Gas Chromatography

Anal. Chem.  2010,  82,  4775–4785

Gas Chromatography Frank L. Dorman*

Department of Biochemistry and Molecular Biology, Penn State University, University Park, Pennsylvania 16802  Joshua J. Whiting

LECO-ARD, Saint Joseph, Michigan 49085  Jack W. Cochran

Restek Corporation, Bellefonte, Pennsylvania 16823  Jorge Gardea-Torresdey

Department of Chemistry, University of Texas, El Paso, El Paso, Texas 19968  Review Contents

General Interest and Reviews  Texts Review Articles Columns Principles and Technology General Information Stationary Phases Fundamental Characterizations Portable and Microfabricated GC Technology  Development Microfabrication Developments Comprehensive Two-Dimensional Gas Chromatography  (GC  × GC) Scope Reviews Instrumentation Data Handling  Theory Biological Clinical and Forensics Environmental Flavor and Fragrance Food and Beverage Metabolomics Petrochemical Gas Chromatography Detectors Impr Im prov ovem eme ent in GC De Dete tect ctor or Te Tech chni niqu que es GC Detector Improvement through Software Development Development of GC New Detectors Literature Cited

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GENERAL INTEREST AND REVIEWS  This review of the fundamental developments in gas chromatography (GC) includes articles published following the previous review rev iew ( 1 ) in 2008 up to March, 2010. Emphasis is given to developments which are considered significant as far as basic advances. This accounts for a much smaller amount of publications, as the majority of papers deals with applications of the GC technique and, as such, do not necessarily represent advances in * To whom correspondence should be addressed. 10.1021/ac101156h ©  2010 American Chemical Society Published on Web 05/26/2010

the fundamentals. A recent search of the literature had slightly  more that 800 publications per year that have the broad subject  area of “gas chromatography”. Most of these publications are applied separations which use GC as the separation technique, so this review really focuses on the small subset that are viewed by the authors as improvements in the technique or the understanding of the techniqu technique. e. Despite the large numbers of publicationss in oth tion other er sep separa aratio tion n tech techniqu niques es (HP (HPLC, LC, CE, etc etc), ), GC is arguably still the best separation tool that is in common use for  the compounds which are amenable to the technique. Possibly, the greatest expansion of this technique that attracts interest from researchers is comprehensive two-dimensional GC (GC ×  GC). Increasing interest from the commercial field has led to additional instrumentation and improvements in ease of use following the previo pre vious us rev review iew.. Whil Whilee this technique technique is stil stilll not common in analytical laboratories, it does account for a significant amount of  the publications and academic research; thus, it occupies a rather  extensive portion of this review.  Texts.   Several texts were published in this period, some of   Texts.  which were revised editions. Of particular note are three first  edition texts: “Comprehensive Two Dimensional GC”, edited by  Ramos (  2  ); “Quantification in LC and GC: A Practical Guide to Good Chromatographic Data”, edited by Kuss and Kromidas ( 3 ); and “Ionic Liquids in Chemical Analysis”, edited by Koel ( 4 ). Also revised revi sed during this per period iod was McNa McNair’ ir’ss tex textt on “Ba “Basic sic Gas 5 ),   which is a text that is often used in the Chromatography Chromat ography”” ( 5  teaching of the GC technique to students. Finally, for the GC/ MS technique, Hubschmann has revised and updated the Handbook of GC/MS text ( 6  6 ).   During the tim timee pe peri riod od of thi thiss re revi view ew,, Review Articl Articles. es.   During approximately 40 review articles were published on various aspects of GC. Many were, again, application driven, or were focused on detection strategies or increasing the instrumental throughput.  There were a surprising number of articles, however, that were more focused on the GC separation itself or on expanding the range of compounds which can be analyz analyzed. ed. Often referred to as Analytical Chemistry, Vol. 82, No. 12, June 15, 2010   

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the “Achilles heel” of GC, the injection technique can be a large source of frustration when analyzing thermally labile compounds. Large volume injection (LVI) methods have been well reviewed ( 7 )  including direct sample introduction and through oven transfer  adsorption desorption (TOTAD) techniques.  Also considered an “injection” technique, static headspace extraction GC (SHE-GC) was reviewed ( 8 ). Methods of extending the working range of volatility for this technique are addressed, and good coverage of the fundamentals is also summarized. Fast GC was also reviewed ( 9 )  with particular attention being paid to theory and influence of various band-broadening mechanisms which can potentially limit this technique. It was demonstrated that peak widths of 1 ms are readily achievable in GC if  extra-column band broadening is controlled.  A few reviews concerning the role and understanding of the stationary phase in GC separations were published. The first  describes the various retention models used in prediction of  retention times based on thermodynamic parameters ( 10  ). This also covers the use of thermodynamic modeling to various column arrangements with simultaneous temperature and pressure programming. Also discussed is extension of these techniques to fast  GC and GC ×  GC. Most of the stationary phase work published still continues to be nonpolysiloxane materials, and a review of  molten salt and ionic liquids as stationary phases for organic compound analysis includes a discussion as to how stationary  phases should be selected by potential users ( 11 ). A review of  the use of metal-containing stationary phases was also published ( 12  ). These materials are useful for separation of compounds through a complexation mechanism. Examples of chiral separations were addressed. Finally, several reviews on the GC ×   GC technique were published. The use of this technique for the analysis of complex metabolomic samples was reviewed ( 13 ). This is a very challenging analysis in biological fluid, and the increase in peak capacity  of the GC  ×  GC technique may lend considerable benefit to these separations. Further, coupling the GC ×  GC to a time-of-flight mass spectrometer (TOFMS) adds another dimension of separation and can be a very powerful analytical technique. Two other general reviews of the GC ×  GC technique also summarize the state of  the art of this technique and show numerous relevant applications.  The first includes an industrial perspective as to the benefit of  GC ×  GC in semiroutine analyses at Dow ( 14 ). The second also includes a discussion of the prediction of separation based on thermodynamic properties and attempts to simplify the column selection process ( 15  ). COLUMNS PRINCIPLES AND TECHNOLOGY General Information.  While the GC column is, of course, the only part of the entire GC system that physically separates compounds from each other, only a small percentage of  publications deal with the understanding of this process or the development of new materials. While this may have been a very  active area of research years ago, it certainly is viewed as “mature” in the present day, and as a result, most publications that fit into the category of column advancements are very niche in application. Professor Klaus Unger was quoted at the HPLC 2008 meeting as saying that “we should put our efforts towards gaining selectivity, not towards the mad rush to increase efficiency”. He was, of course, discussing the area of small4776

