Novel molecular materials and computational strategies with gas chromatography

The ability to detect, identify and quantify many types of compounds in complex matrices is paramount for many disciplines and application areas such as proteomics, environmental, pharmaceutical, medical, petrochemical, food and beverages. Existing detection technologies, such as high resolution mass spectroscopy, may fail to adequately analyse compounds of interest in multi‐component samples; isomers or compound identity may be incorrectly reported, e.g. false positive identification of illicit drugs, biomarkers or synthetic compounds due to the presence of interferences or by‐products. Chromatographic methods offer an effective solution where target analytes in complex matrices are separated from the non‐targets allowing improved identification of many compounds with minimised signal interference in a single analysis. Identification and quantification of well separated isomers can also be achieved. Among different separation techniques, comprehensive two dimensional gas chromatography (GC×GC) has been realised as a high resolution analysis technique allowing the separation of hundreds of analytes based on their differing boiling points and/or polarities. A simple concept may be that components in samples should be separated as much as possible, permitting unambiguous analysis of target analytes in GC×GC. Within this simple concept, a tremendous amount of time, consumables and energy needs to be spent on the optimisation process since the GC×GC method incorporates two dissimilar column geometries, and choice of stationary phases leading to many variables that must be considered when performing separation such as relative column dimensions, types of stationary phases, temperature programs and carrier gas flow. Thousands of experiments may need to be performed in order to obtain an effective chromatographic outcome for each sample. Understanding the impact of these variables on separation mechanisms is thus important to design an effective optimisation processes, and to reduce valuable resources. Recently, there has been an increasing interest in developing new methodologies for improved GC×GC analysis, utilising novel materials such as ionic liquids (IL) as stationary phases with high polarity and good thermal stability. Besides the polar/nonpolar interactions, additional hydrogen bond basicity is also obtained with these phases, due to the customisable functionalities of IL allowing introduction of acid moieties onto the IL stationary phase molecules which broadens selectivity in GC and finally offers improved overall separation quality (orthogonality) in GC×GC. In this thesis, new theoretical concepts and approaches to direct column selection and to aid optimisation of experimental conditions in GC×GC were established according to linear solvation energy relationship (LSER) and molecular modelling. Relevant computational software was developed according to the established approaches in order to simulate GC×GC results for individual experimental investigation covering a wide range of compounds such as fatty acid methyl esters, hydrocarbons in petroleum, alcohols, aldehydes, terpenes, polychlorinated naphthalenes and polychlorinated biphenyls. These simulated results were evaluated by comparison with experimental results. The theories, methods and results presented in this thesis will, in the future, allow further targeted developments of novel experimental design, effective stationary phase material selection, an understanding of separation mechanisms with IL stationary phases in GC×GC, and the possibility to design tuned stationary phases that further improve separation performance. These principles could also equally well apply to heart‐cut multidimensional GC operation

Solid phase microextraction for quantitative analysis – Expectations beyond design?

Solid phase microextraction (SPME) is a convenient, effective and green sample preparation technique, offering excellent compatibility with different chromatography methods. This review presents an overview of the history of the SPME technique and its early adaptation based on reported patents, followed by some current SPME designs, and intended usage, especially for gas chromatography (GC) applications. Particular focus on quantification approaches in SPME is included, with emphases on the methodology chosen for implementation, correct performance of quantification and validation, and the calibration method. The article concludes by highlighting some innovative SPME-related techniques, some of which are chosen for their quantitative coverage of analytes and their reported applications

In Silico Modeling of Hundred Thousand Experiments for Effective Selection of Ionic Liquid Phase Combinations in Comprehensive Two-Dimensional Gas Chromatography

The selection of the best column sets is one of the most tedious processes in comprehensive two-dimensional gas chromatography (GC × GC) where a multitude of choices of column sets could be employed for an individual sample analysis. We demonstrate analyte/stationary phase dependent selection approaches based on the linear solvation energy relationship (LSER), which is a reliable concept for the study of interaction mechanisms and retention prediction with a large database pool of columns and compounds. Good correlations between our predicted results, with experimental results reported in the literature, were obtained. The developed approaches were applied to the simulation of 157 920 individual experiments in GC × GC, focusing on the application of 30 nonionic liquid and 111 ionic liquid (IL) stationary phases for separation of some example sets of model compounds present in practical samples. The best column sets for each sample separation could then be extracted according to maximizing orthogonality, which estimates the quality of separation

Thermally Sensitive Behavior Explanation for Unusual Orthogonality Observed in Comprehensive Two-Dimensional Gas Chromatography Comprising a Single Ionic Liquid Stationary Phase

In this study, a theoretical concept and method to achieve a degree of orthogonality in comprehensive two-dimensional gas chromatography (GC × GC) for separation of fatty acid methyl esters (FAME) by using a single ionic liquid (IL) stationary phase (1-phase-GC × GC) were established. The 1-phase system comprises a long IL column and shorter IL column of the same phase before and after the modulation region, operated under temperature-programmed conditions. Initial isothermal experiments employing six commercial IL columns were conducted at different temperatures. On the basis of the temperature-dependent linear solvation energy relationship (LSER) concept, SLB-IL111 exhibited the greatest thermal sensitivity and degree of difference over the tested temperature (<i>T</i>) range, so it was selected for investigation of the 1-phase-GC × GC mode. With the same temperature program, a significantly high degree of orthogonality was observed for the experiment, varied with column lengths. The switchable separation result, which inverts the retention of saturated and unsaturated FAME on the downstream column (²D), was achieved by varying column diameters and surface thicknesses of the IL-coated layers. These results were explained according to the corresponding LSER principles. Also, the time summation model was applied for the simulation of the observed 1-phase-GC × GC results

Person-portable gas chromatography-toroidal ion trap mass spectrometry analysis of coffee bean volatile organic compounds

Analysis of roasted coffee bean volatile organic compounds (VOCs) was performed using person-portable gas chromatography-toroidal ion trap mass spectrometry (ppGC-TMS). Chromatographic separation performance and mass spectra were compared and contrasted with benchtop gas chromatography-quadrupole time-of-flight mass spectrometry (GC-QTOFMS) and gas chromatography-quadrupole mass spectrometry (GC-QMS). The tentative identification of about 50 analytes was established in benchtop analysis, based on accurate MS data, MS spectrum matching and retention indices, and con-trasted with 20 individual analyte peaks similarly recognised in ppGC-TMS analysis. This study suggests the suitability of ppGC-TMS analysis for rapid coffee VOC profiling with minimal sample preparation, using selective key chemical markers, with potential use for on-site process monitoring and roasting optimisation.(c) 2022 Elsevier B.V. All rights reserved