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.

This study focuses on optimising the pre-treatment, derivatisation processes, and gas chromatography conditions for the determination of lactose in liquid dairy products. Efficiency of sample preparation consists in the coagulation of protein components in methanol, centrifugation, and subsequent drying in a nitrogen stream. Derivatisation of the monitored carbohydrates is performed using a two-step silylation process. The samples were analysed using gas chromatography with flame-ionisation detection (GC-FID). Based on the calibration of lactose content in the range of 0.1—10 % w/v, quantitative determination of this disaccharide was performed in 18 milk samples. The paper presents the results of quantitative analysis as well as dosing and derivatisation repeatability. This method compensates for time-consuming sample preparation by reducing the separation time of mono- and disaccharides to 16 minutes.