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particle based HPLC separations, but his comments could easily  apply to GC as well. Most practicing chromatographers have little interest or knowledge in the mechanisms which lead to separation and often rely on detection techniques to overcome chromatographic coelutions. While this may give acceptable results in some cases, there is still need for development of  new materials which would give additional selectivities and/ or allow GC to extend further into the analysis of reactive nonvolatile compounds. Stationary Phases. Clearly, ionic liquids continue to represent  the highest percentage of papers published using new materials as GC stationary phases. To date, these materials have not had the efficiency of the polysiloxanes, but they do offer unique selectivities. The use of ionic liquids has been reported in the analysis of biodiesel blends ( 16  ), another recent topic of interest!  This paper uses one of the commercially available columns which is based on the chemistry developed at Dan Armstrong’s group.  The comparison to more standard poly(ethylene glycol) (PEG) column separations demonstrates the ionic liquid’s benefit of  separation of the FAME’s from the less-retained saturates. Other  researchers have reported on an ionic liquid bonded polysiloxane stationary phase, which they claim has a “high separation efficiency” of 3200 plates/m ( 17  ). Finally, the development of a  new triflate ionic liquid for GC ×   GC was reported ( 18 ). The comparison to more conventional PEG phases as second-dimension columns was discussed. The ionic liquid column was stated to have significantly larger selectivity for several of the test  compounds. Second dimension column orthogonality is a very  important issue for GC ×  GC separations, and ionic liquids may  have a role here, even if their efficiencies are not as high as more routine phases.  The separation of polycyclic aromatic hydrocarbons (PAH’s) has been of increased interest. Several commercial companies have reportedly developed columns specifically for this application. Most notable, Agilent Technologies (www.agilent.com) and Varian (www.varian.com) have marketed a specific column for this separation. Restek Corporation (www.restek.com) has also reported on the use of molecular modeling techniques to develop a  new material that is designed for this separation ( 19  ).  Addi tional work in the area of modified cyclodextrines was still an area of research, and one paper (  20  ) discussed the use of a maltooctaose derivative as a stationary phase for the separation of enantiomers. Another one (  21 ) used a common permethylated β-cyclodextrine diluted in a variety of liquid phases in order to determine the role of the polymer type on retention. This work used PEG and also SE-30 and SE-54 as liquid phases. Fundamental Characterizations. During this review period,  very little work was published on the modeling or characterizations of stationary phases. Typically, there have been a few papers on thermodynamic modeling and also quantitative structure property relationship (QSPR) approaches. There were two papers published, both using QSPR models for retention prediction of   22  ), the environmentally important compounds. In the first (  retention indices of 168 pesticides were used to construct a QSPR  model. The second paper (  23 ) used a QSPR approach to determine four optimal descriptors which then let the authors predict retention on 18 different GC columns for all 209 PCB

Figure 1. Number of citations by year of Terry, Jerman, and Angel’s 1979 paper describing the first etched silicon GC system.

congeners. These approaches should allow for improved column selection and also potential identification of congeners that may  not be in a particular user’s calibration standards. PORTABLE AND MICROFABRICATED GC TECHNOLOGY DEVELOPMENT  Analytical samples are often at risk for sample contamination, decomposition, degradation, and loss during storage and transport  from the collection site to the laboratory for analysis. This has resulted in a growing trend toward efforts to bring the lab to the sample when possible. Significant efforts have been invested to develop and test portable instrumentation. There have been several recent reports of the development and use of portable GC systems including work done at the University of Michigan on a  portable GC with a chemiresistor array detector (  24 ). The system  was designed for rapid, trace analysis of complex mixtures. It  consists of a small, multistage preconcentrator; two series-coupled columns with fast, independent temperature programming capabilities; pressure control at the junction point between the columns; and an array of chemiresistors for detection. A new  commercially available portable GC with detection provided by a  toroidal ion trap mass spectrometer has been developed and described by researchers at Brigham Young University and Torion  Technologies (www.torion.com) (  25  ). The system consists of a  SPME injection system, a low-thermal mass GC, and a miniature toroidal ion trap mass analyzer housed in a Pelican case. The entire system including pumps and batteries weighs about 13 kg.  Two other application studies included the use of portable GC systems for the analysis of acetaldehyde in tobacco smoke (  26  ) and the clinical measurement of volatile sulfur compounds (VSCs)  which can be a cause of oral malodor (  27  ). Microfabrication Developments.   Thirty years after the publication of the seminal paper by Terry, Jerman, and Angell in 1979 (  28 ), which described the first GC system composed largely  of microfabricated components, interest in separation systems facilitated by microfabricated devices continues to grow as micromachining capabilities mature. Evidence of this is shown in Figure 1 which shows the number of citations of the Angell paper as a function of publication year. The promise of this research continues to be reduced system size, low-power requirements, enhanced performance, and the promise of batch manufacturing to reduce costs. In practice, significantly enhanced

performance continues to elude researchers, with the best  performing microfabricated columns performing on par with comparable commercially coated fused silica columns. These performance challenges were largely predicted by Golay in 1981 (  29  ) when he described the end effects of high aspect ratio columns. As novel geometries and fabrication techniques evolve, the potential exists for greater improvement in these areas. Even  within these current limitations, interest remains high due to the promise of reduced manufacturing costs by utilizing similar batch manufacturing techniques now common in the semiconductor  industry for the manufacturing of microprocessors, memory, etc. However, an important consideration, as the number of researchers developing new stationary phase coatings, coating techniques, column designs, and methods of fabrication increases, is that a  standardized column evaluation method should be developed to directly compare their performance and test column reproducibility.  The size and power benefits are both obvious and connected; as one reduces the mass of components, the power required to heat and cool individual components decreases as well. Several GC systems have been designed and manufactured using microfabricated components to achieve this end. Examples include the Canary line from Defiant Technologies (www.defiant-tech.com)  which integrates microfabricated GC columns, preconcentrators, and detectors for multiple applications; SLS micro’s GCM series (www.slsmt.com) which integrates a microfabricated column, detector, and sample loop along with the electronics into a PDA  sized fluidics package; and Thermo Scientific’s C2 V-200 micro GC (www.c2v.nl) which integrates a microfabricated inlet and detectors with conventional wall coated open tubular fused silica  columns. Two recent developments include the introduction of  an “intelligent” preconcentrator by Defiant Technologies that “onthe-fly” determines the appropriate sampling time and the acquisition of Concept to Volume (C2 V) by Thermo Scientific. Several researchers continue to work on the development of new systems based on microfabricated components; one recent report describes a new portable GC system utilizing a micro electromechanical system (MEMS) enabled miniaturized GC for the subparts per  billion detection and monitoring of aromatic volatiles ( 30  ). Zampolli and others at the CNR-IMM Institute for Microelectronics and Microsystems in Bologna, Italy, describe a system consisting of a micromachined preconcentrator, a 50 cm ×  800  µ m  ×  1 mm microfabricated column packed with 80-100 mesh carbograph 2 +  0.2% carbowax particles, and metal oxide (MOX) gas sensors as a detector. The demonstrated system shows separation of BTEX  compounds in about 10 min. Another report by Nishino and others at Shimadzu describes the development of a prototype instrument  built around a microfabricated column 8.5-17 m in length generating 35 000 theoretical plates with a flame ionization detector (FID) ( 31 ). There remain several research programs focused on the development of new MEMS GC systems including Sandia National Laboratories and the University of Michigan  WIMS Center. Sandia National Laboratories has had an ongoing development  program in the area of microfabricated GC systems since 1996, primarily geared toward the rapid, portable, low-power detection of chemical weapons, explosives, and more recently toxic industrial chemicals. Recent advances include the development of masssensitive microfabricated preconcentrators ( 32  ), a new selective Analytical Chemistry, Vol. 82, No. 12, June 15, 2010 

