Single-column Gas Chromatography Research Articles

A Single-Column Gas Chromatography Method for Quantifying Toxic Alcohols.

Rapid identification and quantification of toxic alcohols and ethylene glycol is imperative for appropriate treatment. Clinical laboratories frequently rely on direct injection gas chromatography (GC) methods, but these methods require inlet maintenance and multiple GC systems. To overcome these challenges, we developed a single-column headspace GC method for both toxic alcohols and glycols that streamlines patient sample analysis for toxic alcohol ingestion. Optimal parameters for nonderivatized (volatile) and derivatized (glycol) plasma samples were determined using a 7890 A headspace sampler, an Agilent 7697 A GC system, a DB-200 column, and a flame ionization detector. Limit of Quantification (LoQ), linearity, imprecision, carry-over, method comparison, and interference studies were performed using quality control materials and prepared plasma samples. Our volatile method is linear to 3000 mg/L (ethanol) with LoQ concentrations below 20 mg/L (ethanol). The glycol method is linear to 2000 mg/L (ethylene glycol) with LoQ concentrations below 40 mg/L (ethylene glycol). Total assay impression ranged from 1.7% for ethanol to 13.3% for propylene glycol. Both methods were free of sample carryover and compared favorably with a similar clinical method at an outside laboratory. Propionic acid, an accumulating metabolite in methylmalonic acidemia that interferes with ethylene glycol identification by a different method, did not interfere with the ethylene glycol method reported here. Our single-column headspace GC method provides reliable, robust, and rapid identification and quantification of commonly encountered toxic alcohols. Clinical laboratories relying on direct injection Gas Chromatography (GC) for toxic alcohol analysis face challenges including frequent inlet maintenance, sample carryover, or the need for separate GC systems for volatile and glycol analysis. We summarize our development and optimization of two headspace GC methods for nonderivatized (volatile) and derivatized (glycol) plasma samples that use a single DB-200 analytical column. These methods are comparable to other GC methods, not prone to sample carryover, eliminate the need for multiple GC systems or columns, and are readily applicable to other laboratories that provide toxic alcohol analysis.

The Application of a Single-Column GC-MS-MS Method for the Rapid Analysis of Chemical Warfare Agents and Breakdown Products.

The development of one comprehensive gas chromatographic-triple quadrupole mass spectrometric (GC-MS-MS) method for the analysis of nerve agents and their breakdown products can pose a challenge due to significant differences in analyte volatility. Nerve agent breakdown products typically have a low volatility, requiring a derivatization step prior to analysis by gas chromatography (GC). However, nerve agent parent compounds are generally more volatile, which eliminates the need for derivatization and allows for direct analysis. Therefore, the analysis of these analytes is typically performed using separate analytical methods. This may require the use of multiple columns composed of different stationary phases to ensure the most efficient separation. With the wide selection of GC columns and derivatizing agents, it is potentially possible to develop a single-column/analytical method that is suitable for the detection of nerve agents and their breakdown products. We evaluated six nerve agents (tabun, sarin, soman, cyclosarin, VX and Russian VX) and the six corresponding breakdown products (EDPA, IMPA, PMPA, CMPA EMPA and MMPA). Chromatographic separation and multiple-reaction mode electron ionization detection of the nerve agents and silylated breakdown product derivatives were performed using an Agilent 7890 A gas chromatography (GC) equipped with a mid-polarity column, coupled to a 7000 triple quadrupole mass spectrometry system. A fast (12.5 min), highly sensitive (picogram) and selective method was achieved. The feasibility of this method for nerve agent and breakdown product detection in real samples was demonstrated using nerve agent-spiked human plasma at various exposure times (3 min, 1 h and 24 h). Five of the six nerve agents and all six breakdown products were successfully detected. This robust method has utility as a rapid screening tool to identify a specific nerve agent in a potential exposure event by simultaneous detection of the parent and or its corresponding breakdown product in plasma.

Analysis of polychlorodibenzo-p-dioxins and polychlorodibenzofurans in stationary source emissions in GC-MS/MS using hydrogen as the carrier gas.

