of
pyrolysis combustion at 1100 °C in the presence of oxygen,
chromatographic phases from natural materials such as clays. He teachesinstrumentation and electronics, quantitative analysis, and freshman
followed by a luminescence reaction of the product NO with ozone.
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
Jorge L. Gardea-Torresdey is an Associate Professor of Chemistry
(B15) Roshina, T. M.; Davydov, V. Y.; Khrustaleva, N. M.; Mandrugin,
at The University of Texas at El Paso in El Paso, TX. He received his
A. A.; Gurevich, K. B. Adsorpt. Sci. Technol. 1997, 15(3), 147- Ph.D. in 1988 at New Mexico State University in Las Cruces, NM. Hisresearch interests presently include environmental chemistry of hazardous
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(B17) Naito, K.; Yasukiyo, E.; Sadaaki, M.; Shinsuke, T. Anal. Sci.inductively coupled plasma/mass spectrometry, and investigation of metal1995, 11(2), 303-305. binding to biomaterials for remediation of contaminated waters and soils
(B18) Nan-Tran, H.; Gander, B.; Nguyen, V. P.; Gentili, S.; Sabra, F. (through phytoremediation). He has authored or coauthored over 70J. Phys. Chem. 1995, 99(11), 3806-3809. research articles and book chapters and holds three U.S. patents for
(B19) Zhu, C.; Kwang, S. Y.; Jon, F. P. Anal. Chem. 1995, 67(9), environmental remediation. He has taught analytical chemistry andinstrumental analysis at the undergraduate level and advanced analytical
(B20) Hadjar, H.; Balard, H.; Papirer, E. Colloids Surf., A 1995, 99(1), chemistry and environmental chemistry at the graduate level.
(B21) Khan, M.; Afzal, M. Pak. J. Chem. Soc. Pak. 1996, 18(2), 72- Herbert H. Hill, Jr., is a Professor of Chemistry at Washington State
(B22) Shalaeva, M. E.; Zheivot, V.; Prokudina, N. A.; Chesnokov, V. University. His research interests include gas chromatography, super-
V.; Malakhov, V. V. J. Anal. Chem. (Transl. of Zh. AnaI. Khim.)critical fluid chromatography, ion mobility spectrometry, ambient pressure1996, 51(6), 560-564. ionization sources, and mass spectrometry. He received his B.S. degree
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(B24) Ji, Z. C.; Imogene, L. J. High Resolut. Chromatogr. 1996, 19(1), from the University of Missouri, Columbia, MO, and his Ph.D. degree in1975 from Dalhousie University, Halifax, Nova Scotia, Canada. In 1975,
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Books and 1. Lombardi E, Massai C, Orlandini D, Vierucci A. Patologia respiratoria associata Chapters of Books (Dal a dermatite atopica al ’asma/rinite). IN: Vierucci A, ed. “Edit-Symposia Al ergologia - Dal a dermatite al ’asma”. Editeam, Bologna, 2002;31-41. 2. Lombardi E, Orlandini D, Vierucci A. La patologia sibilante nel bambino. IN: Vierucci A, ed. “Al ergologia pediatr
SPECIAL MEDICARE WATCH May 22, 2008 ===================== 1. Globe and Mail (May 22, 2008) Centralization: a step back for Alberta health care? Premier must explain how ending regionalization will improve innovation, access and quality of care By Andre Picard 2. Government of British Columbia (May 21, 2008) Ministry of Health - News Release & Backgrounder Government Accepts Drug Plan Recommend