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and sensitive chemiresistor GC detector ( 33 ), and the demonstration of the first consumable free comprehensive two-dimensional GC system (GC ×   GC) consisting of a pair of microfabricated columns and a microfabricated detector ( 34 ). The mass-sensitive preconcentrator consists of a thin film resistive heater on the surface of a MEMS pivot plate resonator (PPR). The PPR is Lorentz force actuated, and the frequency of the resonator shifts  with mass loading. When sufficient sample has been collected for  analysis by the downstream microfabricated gas analyzer, the film is heated and the sample is desorbed. Under partial funding from the Defense Advanced Research Projects Agency Micro Gas  Analyzer (DARPA-MGA) program, Sandia developed a sensitive chemiresistor utilizing a conjugated molecule linked gold nanoparticles in a sol-gel matrix. The chemiresistor demonstrated significant selectivity for phosphonates (CWA simulants) and sensitivity. The GC ×   GC utilized a pair of microfabricated GC columns. The first column was coated with polydimethyl siloxane and was 90 cm in length; the second column was 30 cm in length and was coated with polyethylene glycol. The modulator was a  stop-flow design based on the work of Richard Sacks, and detection was provided by a nanoelectromechanical systems (NEMS) cantilever resonator developed by the Roukes group at  Caltech. The system demonstrated a separation of  29 components in less than 8 s.  The NSF funded Wireless Integrated MicroSystems (WIMS) Engineering Research Center (ERC) (www.wimserc.org) is in the final year of NSF funding for the center and is transitioning from an ERC to the WIMS institute. The center has been developing several parallel MEMS GC based systems for multiple applications, such as breath analysis ( 35  ), explosives detection ( 36  ), extraterrestrial exploration ( 37  ), and indoor air quality monitoring ( 38 ).  They have developed new gas phase detectors such as nanoscale chemiresistor arrays ( 39  ) and microdischarge detectors ( 40  ). The  WIMS center has also demonstrated the first thermally modulated GC ×  GC system utilizing microfabricated columns ( 41 ).  While these efforts continue, much of the research being reported has focused on the development of microfabricated components such as preconcentrators, columns, and detectors. In the area of preconcentrators, several groups are exploring the use of carbon nanotubes (CNTs) as a sorbent material. CNTs demonstrate excellent adsorption and desorption characteristics due to low mass transfer resistance because of the nonporous nature of the material ( 42 ,  43 ). Other materials investigated for  use as sorbents in microfabricated preconcentrators include the use of microporous activated carbon ( 44 ), chemically polymerized polypyrrole ( 45  ), as sorbent materials, and inkjet printing of  polymer sorbents prior to anodic bonding ( 46  ). In the area of column development, there have been several reported advances. Zareian-Jahromi and Agah at Virginia Tech have recently reported revisiting the concept of multicapillary  columns (MCCs) ( 47  ). MCCs are a concept first operatively  demonstrated by researchers in Novosibirsk, Russia, in the 1980′s and exist now as a commercial product sold by Multichrom, Ltd. (www.mcc-chrom.com). The principal concept is to get around the column capacity limitations and pressure restrictions of  microbore columns using a bundle of identical microbore columns in parallel. This allows a fraction of each injection to be separated on each column preventing overloading and enables the overall ∼

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flow restriction to be very small. The challenges remain in manufacturing uniform channels, both in length and phase volume ratio, distribution of the injection plug equally to all columns, and dead volume at the inlet and outlet of the system. Problems in any of these areas will result in band broadening. Agah’s group has demonstrated some success using a MEMS approach to address these problems. Ali and Agah have also demonstrated MEMS based semipacked columns ( 48 ). These columns used microfabricated posts in the column channels to decrease diffusion distances and column capacity relative to more traditional WCOT  columns but still demonstrate significantly reduced pressure drops relative to traditional packed columns. Zareian-Jahromi and Agah have also reported a novel coating technique using a monolayer  protected gold stationary phase ( 49  ).  There are several other reports of novel column fabrication development. Radadia and Masel at the University of Illinois describe work on an all silicon column using a gold diffusion eutectic bonding process to bond a silicon lid instead of a Pyrex lid to the silicon channels ( 50  ) and a partially buried microcolumn  with an interesting cross section ( 51 ). Lewis and Milton describe a microfabricated planar glass column with a circular cross section manufactured in two hemispherical halves and bonded using epoxy ( 52  ). Sun and Chen at the Chinese Academy of Sciences report the development of a silicon/Pyrex microfabricated 100  µm × 100 µm ×  6 m column generating 4850 theoretical plates ( 53 ). There are also reports of new column coatings which have also been developed. Researchers from both the University of Washington/Lawrence Livermore National Laboratories ( 54 ) and University of Tokyo ( 55  ) describe the use of CNTs as stationary phases. Nakai et al. from the University of Tokyo also reports on the use of a  functionalized parylene ( 56  ) as a stationary phase. A report by  researchers at the WIMS center at the University of Michigan highlighted an often overlooked aspect of microfabricated columns: column reproducibility. The study compared the performance of several (2-8) columns with different preparations to develop a column coating strategy ( 57  ).  There have been several advances in the area of microfabricated and miniaturized GC detectors including mass analyzers, ion mobility spectrometers (IMS), optical sensors, and microcantilever (MC) arrays. Malcom and Finlay at Micorsaic Systems, Ltd. and the Imperial College describe a microengineered quadrupole mass filter consisting of microfabricated components to fabricate a quadrupole mass filter with dimensions of 35 mm  ×  6 mm ×   1.5 mm ( 58 ). Researchers at the University of Cordoba  describe a system that couples a multicapillary column with a  miniaturized IMS for rapid GC  ×  IMS separations ( 59  ). Researchers from the University of Missouri and ICx Nomadics have reported on the use of a optofluidic ring resonator (OFRR) sensor  for on-column detection ( 60 -62  ). The OFRR is a thin walled fused silica capillary. The inner wall of the capillary is coated with a  thin polymer film. The circular cross-section of the capillary forms an optical ring resonator where circulating waveguide modes are supported by total internal reflection of light along the curved inner and outer boundary. The evanescent field extends into the core and is sensitive to the refractive index change induced by  the interaction between the analyte and the stationary phase. Long and Sepaniak at the University of Tennessee report on the use of 

