Reproducibility of Programmed-Temperature Retention Indices under Average Linear Velocity Carrier Gas Control of GC and GC–MS

Comprehensive study of retention influencing gas chromatographic parameters affecting linear retention indices

Retention in gas chromatographic systems has a central role in the identification of compounds even if detectors providing spectral information are used. But linear retention indices (LRI) of a single compound originating from multiple sources tend to vary greatly, probably due to differences in the experimental settings of the determinations. The effect of gas chromatographic parameters on LRI has been investigated using 41 compounds - previously identified from food contact plastics - and n-alkanes (n-C7-n-C40) used as reference series. As the reproducibility of LRIs under the same conditions is generally very good, the smallest changes in the settings often caused statistically significant, though irrelevant changes in the LRI values. Therefore, a multicriterial scoring-ranking system has been worked out to highlight the LRI value differences. Our results highlight that column length, heating rate, and film thickness can all be the reasons of the varying published LRI values. We also demonstrated that for the reproduction of LRI data, the chemistry (and not simply the polarity) of the stationary phase is crucial.

Development and validation of analytical method for identification of new psychoactive substances using linear retention indexes and gas chromatography-mass spectrometry

New Psychoactive Substances (NPS) are quickly developing to evade legislation, posing unprecedented challenges to public health and law enforcement authorities around the world. The aim of this work was to develop and validate a simple and reliable non-target gas chromatography/mass spectrometry (GC/MS) analytical method based on linear retention indexes for the expeditious identification of NPS without the need of analytical standards. The method was optimized and validated for 22 different drugs covering ten categories: phenethylamines (amphetamine, MDMA, methamphetamine, 25CNBOMe, 2-FA, 5-MAPB), "classic" drugs (cocaine, ephedrine, THC, heroine), synthetic cannabinoids (JWH-081, AM-2201, JWH-210, MAM-2201), piperazines (o-CPP, p-CPP), tryptamines (5-MeO-MiPT), synthetic cathinones (N-ethylpentylone), synthetic opioids (U-47700), aminoindanes (5-IAI), plant-based substances (Salvinorin-A) and "other" (methiopropamine). Three figures of merit (Selectivity, Precision and Robustness) were evaluated with retention index confidence intervals ranging from 0.5 to 20.6 i.u. and relative standard deviations in the range of 0.003% to 0.027% (repeatability) and 0.02% to 0.29% (intermediate precision). A general equation for estimating linear retention index variation as a function of retention time tolerance has been derived. This result in combination with a 2_III^6-3 fractional factorial design allowed to conclude column polarity to be only statistically relevant factor as compared to gas flow, split ratio, injection temperature, temperature program offset and column brand.

Development of retention time indices for comprehensive multidimensional gas chromatography and application to ignitable liquid residue mapping in wildfire investigations

In this study, we introduce a simple three-step workflow for a universally applicable RI system, to be used in GC×GC analysis of ignitable liquid residue (ILR) for arson investigations. The proposed RI system applies a combination of two well-established GC RI systems: non-isothermal Kovats (K) index in the first dimension and Lee (L) index in the second dimension. The proposed KLI RI system showed very good correlations when compared with predicted values and existing RI systems (r² = 0.97 in first dimension, r² = 0.99 in second dimension) and was valid for a wide range of analyte concentrations and operational settings (coefficient of variance (CV) < 1% in first dimension, < 10% in second dimension). Using the KLI RI, an ILR classification contour map was created to assist with the identification of ILR types within ASTM E1618. The contour map was successfully applied to neat fuels and a fire scene sample, highlighting the application to wildfire investigation. Standardizing the RI process and establishing acceptable error margins allows the exploration and comparison of comprehensive data generated from GC×GC analysis of ILRs regardless of location, time, or system, further enhancing comprehensive and tenable chemometric analyses of samples. Overall, the KLI workflow was inexpensive, quick to apply, and user-friendly with its simple 3-step design.

Qualitative analysis of flavors and fragrances added to tea by using GC-MS

A precise identification method was developed to identify the flavors and fragrances added to tea matrix artificially using gas chromatography with mass spectrometry and gas chromatography with quadrupole time-of-flight mass spectrometry. The proposed method was based on the corresponding "three-column retention indices, two exact mass numbers, one mass spectrum matching degree" database of 40 kinds of common flavors and fragrances. The intraday and the interday relative standard deviation of the retention indices were less than 0.048 and 0.093%, respectively. The accuracy of exact mass was between 0.15 and 6.22 ppm. And the validation of the created database was performed by analyzing the tea samples. Thus, the proposed method is suitable for the precise identification of the flavors and fragrances added to tea matrix artificially without standard substances as a reference.