Gas chromatography-flame ionization detector for sweat based COVID-19 screening.

Simple approach for rapid screening of corona virus disease 2019 (COVID-19) has been developed. This applied gas chromatography-flame ionization detector (GC-FID) analyzing the potential compound marker in sweat samples obtained from COVID-19 positive and negative volunteers in Bangkok, Thailand. The samples were collected by using cotton rods for 15 min, heated at 90 °C for 5 min, and the volatile compounds in the headspace (HS) were injected (5.00 mL) at 150 °C and separated within 13.7 min. The marker peak was tentatively identified as p-cymene by the authentic standard injection and comparison with the GC-mass spectrometry (GC-MS) and comprehensive two-dimensional GC (GC × GC)-MS analysis. Possible mechanisms for the presence of p-cymene were proposed. The marker peak area thresholds were then varied and optimized via construction of the receiver operating characteristic (ROC) curve. With the optimum threshold, the established method offered the accuracy, sensitivity and specificity of 96 %. This method was insignificantly affected (p-value >0.05) by genders, body mass indices, ages, and use of deodorants as well as the p-cymene containing food. However, the performance could be affected by the population with personal hygiene or experiencing the microbiomes producing p-cymene.

Development and Application of a Novel Multiloop Splitter-Based Non-cryogenic Artificial Trapping Modulation System in Comprehensive Two-Dimensional Gas Chromatography.

A multiloop splitter-based non-cryogenic artificial trapping (M-SNAT) modulation technique was established, which applied the first (1D) nonpolar and the second (2D) polar columns, deactivated fused silica (DFS) columns, a microfluidic Deans switch (DS), and splitters located between the 1D column outlet and the DS. The splitters were connected into multiple loops with a progressively doubled perimeter of the next loop. This enabled a duplex splitting mechanism within each loop consisting of splitting of analyte pulses, the pulse delay, and their combination which led to equally split peaks of the same analytes with the number of split peaks (nsplit) equal to 2m (m = number of loops). This system resulted in local profiles of artificially split-and-trapped analytes prior to their selective transfers onto the 2D column by means of periodic multiple heart-cuts (H/C). The developed SNAT approach can be successful, providing that the ratio of modulation period to sampling time (PM/tsamp) is equal to nsplit. The approach with nsplit = 16 was further developed into a single device platform and applied for the modulation of a wide range of compounds in waste tire pyrolysis samples with the RSD of ≤0.01 and <10% for the one-dimensional modulated peak times and peak areas, respectively (n = 50). The method enabled an artificial modulation mechanism without cryogen consumption and enhanced the 2D peak capacity (2nc) and 2D separation by use of a longer 2D column.

Simultaneous determination of benzoic acid, sorbic acid, and propionic acid in fermented food by headspace solid-phase microextraction followed by GC-FID.

A simple and environmentally friendly method was developed for simultaneous determination of benzoic acid, sorbic acid, and propionic acid in fermented food samples. The analytes were extracted and pre-concentrated by headspace solid-phase microextraction (HS-SPME) and analysed by GC-FID. Central composite design (CCD) was conducted for the optimization of HS-SPME conditions. Under optimal conditions, a good linear range was obtained in the range of 5-150 mg L-1. The limit of detection (LOD) values were 1.1-1.7 mg L-1. The developed method was successfully applied to determine the concentration of three organic acid preservatives in various fermented food samples, including thai shrimp paste, pickled vegetables, soy sauce and fish sauce, with high accuracy (recoveries were between 83% and 109%) and good precision (%RSD was less than 6.0% and 4.5% for intra-day and inter-day, respectively).

A colorimetric paper-based analytical device coupled with hollow fiber membrane liquid phase microextraction (HF-LPME) for highly sensitive detection of hexavalent chromium in water samples.

A simple and highly sensitive procedure based on the combination of hollow fiber membrane liquid phase microextraction and a microfluidic paper-based analytical device (µPAD) was developed for pre-concentration and determination of hexavalent chromium in water samples. The hexavalent chromium was pre-concentrated using the HF-LPME technique via ion exchange or a coupled transport process through a supported ionic liquid (Aliquat 336) prior to colorimetric detection with diphenylcarbazide on the µPAD. The violet colour could be seen by the naked eye. Images from the µPADs were scanned using a commercial desktop scanner at 600 dpi resolution. ImageJ software was used for quantitative analysis by measuring the intensity values at green colour channel since it gave the best sensitivity among the RGB colour. Under optimal conditions, the calibration curve was linear in the range 10-90 µg L-1, with a limit of detection of 3 µg L-1. The developed method was successfully applied to determine the level of hexavalent chromium spiked into natural water samples at the parts-per-billion (ppb) level, and the results were in good agreement with those obtained using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The developed method was able to improve the detection limit of the conventional µPAD, and was expected to be used for the effective analysis of hexavalent chromium in natural water.

Synthesis and isolation of non-chromophore cage-rearranged silsesquioxanes from base-catalyzed reactions.

The nucleophilicity of both ortho- and meta-nitrophenolate anions is strong enough to give substituted products, but their basicity also facilitates cage-rearrangement reactions in polyhedral oligomeric silsesquioxanes (POSS). Anions having a stronger basicity, but weaker nucleophilicity, such as CO32-, gave products only from cage-rearrangement, with the cage expansion products being isolable in multi-gram quantities using conventional column chromatography.