MC arrays for gas phase sensing ( 63 ). MC arrays have similar  response mechanisms to quartz crystal microbalances and surface acoustic wave sensors; however, they demonstrate better mass sensitivity, smaller dimensions, and decreased fabrication costs. COMPREHENSIVE TWO-DIMENSIONAL GAS CHROMATOGRAPHY (GC ×  GC) Scope.   This GC ×   GC review covers literature published mostly from 2009 until the end of April 2010, when it was compiled, but unlike GC ×  GC, it is not comprehensive because of the large number of papers found during the search. The number of papers published in the review period was around 100, about a 10% increase over the last review done for  Analytical Chemistry  across a similar time period ( 64 ). Only select articles of the 100 or so are covered, broken down into distinct topic lines as seen below. Reviews.   Cortes et al. reviewed the achievements in GC × GC across 2007 until October 2008 citing 121 contributions from that period ( 65  ). They noted how GC  ×  GC work has shifted from instrumentation development to practical applications and listed those for petroleum, polymer, pharmaceutical, flavor and fragrance, metabolomics, and environmental. Interestingly, they  commented that mass spectrometry (MS) is the detector of choice, now and in the future, for GC  ×  GC, with time-of-flight (TOF) MS outpacing the quadrupole due to having the faster acquisition rates to define ultra narrow peaks from GC ×   GC but predicted that  the use of differential flow modulation (DFM) will increase (as an alternative to cryogenically modulated systems); DFM is not  inherently compatible with the pumping capacity of most MS systems, with the supersonic molecular beam approach of Amirav  being an exception ( 66  ). DFM should be more appropriate for  field and process instruments that employ alternate detectors such as flame ionization detection (FID). Although we may disagree on predictions for DFM, we concur on one statement in their  review; “beer is a highly popular alcoholic beverage around the  world.” In conclusion, Cortes puts emphasis on the need for  improved quantification and qualitative data analysis software and suggests that computational chemistry methods combined with GC  ×  GC chromatogram structure and retention data for known compounds can yield identifications for unknown components. Hamilton specifically reviewed the use of GC ×  GC to study  the atmosphere ( 67  ). GC ×  GC, especially with MS, is ideally  suited for this research given the complex array of natural and manmade emissions and oxidation products present in the atmosphere. An important observation by the author was the need for sophisticated data handling approaches, including image processing, to deal with the wealth of information generated using GC ×  GC/MS. Instrumentation. Research devoted specifically to modulation hardware was relatively light during the review period, although the group of Shellie contributed a substantial piece on designing flexible, pulsed flow modulation systems ( 68 ). Drawbacks of flow  modulation setups, versus the cryogenic approach, include pneumatic complexity, multiple connecting pieces, baseline instabilities, and lack of flexibility for changing modulation times. In particular, inability to vary the modulation time is problematic for flow  modulated systems due to the potential for wrap-around. Shellie developed a dynamic flow model and employed a postfirstdimension-column restrictor that offsets some of these disadvantages, including allowing different modulation times. That benefit 

can now be added to those already realized in flow modulation: less expensive hardware and no cryogenic fluid use. Pizzutti et  al. derived a better compressed air modulator ( 69  ) from an earlier  model ( 70  ) to address developing countries’ needs for low-cost  systems. While the volatility range is limited for this air modulator,  with breakthrough shown for tetradecane, lower volatility pesticides ranging from Trifluralin to Deltamethrin were successfully  analyzed in grapes with GC ×  GC-ECD. Begnaud et al. modified the Marriott longitudinally modulated cryogenic system (LMCS) to temperature program the cooling chamber in conjunction with the GC oven, which reportedly  increases the modulation efficiency across a wide range of  compound volatilities while simultaneously reducing cryogenic fluid use ( 71 ). The use of the LMCS as the heart of a switchable multidimensional/GC ×  GC system was described and then tested  with compounds important to essential oil analysis and lavender  oil ( 72  ). A microfluidic Deans switch placed after a primary GC column, upstream of the LMCS, allowed selection of either a  longer second column for heart-cutting work or a shorter column for GC  ×  GC. The system was flexible enough to allow switching from heart-cut to GC ×  GC multiple times in one analytical run.  Although not demonstrated, the system is proposed to be especially effective for heart-cut olfactory work, where broader  peaks are necessary for sensory perception. Klee and Blumberg performed flow modulation of methanedoped carrier gas, which allowed direct observation/calculation of second dimension hold-up times in GC × GC ( 73 ). Subsequently, they calculated/visualized retention factors for alkanes and diesel components in both columns for GC ×  GC. Unfortunately, for cryofocusing modulator users, this approach will not   work since methane cannot be trapped with current systems. The tendency for those users to employ stationary phase bleed from the first column as a way to calculate hold-up time was discouraged upon proving that stationary phase bleed was retained (versus methane) by the second dimension column. However, the authors’ setup did not consider an independently temperatureprogrammed secondary oven that could be positively offset versus a primary column oven. Primary and secondary column temperatures were the same in their experiments.  Tobias et al. gave the first report on the coupling of GC  ×  GC to combustion isotope ratio MS and used their system to demonstrate the analysis of steroids relevant to sports performance enhancement ( 74 ). They also suggested applications for  food authentication and environmental pollutant tracing, where sample complexity may make one-dimensional GC insufficient. Data Handling.   Given the high data density of GC × GC, especially when TOFMS is used, the sample complexity that  predetermines GC ×  GC use for an application, and the special needs of the metabolomics community in particular, it is not  surprising to discover reports on data handling outside of what is already provided by an instrument vendor. Vial et al. used dynamic time warping to align second dimension peaks in GC × GC chromatograms, followed by multivariate analysis to distinguish three types of tobacco ( 75  ). Through additional interpretation, marker compounds for a tobacco could be identified via the collected mass spectrometry data. An imaging process technique borrowed from the proteomics field was used to compare fruit  aromas represented by contour plots after analysis by headspace Analytical Chemistry, Vol. 82, No. 12, June 15, 2010 

