Lena Martina Dubois

In this review, we consider and discuss the affinity and complementarity between a generic sample preparation technique and the comprehensive two‐dimensional gas chromatography process. From the initial technical development focus (e.g., on the GC×GC and solid‐phase microextraction techniques), the trend is inevitably shifting toward more applied challenges, and therefore the preparation of the sample should be carefully considered in any GC×GC separation for an overreaching research. We highlight recent biomedical, food and plant applications (2016‐July 2020), and specifically those in which the combination of tailored sample preparation methods and GC×GC‐MS has proven to be beneficial in the challenging aspects of non‐targeted analysis. Specifically on the sample preparation, we report on gas‐phase, solid‐phase, liquid‐phase extractions, and derivatization procedures that have been used to extract and prepare volatile and semi‐volatile metabolites for the successive GC×GC analysis. Moreover, we also present a milestone section reporting the early works which pioneered the combination of sample preparation techniques with GC×GC for non‐targeted analysis. This article is protected by copyright. All rights reserved

The present research reports on the development of a methodology to unravel the complex phytochemistry of cannabis. Specifically, cannabis inflorescences were considered and stir bar sorptive extraction (SBSE) was used for pre-concentration of the metabolites. Analytes were thermally-desorbed into a comprehensive two-dimensional gas chromatography (GC×GC) system coupled with low- and high-resolution mass spectrometry (MS). Particular attention was devoted to the optimization of the extraction conditions to extend the analytes’ coverage, and to the optimization of the chromatographic separation to obtain a robust dataset for further untargeted analysis. Monoterpenes, sesquiterpenes, hydrocarbons, cannabinoids, other terpenoids, and fatty acids were considered to optimize the extraction conditions. The response of selected ions for each chemical class, delimited in specific 2D chromatographic regions, enabled an accurate and fast evaluation of the extraction variables (i.e., time, temperature, solvent, salt addition), which were then selected to have a wide analyte selection and good reproducibility. Under optimized SBSE conditions, eight different cannabis inflorescences, and a quality control sample were analyzed and processed following an untargeted and unsupervised approach. Principal component analysis on all detected metabolites revealed chemical differences among the sample types which could be associated with the plant subspecies. With the same SBSE-GC×GC-MS methodology, a quantitative targeted analysis was performed on three common cannabinoids, namely delta-9-tetrahydrocannabinol, cannabidiol, and cannabinol. The method was validated, giving correlation fac-tors over 0.993, and <12% reproducibility (relative standard deviation) at the lowest calibration point. The high-resolution MS acquisition allowed for high confidence identification and post-targeted analysis, confirming the presence of two pesticides, a plasticizer, and a cannabidiol degradation product in some of the samples.

After its introduction in the early 1990’s, comprehensive two-dimensional gas chromatography (GC×GC) has evolved from a separation science research tool to the central component of many industries. Despite the maturity of the technique, some fields remain reluctant to its use in routine applications. In the case of forensic science, some constraints are the strict requirements enforced in forensic laboratories and the time and effort that must be invested for intra-laboratory method validation. Concerns may also arise about whether information could be lost when transitioning to a new technique. This study reports on a method translation from conventional one-dimensional (1D) GC to GC×GC, ensuring the integrity of data as conversion is made. The GC was retrofitted with a reverse fill/flush (RFF) flow modulator and equipped with dual channel detection using a quadrupole mass spectrometer (qMS) and a flame ionization detector (FID). The parallel use of two detectors, where qMS was applied for qualitative identification and FID for quantification, allowed higher flows and slightly wider peaks to be exploited for the analysis of a volatile organic compound (VOC) reference mixture relevant to forensic VOC profiling. Peak quality assessment and calibration curves using GC-qMS and GC×GC-qMS/FID document the transfer and adaptation of the original method without a loss in data quality. Furthermore, the pre-processing and the data analysis pro-cessing steps, including calibration and peak quality assessment for each of the three datasets, are explained in detail. This information provides benchmark data for routine laboratories that want to implement a GC×GC approach into routine workflows.

Headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) have traditionally been used, in combination with other analyses, for the chemical characterization of organic residues recovered from archaeological specimens. Recently in many life science fields, comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) has provided numerous benefits over GC-MS. This study represents the first use of HS-SPME-GC×GC-TOFMS to characterize specimens from an experimental modern reference collection. Solvent extractions and direct analyses were performed on materials such as ivory, bone, antlers, animal tissue, human tissue, sediment, and resin. Thicker film column sets were preferred due to reduced column overloading. The samples analyzed by HS-SPME directly on a specimen appeared to give unique signatures and generally produced a higher response than for the solvent-extracted residues. A non-destructive screening approach of specimens may, therefore, be possible. Resin and beeswax mixtures prepared by heating for different lengths of time appeared to provide distinctly different volatile signatures, suggesting that GC×GC-TOFMS may be capable of differentiating alterations to resin in future studies. Further development of GC×GC-TOFMS methods for archaeological applications will provide a valuable tool to uncover significant information on prehistoric technological changes and cultural behavior.