The European and American methods for the determination of polychlorodibenzo-p-dioxins and polychlorodibenzofurans in stationary source emissions require a high-resolution mass spectrometer detector. At the same time, all of the 17 toxic 2,3,7,8-chlorine-substituted isomers have to be separated by an appropriate chromatographic method. The resulting analysis has long runtimes and sometimes a double-column run is needed, which results in a huge waste of time, money and manual labor. To obtain a fast and cost-effective but still reliable analytical system, a single-column gas chromatography with hydrogen as carrier gas and tandem mass spectrometry detection is proposed. The use of hydrogen as the carrier gas is a good choice to shorten runtimes and improve the chromatographic resolution, while tandem mass spectrometry is a well-known alternative for this analysis. All the chromatographic and mass spectrometric parameters fill the requirements of the reference methods with a 35% reduction of runtimes. The accuracy is tested with three fly ash samples of a proficiency interlaboratory test. A good correlation between the results is obtained (R2 =0.992, slope=0.9675), and no coelutions are noted. The system robustness is tested during 5 years of constant use and the maximal relative standard deviation of the relative response factor is 18.8%.

Beef, chicken and lamb fatty acid analysis — a simplified direct bimethylation procedure using freeze-dried material

When fractionation of meat lipids is not required, procedures such as saponification can be used to extract total fatty acids, reducing reliance on toxic organic compounds. However, saponification of muscle fatty acids is laborious, and requires extended heating times, and a second methylation step to convert the extracted fatty acids to fatty acid methyl esters prior to gas chromatography. Therefore the development of a more rapid direct methylation procedure would be of merit. The use of freeze-dried material for analysis is common and allows for greater homogenisation of the sample. The present study investigated the potential of using freeze-dried muscle samples and a direct bimethylation to analyse total fatty acids of meat (beef, chicken and lamb) in comparison with a saponification procedure followed by bimethylation. Both methods compared favourably for all major fatty acids measured. There was a minor difference in relation to the C18:1 trans 10 isomer with a greater (P<0.05) recovery with saponification. However, numerically the difference was small and likely as a result of approaching the limits of isomer identification by single column gas chromatography. Differences (P<0.001) between species were found for all fatty acids measured with no interaction effects. The described technique offers a simplified, quick and reliable alternative to saponification to analyse total fatty acids from muscle samples.

Determination of Seven Nitrobenzene Compounds in Mainstream Cigarette Smoke with Heart-Cutting Two-Dimensional Gas Chromatography

A heart-cutting two-dimensional gas chromatography (GC) method was developed for the determination of nitrobenzene compounds (NBCs) in mainstream cigarette smoke. For the method, the particulate matter of cigarette smoke was extracted with cyclohexane, purified with a silica solid-phase extraction (SPE) cartridge and analyzed by heart-cutting two-dimensional GC equipped with two electron capture detectors. The heart-cutting two-dimensional GC was achieved by a single-column GC oven equipped with a microfluidic pressure balanced device (Deans switch). Two-dimensional GC was compared to single-dimensional GC and found to be clearly better for the separation of seven NBCs from a complex smoke matrix. The limits of detection ranged from 1.28 to 9.83 ng/mL, spiked recoveries were between 88.3 and 106.8% and relative standard deviation ranged from 2.79 to 12.78%. The NBCs yields of six kinds of Chinese and international cigarettes brands, which were all smoked according to two smoking protocols (International Organization for Standardization and Health Canada Intense smoking regimens), were determined and compared.

Model for predicting comprehensive two-dimensional gas chromatography retention times

A model for approximating the relative retention of solutes in comprehensive two-dimensional gas chromatography (GC × GC) is presented. The model uses retention data from standard single-column temperature-programmed separations. The one-dimensional retention times are first converted into retention indices and then these indices are combined in a simple manner to generate a retention diagram. A retention diagram is an approximation of the two-dimensional chromatogram that has retention order and spacing in both dimensions similar to that found in the experimental chromatogram. If required, the retention diagram can be scaled to more closely resemble the two-dimensional chromatogram. The model has been tested by using retention time data from single-column gas chromatography–mass spectrometry and valve-based GC × GC. A total of 139 volatile organic compounds (VOCs) were examined. Approximately half of the VOCs had a single functional group and a linear alkyl chain (i.e., compounds with the structure Z (CH 2) n H). The retention diagrams had primary retention orders that were in excellent agreement with the GC × GC chromatograms. The relative secondary retention order for compounds with similar structures was also accurately predicted by the retention diagram. However, the relative secondary retention for compounds with dissimilar structures, such as acyclic alcohols and multi-substituted alkylbenzenes, were less accurately modeled. This study demonstrates how readily available single-column retention time data can be used to provide an a priori estimate of the relative retention of solutes in a GC × GC chromatogram. Such a capability is useful for screening possible combinations of stationary phases.