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solid phase microextraction (SPME) GC ×  GC/MS ( 76  ). Image profiles created by the process can be used for statistical analysis and suggesting sample origin. While seemingly very powerful, the authors noted that any mass spectrometry data collected during GC ×  GC is “off-line” to the imaging software, a distinct  disadvantage compared to other GC ×   GC data processing software. Almstetter et al. used GC ×  GC-TOFMS vendor software that included automated baseline correction, peak finding, spectral deconvolution, and library searching prior to applying retention time normalization and data alignment to compare two strains of   Escherichia coli ( 77  ). They exported peak lists from the vendor  software and aligned peaks with a model fitted to known derivatized fatty acids in the samples, followed by principal component  analysis to achieve metabolic fingerprinting.  Theory. Blumberg and Klee took a critical look at definitions for multidimensional separations, including GC ×  GC, discussing Giddings concepts and proposing a new definition that includes only “analytical separations” ( 78 ). Seeley et al. developed a  simplified solvation parameter model to predict GC ×  GC compound retention behavior on a variety of stationary phase combinations using literature values for solute and stationary  phase descriptors ( 79  ). They saw excellent agreement of the model and experimental GC  ×  GC data and suggested the model could be used to design optimal column setups. Biological. Kalinova´ et al. investigated the male wing gland secretions of a bumblebee parasite, the wax moth   Aphomia  sociella, with SPME GC ×   GC-TOFMS ( 80  ). Bumblebees are important pollinators in greenhouses and are being considered for open agricultural field pollination given the recent decline of  the domesticated honeybee. Chemically understanding gland secretions may allow the creation of effective lures for bumblebee parasite control. GC ×   GC-TOFMS, in conjunction with GCelectroantennographic detection (EAD) and GC-FT-IR, identified several compounds as potential sex pheromones for the wax moth.  With perhaps the most provocative title in this review,  Irresistible  Bouquet of Death, only topped by the keywords,  Carcass Attractive-  ness, Kalinova´ et al. again used SPME with GC ×  GC-TOFMS and GC-EAD, this time to study how burying beetles are attracted to dead mice ( 81 ). GC ×  GC-TOFMS allowed the identification of  sulfur-containing volatile organic chemicals evolved after death that are likely stimulants for carrion location by the beetles.  Although a very interesting read, this is one paper not to be studied over lunch. Clinical and Forensics. GC ×   GC-TOFMS was used to analyze opiates and benzodiazepines in human serum after solid phase extraction and derivatization ( 82  ). Excellent second dimension separations from the higher-concentration matrix interferences were achieved for the subject compounds on the 50% phenyltype column. A limit of quantification of approximately 5 ng/mL   was noted for Flunitrazepam in serum, significant since it is necessary to detect therapeutic levels at  < 10 ng/mL. The authors suggested that the full mass-range approach of TOFMS could allow nontarget compound analysis. This same benefit is desirable in sports antidoping applications for retroactive searches of data  for nontarget compounds and “designer steroids”, as voiced by  the group of Marriott ( 83 ). They thoroughly tested GC × GC TOFMS for anabolic agents in urine and reported limits of  detection below or at the required performance levels set by the 4780

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 World Anti-Doping Agency. Quantification with TOFMS can even proceed on ions chosen after analysis since a full mass spectrum is collected. One of the downsides of TOFMS for this application, though, was its apparent lower sensitivity for higher  m / z  ions in the anabolic agent trimethylsilyl derivatives versus other mass analyzers, such as quadrupoles. This issue can compromise not  only sensitivity if those ions are chosen as quantification masses but also qualitative searches via standard mass spectral libraries. In the latter case, the authors recommend creating TOFMS spectral libraries specific for the antidoping compounds of interest  from authentic reference materials. In breath analysis research for clinical purposes, novel multisorbent needle traps were used for sampling prior to desorption to GC  ×  GC-TOFMS ( 84 ). The needle traps performed relatively   well and could even be autosampled, although they were subject  to rapid contamination in some hospital environments. GC ×  GC TOFMS showed the capability to detect low levels of breath components and the potential for identifying previously unknown compounds. The authors correctly suggested that thicker film columns are necessary for volatiles work (versus the 0.25 mm ×0.25 µm used in their first dimension), both to provide better  analyte focusing during needle trap desorption and to avoid overload of higher concentration components. Hoggard et al. exploited the separation ability of GC × GC TOFMS with sophisticated chemometrics to detect and identify  29 impurities in six samples of commercially obtained dimethylmethylphosphonate (DMMP), a chemical weapon simulant ( 85  ).  They then used statistical analysis to classify the DMMPs, finding that two had identical impurity profiles; the chemical supplier later  confirmed them to be from the same source. On the basis of their  success, the authors will continue to develop these methods for  impurity profiling that support forensic investigations of chemicalattack crime scenes. Environmental.   The electron capture detector (ECD) is  widely used in the analysis of environmental samples for polychlorinated biphenyls (PCBs), toxaphene, organochlorine pesticides (OCPs), chlorinated benzenes (CBs), and other halogenated pollutants, even today, often operated with a parallel dual-GC column configuration. In the parallel dual-column GC-ECD approach, two different stationary phases are employed to enhance selectivity and elucidate possible quantification bias. However, for  unknown reasons to this reviewer, GC  ×  GC-ECD, which is similar  in a “two independent separations” regard, is still a relatively littleused technique for environmental analysis. Muscalu and others recently demonstrated the power of GC ×   GC-ECD when they  analyzed PCBs, OCPs, and CBs in sludge and sediment samples ( 86  ). A 100% dime thyl polysiloxa ne column was used in the first dimension coupled to a secondary column that has selectivity toward mono-ortho and coplanar PCBs. Only 2 of  the 64 PCBs investigated coeluted, congeners 4 and 10 (BZ#s). Given that environmental samples are often extremely complex, the authors investigated the potential for chlorinated dioxins and furans, toxaphene, chlorinated diphenyl ethers, and chlorinated naphthalenes to coelute with the PCBs, OCPs, and CBs of interest. There were no interferences. Standard reference materials of sludge and sediment analyzed with GC  ×  GC-ECD after pressurized fluid extraction and silica and copper treatments, showed acceptable accuracy and precision. In addition,

