Comprehensive gas chromatography with selective detection techniques for screening of environmental pollutants

Nowadays, comprehensive two-dimensional gas chromatography (GC×GC) has been acknowledged as a powerful technique for complex sample analysis. Fundamentals of this technique enhance the understanding of complex sample analysis, and contribute to applications in a wide range of samples such as petroleum products, food flavour, perfume, drugs and environmental samples, etc. Several research groups have attempted to study and understand the key elements of GC×GC (the modulator) to explain the modulation process and its modes of operation. Meanwhile, new nomenclature and definitions comprise one aspect of knowledge in GC×GC fundamental relationships. In this thesis, a new terminology called Modulation Ratio (MR) has been added to the list of GC×GC nomenclature. MR has been proposed to provide chromatographers with appropriate choice of modulation period (PM) when GC×GC experiments are carried out. The results show that MR values of 3 to 4 is the preferred value in GC×GC experiments in order to preserve the separation of solutes achieved in the first dimension. Additionally, new operational methods of targeted and comprehensive modes of GC×GC by using the multi-pass loop modulator were investigated. Both the normal set-up, and two looped segments of the capillary column passing through the LMCS modulator, was compared in performance. Both targeted and comprehensive modes, the straight through column segment type, and the two different loop type modulators, were contrasted in the manner in which they permit isolation of regions of the chromatographic band. Two selective detectors, NPD and µECD, were coupled to the GC×GC system for the analysis of environmental pollutants. In this present work, NPD is the detector of choice for the analysis of nitrogen and phosphorus containing compounds. Thus, the analysis of fungicide residues in vegetable samples using GC×GC-NPD was carried out. The unique capability of the GC×GC presentation to show the degradation of a fungicide (iprodione) was demonstrated in this study. The dual detection arrangement which employed both NPD and ECD as parallel detectors (GC×GC-NPD/µECD) for the analysis of multi-class pesticides containing organochlorine pesticides (OCs), organophosphorus pesticdes (OPs) and fungicides (FCs) was conducted. Two deactivated fused silica transfer lines with an equal split ratio connected the output of the second dimension column (2D) via a microfluidic-splitting valve resulted in two simultaneous contour plots visualized from this system. In this context, an opportunity is shown for assigning a detector response ratio (DRR) with the simultaneous response of a solute in the two detectors, as an additional confirmation of solute identity. Likewise, the application of GC×GC-µECD system for the analysis of PCB congeners was performed. The group separation of PCB congeners was achieved with the optimum GC×GC condition. To illustrate the potential of GC×GC-µECD technique as a powerful tool for conducting a group separation of PCB congeners, highly contaminated soil samples were investigated

Dual NPD/ECD detection in comprehensive two-dimensional gas chromatography for multiclass pesticide analysis

A comprehensive 2-D GC (GC x GC) dual detection system, coupled to nitrogen-phosphorus detection (NPD) and electron capture detection (ECD) has been developed for multiclass pesticide analysis in vegetable sample matrices. The second dimension column was connected to the parallel detectors via a microfluidic splitting device. The sample set comprised 17 organochlorine pesticides, 15 organophosphorus insecticides and 9 N-containing fungicides. Selective detection of vegetable sample extracts provides increased information content through simultaneous, correlated GC x GC plots for both ECD and NPD, which demonstrated improved separation of pesticide standards from each other, and from the sample matrix. The efficiency of NPD and ECD modes was investigated and compared; the ECD produced broader peaks, with the ECD generating greater response as measured by S/N ratio. Accuracy and precision of the approach were determined as repeatability and reproducibility for selected pesticides. The RSDs of the intraday (n = 5) and interday (3 days) analyses of the selected pesticides are less than 2.5 and 10%, respectively. The relative ratio of the ECD/NPD response is proposed to offer additional identification of individual pesticides, in addition to the (1)t(R) and (2)t(R) retention coordinates; ratios vary from 19 to over 1000 for selected pesticides that also exhibit ECD and NPD activities

Application of comprehensive two-dimensional gas chromatography with nitrogen-selective detection for the analysis of fungicide residues in vegetable samples

Comprehensive two-dimensional gas chromatography (GCxGC) with nitrogen-phosphorus detection (NPD) has been investigated for the separation and quantitation of fungicides in vegetable samples. The detector gas flows (H-2, N-2 and air) were adjusted to achieve maximum response of signal whilst minimizing peak width. The comparison of different column sets and selection of the temperature program were carried out with a mixture of nine N-containing standard fungicides, eight of which were chlorinated. The results from GCxGC-NPD and GCxGC with micro electron-capture detection (mu ECD) were compared. External calibrations of fungicides were performed over a concentration range from I to 1000 mu g L-1. The peak area calibration curves generally had regression coefficients of R-2 > 0.9980, however for iprodione which was observed to undergo on-column degradation, an R-2 of 0.990 was found. The limit of detection (LOD) and limit of quantitation (LOQ) were less than about 74 and 246 ng L-1, respectively. The intra-day and inter-day RSD values were measured for solutions of concentration 0.100, 0.500 and 1.50 mg L-1. For the 0.500 mg L-1 solution, intra- and inter-day precision of peak area and peak height for most of the pesticides were about 2% and 8%, respectively. Excellent linearity was observed for these standards, from 0.001 to 25.00 mg L-1. The standard mixture peak positions were identified by using GCxGC with quadrupole mass spectrometry (qMS). To illustrate the potential and the versatility of both GCxGC-NPD and GCxGC-mu ECD, the method was applied to determination of fungicides in a vegetable extract. Decomposition of one fungicide standard (iprodione) during chromatography elation was readily observed in the two-dimensional (2D) GCxGC plot as a diagonal ridge response in the 2D chromatogram between the degrading compound and the decomposition product

Peak modeling approach to accurate assignment of first-dimension retention times in comprehensive two-dimensional chromatography

Modeling of first-dimension retention of peaks based on modulation phase and period allows reliable prediction of the modulated peak distributions generated in the comprehensive two-dimensional chromatography experiment. By application of the inverse process, it is also possible to use the profile of the modulated peaks (their heights or areas) to predict the shape and parameters of the original input chromatographic band (retention time, standard deviation, area) for the primary column dimension. This allows an accurate derivation of the firstdimension retention time (RSD 0.02%) which is equal to that for the non-modulated experiment, rather than relying upon the retention time of the major modulated peak generated by the modulation process (RSD 0.16%). The latter metric can produce a retention time that differs by at least the modulation period employed in the experiment, which displays a discontinuity in the retention time vs modulation phase plot at the point of the 180&deg; out-ofphase modulation. In contrast, the new procedure proposed here gives a result that is essentially independent of modulation phase and period. This permits an accurate value to be assigned to the first-dimension retention. The proposed metric accounts for the time on the seconddimension, the phase of the distribution, and the holdup time that the sampled solute is retained in the modulating interface. The approach may also be based on the largest three modulated peaks, rather than all modulated peaks. This simplifies the task of assigning the retention time with little loss of precision in band standard deviation or retention time, provided that these peaks are not all overloaded in the first or second dimension.<br /

Metabotyping of human colorectal cancer using two-dimensional gas chromatography mass spectrometry

10.1007/s00216-012-5870-5Analytical and Bioanalytical Chemistry4032483-493ABCN