Comprehensive two-dimensional gas chromatography in combination with rapid scanning quadrupole mass spectrometry in perfume analysis

Single column gas chromatography (GC) in combination with a flame ionization detector (FID) and/or a mass spectrometer is routinely employed in the determination of perfume profiles. The latter are to be considered medium to highly complex matrices and, as such, can only be partially separated even on long capillaries. Inevitably, several monodimensional peaks are the result of two or more overlapping components, often hindering reliable identification and quantitation. The present investigation is based on the use of a comprehensive GC (GC × GC) method, in vacuum outlet conditions, for the near to complete resolution of a complex perfume sample. A rapid scanning quadrupole mass spectrometry (qMS) system, employed for the assignment of GC × GC peaks, supplied high quality mass spectra. The validity of the three-dimensional (3D) GC × GC–qMS application was measured and compared to that of GC–qMS analysis on the same matrix. Peak identification, in all applications, was achieved through MS spectra library matching and the interactive use of linear retention indices (LRI).

A Model of Peak Amplitude Enhancement in Orthogonal Two-Dimensional Gas Chromatography

Increases in peak capacity that are achieved using comprehensive rather than single-column gas chromatography are also often accompanied by significant improvements in minimum detectable amounts. Comprehensive gas chromatography utilizes a zone compression of eluent between primary and secondary chromatography columns, with complete conservation of mass. In this paper, we present a theoretical model of peak amplitude enhancement based on translation of the fractional area under the primary column normal curve to a secondary Gaussian peak. Amplitude enhancement made by peak modulation scales with increasing modulation period and primary column peak width. An exponential relationship between the modulated secondary column peak width and the amplitude enhancement is also observed. The calculated amplitude gains are further corrected for detector current noise generated via flame ionization detection at a range of operating frequencies. An example of trace level atmospheric analysis is used to demonstrate both peak capacity and sensitivity enhancements using the multidimensional technique.

Identification of furan fatty acids in human blood cells and plasma by multi-dimensional gas chromatography-mass spectrometry

The separation and determination of low-concentration furan fatty acids in complex sample matrices, such as oils, tissue lipids or blood, previously required time-consuming pre-analytical separation steps in order to obtain sufficient resolution in single-column gas chromatography. By using a multi-dimensional GC-MS system, it is now possible to identify directly the methyl esters of furan fatty acids without any further pre-analytical separations. The Folch method was used to isolate the lipids from the different blood components and transesterification of total lipids was carried out by sequential saponification and esterification. Individual lipid classes were isolated by preparative TLC separation and transesterified into their methyl esters by a one-step reaction using acetyl chloride as catalyst. Furan fatty acids were found in all blood samples in differing relative amounts. 12,15-Expoxy-13,14-dimethyleicosa-12,14-dienoic acid (F6) and 12,15-epoxy-13,14-dimethyloctadeca-12,14-dienoic acid (F4) were detected in both red blood cells and in plasma; in platelets, only F6 was found. In serum, furan fatty acids were detected only in the phospholipid fraction, and not in cholesterol esters or triglycerides.

Simplex optimization of the analysis of polychlorinated biphenyls: Application to the resolution of a complex mixture of congeners of interest on a single gas chromatographic column

The modified sequential simplex method was applied to optimize the oven temperature programming of a single-column gas chromatography procedure developed to determine polychlorinated biphenyl congeners in a mixture of technical Aroclors. Both the overall resolution of fourteen congeners of interest and the time of analysis were taken into account in the optimization. Successful seperations of some clusters usually unresolved with a single column have been obtained.