other compounds, such as polychlorinated alkanes, were seen in the extracts.  A hot topic in environmental analysis is pharmaceuticals and personal care products in waters. GC  ×  GC-TOFMS with SPE was recently used to effect parts per trillion level determinations for  13 pharmaceuticals, 18 plasticizers, 8 personal care products, 9 acid herbicides, 8 triazines, 10 organophosphorous compounds, 5 phenylureas, 12 organochlorine biocides, 9 polycyclic aromatic hydrocarbons (PAHs), and 5 benzothiazoles and benzotriazoles in river water ( 87  ). Although a 5% phenyl ×  50% phenyl column combination gave the best separation for the compounds of  concern, the reverse setup gave a good correlation between second dimension retention times for compounds and their log  K ow  values. This relationship was proposed as an identification confirmation tool. Mao et al. better estimated ecotoxicity of petroleum hydrocarbon mixtures in soil using HPLC-GC ×  GC-FID, versus poorly  performing, simple one-dimensional total petroleum hydrocarbon tests ( 88 ).  The remaining environmental GC ×  GC papers cited here are applications accomplished by taking advantage of the three most  important features of GC ×  GC-TOFMS: chromatographic suppression/elimination of matrix interferences that thwart target or  nontarget compound identification, enhanced sensitivity for trace residue levels through modulation focusing, and having a full mass spectrum for compound identification through interpretation or  library searching. In environmental analysis concerning petroleum samples, structure-of-chromatogram can be added as a benefit. The list includes analysis of: biodegraded crude oil ( 89  ); nonylphenols in groundwater and wastewater ( 90  ); heavy oil from natural seeps into the ocean ( 91 ); benzothiazoles, benzotriazoles, and benzosulfonamides in wastewater, raw sewage, and river water ( 92  ); organic nitrogen compounds in urban aerosols ( 93 ); and organic compounds from wood combustion aerosol nanoparticles ( 94 ). Flavor and Fragrance. Rochat, Egger, and Chaintreau investigated shrimp aroma not only with GC ×  GC-TOFMS but also  with GC-olfactometry (GC-O) and multidimensional (heart-cut) GC/MS with olfactometry (MDGC/MS/O) ( 95  ). Each system had its strong and weak points, and ultimately the techniques were complementary. GC ×  GC had superior sensitivity, which endorsed its use for identification of trace-level odorants noted during GC-O or MDGC/MS/O. Difficulties in retrieving matching odorant  peaks for mass spectral identification from the complex GC  ×  GC chromatogram were overcome to some extent by correlating the linear retention indices from an Adams’ database to retention on the first dimension column of the GC  ×  GC setup. Of course, both stationary phases must be the same for this approach to work, and in one important case, that of attempted confirmation of the intense odorant 2-ethyl-3,5-dimethylpyrazine, even the separating power of GC ×   GC and spectral deconvolution did not resolve interferences that corrupted its mass spectrum. Extracted ion plots and “reverse search” of the coeluted mass spectrum provided tentative identification of the pyrazine. In all, over 40 odorants  were listed for shrimp odor, although with descriptors like “garbage, foot, rancid, dirty socks, awful, not well, etc” for some compounds, one has to wonder if further work will be attempted! From shrimp odor to perfumery, Pripdeevech, Wongpornchaia, and Marriott turned in a report on the use of GC  ×  GC with FID

and quadrupole MS, against one-dimensional GC/MS, to evaluate simultaneous steam-distillation, supercritical fluid, microwaveassisted, and Soxhlet extraction methods for Thai vetiver root ( 96  ).  Vetiver root oil is apparently an excellent fixative for perfumes. Sixty-four compounds were identified using GC/MS with an additional 43 identified (out of the many more separated) with GC ×  GC/MS. Relative quantification for those compounds for  the different extraction methods was done via GC ×  GC-FID.  Tranchida et al. used GC ×  GC with a fast scanning quadrupole MS to characterize fresh and aged tea tree essential oils, including for potential allergenic components, some of which were found in both fresh and aged oils ( 97  ). Although substantial differences  were noted between fresh and aged (or oxidized) oils, many of  the compounds in the oxidized oil went unidentified due to lack of library mass spectral data. In a study on Indian cress (also known as nasturtium) essential oil, GC  ×  GC-TOFMS was used in conjunction with GC-O, mainly  to identify low-level odorants that would otherwise need tedious sample enrichment ( 98 ). Food and Beverage. Food origin and authentication studies are made easier by comprehensive GC approaches, since food samples are typically very complex. Stanimirova et al. geographically defined Corsican honeys via their volatile organic chemicals profile with headspace SPME GC ×  GC-TOFMS and statistical pattern recognition techniques as an alternate to traditional pollen examination ( 99  ). Theoretically, their approach could be used to identify cases of intentional honey product mislabeling. Cajka et  al. used essentially the same techniques, analytical and statistical, to divide Ligurian and other non-Ligurian Mediterranean olive oils ( 100  ). The Ligurian oil is a premium product that is relatively  scarce. The authors remarked that while SPME GC/MS produced sufficient marker compounds for chemometric profiling of the oils, GC  ×  GC-TOFMS offered a more comprehensive fingerprint and better mass spectral qualities.  Janssen, Steenbergen, and de Koning reviewed the use of  comprehensive chromatography techniques, including GC ×  GC, for the analysis of edible oils and fats, indicating that GC ×  GC  was well-suited for target compound analysis, group-type separation, and chromatographic fingerprinting ( 101 ). An example of  target-compound analysis was provided by Biedermann and Grob  who used GC ×  GC with FID and MS after HPLC separation to determine mineral oil adulteration in sunflower soil ( 102  ). Lojzova et al. used headspace SPME and compared GC-ion trap MS, GC-TOFMS, and GC ×  GC-TOFMS for the analysis of  13 alkylpyrazines and other volatile compounds in potato chips arising from the Maillard reaction during their production ( 103 ).  While none of the instrumental techniques allowed unequivocal determination of all targeted alkylpyrazines, GC ×  GC-TOFMS was declared superior to the other two because of lower limits of  quantification and enhanced nontarget compound screening capability. Beverage-related studies conducted with GC ×  GC included the trace-level analysis of the potent odorants, 3-alkyl-2-methoxypyrazines, in wine grapes ( 104 ) and the characterization of  Brazilian cachaca ( 105  ), a sugar cane derived liquor that surprisingly is the third most consumed distilled alcoholic beverage in the world (after vodka and soju). Analytical Chemistry, Vol. 82, No. 12, June 15, 2010 

