• benzoic acid
• butyric acid
• GC-MS
• hexanoic acid
• indole-3-acetic acid
• Liquid–liquid extraction
• perfluorooctanoic acid
• propionic acid
• salicylic acid
• triethyloxonium salt

In this work of thesis we propose the derivatization with triethyloxonium tetrafluoroborate for the quantitation of several organic acids of biological relevance (indole-3-acetic acid, benzoic acid, salicylic acid, propionic acid, butyric acid and perfluorooctanoic acid). The accurate determination of these molecules is mandatory a) to understand the metabolic processes crucial for plant growth and development (indole-3-acetic acid, benzoic acid, salicylic acid); b) to determine analytes indicators of bacterial activity and of interest in nutrition, bacteriological and environmental studies (salicylic acid, propionic acid, butyric acid)[2]; to measure drugs metabolites after their administration (e.g. salicylic acid from aspirin)[3] d) to quantify environmental pollutants associated with adverse health effects (perfluorooctanoic acid)[4].
The aforementioned carboxylic acids were simultaneously extracted in slightly alkaline solution and ethylated with triethyloxonium tetrafluoroborate from various matrices (Nicotiana tabacum and Actinidia deliciosa leaves, urine and saliva from healthy volunteers). Compared to the common derivatization approaches for GC analysis, the proposed method is simple and offers a fast sample preparation, involving only centrifugation, derivatization and extraction of the resulting ethyl-ester with methyl tert-butyl ether.
We optimized some effective parameters of the derivatization step, such as pH of reaction medium, the amount of derivatization reagent, derivatization and extraction time. The ethyl esters were determined by gas chromatography–mass spectrometry (GC–MS), using the respective deuterated acids as internal standards. The method was validated in terms of linearity, repeatability, recovery, limit of detection and limit of quantitation, evaluation of matrix effect.