A capillary isotachophoresis (CITP) method performed in a column-coupling apparatus has been developed for the simultaneous determination of glutathione (GSH) and glutathione disulfide (GSSG) concentrations in blood samples. The determination of GSSG and GSH concentrations in biological samples is important because of their roles in oxidative stress. Different concentrations of a leading ion in the coupled columns (concentration cascade) and a large volume (37 µ ) of the injected sample facilitated a GSSG concentration of between 2 and 25 µmol/l. A reaction between iodoacetate and GSH under alkaline conditions was used to prepare the sample in order to avoid oxidation of GSH to GSSG. This step eliminated the main source of systematic errors with regard to the determination of the GSSG concentration. A linear relationship (R2=0.9969) between the zone length of S-(carboxymethyl)glutathione (the product of the reaction between GSH and iodoacetate) and the concentration of GSH (40-120 µmol/l) was obtained. The method was applied to the analysis of bovine blood samples that had been diluted by a factor of ten with satisfactory results

Essential oils are natural products frequently subject to economically motivated adulteration with cheaper substances like vegetable oils, mineral oils, or organic solvents. This study developed and validated a rapid high-temperature gas chromatography with flame ionization detection (HTGC-FID) method for the simultaneous determination of high-boiling adulterants: triacylglycerides (vegetable oils) and medicinal white oil (mineral oil) in essential oils. The method utilizes on-column injection onto a DB-5 capillary column (30 m × 0.53 mm, 0.88 μm) with a temperature program from 60 to 380 °C and hydrogen carrier gas. Validation parameters demonstrated excellent linearity (R² = 0.9957–0.9978), high repeatability (content RSD < 3%), and sufficient sensitivity (LOQ of 0.03% for triacylglycerides, and 0.63% for medicinal white oil). The method was successfully applied to 20 commercial essential oils. While medicinal white oil was undetected, several samples contained triacylglycerides (up to 3.79%) and other adulterants (up to 52%). Significantly reduced response factors confirmed extensive adulteration in some products. The proposed HTGC-FID method represents a simple, cost-effective, and efficient tool for routine quality control, enabling direct quantification of high-boiling adulterants without tedious sample preparation.