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Because of the increase in sensitivity due to the modulation process, GC ×  GC is appropriate for trace residue analysis in a   variety of food sample types. Hoh et al. demonstrated this with quantification for a variety of halogenated compounds, including PCBs, OCPs, and polybrominated diphenyl ethers (PBDEs), in fish oils, using gel permeation chromatography and a large volume, direct sample-introduction technique with GC × GC TOFMS ( 106  ). They also identified nontarget halogenated natural products, including halogenated 1′-methyl-1,2′-bipyrroles (MBPs), DMBPs, methoxylated PBDEs, polybrominated hexahydroxanthene derivatives, and polybromoindoles in the oils. Even “PCBfree” cod liver oils had PCBs. Ratel and Engel reported a 7-fold increase in benzenenic and halogenated volatiles detected in lamb, milk, and oyster samples analyzed with GC  ×  GC-TOFMS versus GC-quadrupole MS ( 107  ). Humston et al. contributed a piece on cacao bean quality, proposing to identify moisture damage before visible signs of mold on beans, using headspace SPME GC ×  GC-TOFMS and chemometric software ( 108 ). Metabolomics. Metabolomics samples are usually extremely  complex and will show many overlapping peaks, even when analyzed by efficient, high resolution GC, so it is not surprising to see GC ×   GC studies in the literature. In addition to full characterization of samples and possible diagnostic value, biomarker discoveries for diabetes ( 109  ) and organic acidurias in infants ( 110  ) have been facilitated by GC ×  GC-TOFMS. GC × GC-TOFMS was used as a complementary technique to liquid chromatography -tandem quadrupole MS to examine targeted metabolites of a bacterium   Methylobacterium extorquens AM1 grown on two different carbon sources ( 111 ). Mateus et al. used GC  ×  GC with TOFMS to characterize volatile chemicals from 11 species of pine trees ( 112  ). In addition to more traditional GC × GC separations, they showed elegant enantioselective GC ×  GC chromatograms for chiral terpenes that may have importance in insect -host pine relationships. Finally, GC  ×  GC-TOFMS allowed terpenoid profiling of two lines of transgenic  Artemisia annua  L., an important plant in traditional Chinese medicine that contains  Artemisinin, which is used in combination therapies to treat  malaria ( 113 ). Petrochemical. Adam et al. delivered the first report for online supercriticial fluid chromatography (SFC) connected to twin-GC ×   GC-FID and used this sophisticated system for thorough characterization of middle distillates, including the complete separation of saturated and unsaturated compounds ( 114 ). Fischer - Tropsch reaction products, including paraffins, olefins, and oxygenates, were probed using GC ×  GC-TOFMS by Bertoncini et al. ( 115  ). Some of the GC  ×  GC petrochemical contributions are notable for their use of detection systems in addition to, or other than,  TOFMS. Basic and neutral nitrogen speciation and quantification in middle distillates with GC ×  GC and a nitrogen-chemiluminescence detector was accomplished by Adam et al. ( 116  ). A rare use of GC  ×  GC with positive chemical ionization and quadrupole MS, for lower molecular weight fatty alcohol alkoxylate analysis,  yielded much more information than could be obtained by electron ionization MS alone ( 117  ). Historically, the volatility range of GC ×  GC for petroleum applications has been rather limited due to modulator temper4782

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ature and flow limitations, GC column stationary phase temperature limits (more polar phases), and even the press-fit  connectors sometimes used to seal GC  ×  GC columns together. However, Dutriez et al. overcame these hindrances to offer a  high-temperature GC ×  GC analysis of vacuum gas oils up to nC60 ( 118 ). They used a short , wide bore, thin -film (10 m × 0.32 mm ×0.10 µm), high-temperature dimethyl polysiloxane column in the first dimension and a high-temperature stable 50% silphenylene polysilphenylene-siloxane column (0.5 m × 0.10 mm ×0.10 µm) in the second dimension. Unfortunately, there is no mention of the type of connector they used to join these columns, an important consideration given that their GC oven temperature program goes to 370  ° C, a temperature where a press-fit connection rarely survives for any length of time. Interestingly, their modulation period was 20 s, perhaps a  record for the longest second dimension separation in GC × GC, but they determined it was necessary for elution of tetraaromatics within the modulation cycle (penta- and heptaaromatics wrapped around). Benefits of the approach were obtaining boiling point distribution (HT-SimDist) and aromatic family quantification for petroleum fractions. Kohl et al. characterized military fog oil, an exceedingly  complex middle distillate petroleum product used as an obscurant in soldier field training, with several GC ×  GC column setups on FID and TOFMS ( 119  ). Mass spectra and the structure of the GC ×  GC chromatogram, combined with data  mining at the edges of the unresolved complex mixture, allowed the authors to propose a composition for the fog oil. It contains mainly aliphatic compounds ranging from C10 to C30, where naphthenes are the major fraction. Aromatics are high in diversity but low in overall concentration, being purposely  removed in the “newer” oils to reduce toxicity. More specifically, alkanes, cyclohexanes, hexahydroindanes, decalins, adamantanes, bicyclohexanes, alkylbenzenes, indanes, tetrahydronaphthalenes, partially hydrogenated polycyclic aromatic hydrocarbons, biphenyls, dibenzofurans, and dibenzothiophenes  were identified using GC ×   GC-TOFMS. GAS CHROMATOGRAPHY DETECTORS In the biennium 2008 to 2009, many research articles and a   worth reading review describing the advances in gas chromatography were available to the scientific community. The review, updated to 2009 ( 120  ), describes multiple applications of GC and the properties of detectors. This review states that, during this period, the most common GC detector for environmental application was the ion trap-mass spectrometric (ITMS) detector (GCITMS). This GC system demonstrated its capabilities for trace level determination of contaminants in diverse environmental samples. Nanogram per liter concentrations of polybromine compounds in earthworms and triclosan in rivers and coastal water  samples were detected using GC-ITMS. Improvement in GC Detector Techniques.  During this period, different GC available techniques were modified to fit  specific requirements. For instance, two-dimensional gas chromatography (GC ×  GC) was coupled to online combustion isotope ratio mass spectrometry (C-IRMS) to enhance peak capacity and signal in the GC ×   GC system without interference with highprecision carbon isotope analysis in urinary steroid samples ( 121 ). Siegler et al. ( 122  ) increased the selectivity in a comprehensive

