Quantitative aspects in comprehensive two-dimensional gas chromatography

Selective and comprehensive analysis of organohalogen compounds by GC × GC-HRTofMS and MS/MS

Thousands of organohalogen compounds, including hazardous chemicals such as polychlorinated biphenyls (PCBs) and other persistent organic pollutants (POPs), were selectively and simultaneously detected and identified with simple, or no, purification from environmental sample extracts by using several advanced methods. The methods used were software extraction from two-dimensional gas chromatography-high-resolution time-of-flight mass spectrometry (GC × GC-HRTofMS) data, measurement by negative chemical ionization with HRTofMS, and neutral loss scanning (NLS) with GC × GC-MS/MS. Global and selective detection of organochlorines and bromines in environmental samples such as sediments and fly ash was achieved by NLS using GC × GC-MS/MS (QQQ), with the expected losses of ³⁵Cl and ⁷⁹Br. We confirmed that negative chemical ionization was effective for sensitive and selective ionization of organohalogens, even using GC × GC-HRTofMS. The 2D total ion chromatograms obtained by using negative chemical ionization and selective extraction of organohalogens using original software from data measured by electron impact ionization were very similar; the software thus functioned well to extract organohalogens. Combining measurements made by using these different methods will help to detect organohalogens selectively and globally. However, to compare the data obtained by individual measurements, the retention times of the peaks on the 2D chromatograms need to match.

Fully Automated Portable Comprehensive 2-Dimensional Gas Chromatography Device

We developed a fully automated portable 2-dimensional (2-D) gas chromatography (GC x GC) device, which had a dimension of 60 cm × 50 cm × 10 cm and weight less than 5 kg. The device incorporated a micropreconcentrator/injector, commercial columns, micro-Deans switches, microthermal injectors, microphotoionization detectors, data acquisition cards, and power supplies, as well as computer control and user interface. It employed multiple channels (4 channels) in the second dimension (²D) to increase the ²D separation time (up to 32 s) and hence ²D peak capacity. In addition, a nondestructive flow-through vapor detector was installed at the end of the ¹D column to monitor the eluent from ¹D and assist in reconstructing ¹D elution peaks. With the information obtained jointly from the ¹D and ²D detectors, ¹D elution peaks could be reconstructed with significantly improved ¹D resolution. In this Article, we first discuss the details of the system operating principle and the algorithm to reconstruct ¹D elution peaks, followed by the description and characterization of each component. Finally, 2-D separation of 50 analytes, including alkane (C₆-C₁₂), alkene, alcohol, aldehyde, ketone, cycloalkane, and aromatic hydrocarbon, in 14 min is demonstrated, showing the peak capacity of 430-530 and the peak capacity production of 40-80/min.

Pixel-based analysis of comprehensive two-dimensional gas chromatograms (color plots) of petroleum: a tutorial

We demonstrate how to process comprehensive two-dimensional gas chromatograms (GC × GC chromatograms) to remove nonsample information (artifacts), including background and retention time shifts. We also demonstrate how this, combined with further reduction of the influence of irrelevant information, allows for data analysis without integration or peak deconvolution (pixel-based analysis).

Analytical method of free and conjugated neutral aroma components in tobacco by solvent extraction coupled with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

A reliable and simple method for quantitative analysis of free and conjugated neutral aroma components (including aldehydes, ketones, alcohols, esters and alkenes) in tobacco using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) is described. Simple solvent extraction using methyl tert-butyl ether (MTBE) ensured extraction of the neutral aroma components in their free form. The components present as conjugates were isolated using MTBE extraction following acid-catalysed hydrolysis. The GC × GC-TOFMS analysis was performed to comprehensively identify different forms of neutral aroma components in tobacco. Compared with the conventional methods, our method not only simplified the process but also saved time and solvent. It also exhibited higher selectivity and sensitivity and demonstrated the following results: the limit of detection of the neutral aroma components varied from 0.006 μg/g for 2-acetylfuran to 0.133 μg/g for 5-(hydroxymethyl)-2-furfural, the relative standard deviations were from 0.5% to 6.8% and the recovery ranged from 82.4% to 118.2%. The optimized method was successfully employed to analyse real tobacco samples. Eighty-three neutral aroma components of interest were identified.

Evaluation of comprehensive two-dimensional gas chromatography-time-of-flight-mass spectrometry for the analysis of polycyclic aromatic hydrocarbons in sediments

This study evaluates the feasibility of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-ToF MS) for the determination of the 15+1 EU PAHs in sediments. Experimental variables affecting the injection, chromatographic separation and analytical detection of the analytes have systematically been optimised. Under finally proposed conditions, a satisfactory resolution among critical pairs/groups of PAHs, including benz[a]anthracene, cyclopenta[cd]pyrene and chrysene, the three benzofluoranthene isomers, indeno[1,2,3-cd]pyrene from dibenz[a,h]anthracene (DahA), and DahA from dibenz[a,c]anthracene, has been achieved using DB-5 × BPX-50 as column combination with a run time of 1 h. The feasibility of the method for the analysis of real-life samples has been demonstrated by accurate determination of relevant target PAHs in the certified harbour sediment BCR-535 (deviations among certified concentration values and those calculated using the proposed method lower than 3%); and by successful application to sediments sampled from a relevant protected area located in the South of Spain. The low methodological limits of detection (LODs) obtained for most of the targeted PAHs (in the 5.7-60 μg/kg range, as calculated for real samples) guarantied accurate quantification of the target compounds at the low levels expected in these types of pristine matrices. The strong retention experienced by the heaviest dibenzopyrene isomers included in the study resulted in relatively high LODs for these analytes; nevertheless, these compounds were detected at concentration levels above the corresponding LOD in some of the analysed sediments. In addition, the enhanced identification power provided by GC × GC-ToF MS for the identification of non-target analytes allowed the tentative identification of a group of polynuclear aromatic thiophenes in some of the test samples. Finally, the potential of the use of normalised bubble plots for the fast screening of the potential PAH sources has been demonstrated.