three-dimensional gas chromatography-flame ionization detector  (GC-FID) by utilizing an ionic liquid stationary phase column in one dimension. With this modification, the authors reported the resolution of 180 peaks per minute in a 3D diesel sample separation.  The presence of arsine and phosphine in light hydrocarbons at  the part-per-billion level was determined by capillary flow technique and gas chromatography with a dielectric barrier discharge detector  (GC-DBDD) ( 123 ). The method includes a large volume injection, capillary flow technology, and the DBDD operating in argon mode.  The researchers reported that the system needed 4 min for complete analysis and remained reliable for 6 months in continuous operation. In addition, the development of microscale-preparative multidimensional gas chromatography coupled to 2-dimensional nuclear magnetic resonance (MDGC-2D NMR) was proposed to isolate and identify pure volatile compounds from a complex sample ( 124 ). The system was used to isolate geraniol from an essential oil matrix and quantitatively resolved from 15 partially coeluting compounds from the first column.  A new generation of electron capture detection (nonradioactive) with a short, nonpolar and wide-bore column was developed for the analysis of isosorbide dinitrate in human serum ( 125  ). The method was linear between 5 and 50 ng/mL with accuracy of 90% and recovery of 99-108%. Another innovation was the combination of electron ionization mass spectrometry and inductively coupled plasma mass spectrometry (GC-EI-MS/ICPMS) for determining  volatile arsenic compounds formed by fecal microorganisms ( 126  ).  The element sensitivity of the ICPMS and molecular identification by EI-MS allowed for the first time the identification of three arsenic species (methyl-methylthio-ethylthio-arsine (MeAs(SMe)(SEt)), dimethyl-methylseleno-arsine (Me2AsSeMe), and thiobis(dimethylarsine) (Me2As)2S) in environmental samples or  human matrixes.  To overcome some of the disadvantages of current flame photometric detectors for the determination of sulfur and phosphorus in hydrocarbons, a multiple flame photometric detector  (mFPD) was developed (GC-mFPD) ( 127  ). The researchers tested five flames on quenching resistance hydrocarbons and found an improvement of nearly 20-fold relative to a single flame mode and almost 10-fold relative to a dual flame mode. The minimum detectable limits for the mFPD were 4  ×  10-11 g S/s and 3  ×  10-12 g P/s, for sulfur and phosphorus, respectively. In addition, the system maintained about 60% of its original analyte chemiluminescence even under the presence of 100 mL/min of methane flow into the detector, which demonstrate the robustness of the system for quenching resistant hydrocarbons. Silva and co-workers ( 128 ) developed a methodology for the analysis of some alcohols as an alternative to the NIOSH recommended method (Method 1405) for organic vapors detection. The methodology combines gas chromatography separation  with a detector made of an optical fiber sensitized with a thin polymeric film of poly[methyl(3,3,3-trifluoropropyl)siloxane] (PMTFPS). With the GC-OF operating in the visible region (650 nm), nine different alcohols (allyl alcohol, n-propyl alcohol, secbutyl alcohol, isobutyl alcohol, n-butyl alcohol, isoamyl alcohol, methyl isobutyl carbinol, cyclohexanol, and diacetone alcohol) were separated. Results were satisfactory compared to the results obtained using a GC-FID system.

GC Detector Improvement through Software Development. Another approach consisted in the development of a radial basis functional neural network (RBFNN) to model the nonlinear  calibration curves of four hexachlorocyclohexane (HCH) isomers obtained with gas chromatography-electron capture detector (GCECD) ( 129  ). The RBFNN method with logarithm-transform and normalization on the calibration data modeled the nonlinear  calibration curves for the four HCH isomers.  A new algorithm was developed for detecting fragmentation patterns in complex samples such as plant tissues and a new  scheme to examine GC/MS spectra ( 130  ). The technique uses a  metabolite database called KNApSAcK and currently includes 49 165 species-metabolite relations from 24 847 metabolites. Development of GC New Detectors. In addition to modification of current methodologies/equipment, new detectors were developed during this period. Li and co-workers ( 131 ) developed a miniaturized atmospheric pressure dielectric barrier discharge (DBD) to be used as GC detector for the analysis of volatile chlorinated hydrocarbons (VCHCs). The methodology uses chemiluminescence emission from the reaction of DBD-split   VCHCs with luminal solution. This detector is of simple construction and an energy saver, with sensitivity at subnanomole concentrations. Another novelty during this biennium was the use of carbon nanotubes as GC detectors ( 132  ). The methodology is based on the gas sensing capability of carbon nanotubes, particularly in field-effect transistors. A carbon nanotube field-effect  transistor was coupled to a gas chromatographer (GC-NTFET) for the separation of BTEX compounds. The system showed good response for 4 weeks with a detection limit lower than 4  µ g/L. Results from the GC- NTFET were comparable to results obtained  with a GC-FID system. Frank L. Dorman   is an Associate Professor of Biochemistry and   Molecular Biology in the Forensics Science Program at Penn State University. Frank’s research has been in the area of the development of   new capillary column stationary phases through the use of computer  modeling and development of applications for the analysis of environ-  mental and forensic compounds of interest using various GC  × GC, GC, and HPLC techniques. Previously, he was the Director of Technical   Development at Restek Corporation in Bellefonte, PA. He received his  Ph.D. in Analytical Chemistry from the University of Vermont in  Burlington, VT. Prior to joining Restek, Frank was employed by Inchcape Testing Services-Environmental Laboratories in several roles, eventually  becoming Senior Chemist for methods development. Frank also holds the  position of Research Professor at Juniata College in Huntingdon, PA.  Joshua J. Whiting   is a Research Analytical Chemist and head of the  ARD at LECO, Corp. in St. Joseph, MI. Prior to that, he was a Senior   Member of the Technical Staff at Sandia National Laboratories in the  Micro Total Analytical Systems Department. He received his M.S. in chemistry from Wright State University in 2000, and his Ph.D. in analytical chemistry from the University of Michigan in 2004 working   for Professor Richard Sacks. His research interests include development  of portable, low-power, GC systems for rapid detection and identification of analytes of interest utilizing MEMS components.  Jack W. Cochran  is the Director of New Business and Technology for   Restek Corporation after working for LECO Corporation as their Director   for Separation Science for 7 years with their GC- and GC  ×  GC -time-  of-flight mass spectrometers. Formerly, he worked at the Illinois Hazardous Waste Research and Information Center and the U.S. Environmental   Protection Agency in Oklahoma doing analytical method development for  environmentally significant compounds in air, water, sediment, tissue,  soil, and other types of samples. His analytical interests include novel   sample preparation and cleanup methods such as QuEChERS and  dispersive solid phase extraction, GC  ×  GC with new capillary column  stationary phases, time-of-flight mass spectrometry, and vacuum-outlet GC.  Jorge Gardea-Torresdey   is the Richard M. and Frances M. Dudley   Professor of Chemistry in the Department of Chemistry at The University  Analytical Chemistry, Vol. 82, No. 12, June 15, 2010 

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of Texas at El Paso in El Paso, TX. He received his Ph.D. in 1988 at   New Mexico State University in Las Cruces, NM. His research interests include environmental chemistry of hazardous heavy metals and organic compounds, gas chromatography, gas chromatography/mass spectroscopy, atomic absorption and emission spectroscopy, inductively coupled plasma/  mass spectroscopy, X-ray absorption spectroscopy, and investigation of   metal binding to biological systems for remediation of contaminated waters and soils (e.g., phytoremediation) and the study of the fate of nanoparticles in the environment. The scientific contributions of Dr. Gardea have allowed him to receive many honors throughout his professional life. He  just received the 2009 SACNAS Distinguished Scientist of the Year Award.  In 2009, Dr. Gardea was highlighted by prestigious journals including  the December 3, 2009 Issue of   Nature. He has authored or coauthored  over 300 research articles and book chapters. He has taught analytical  chemistry and instrumental analysis at the undergraduate level and  advanced analytical chemistry and environmental chemistry at the  graduate level. He is also currently Editor of the  Journal of Hazardous Materials.

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