Determination of Trace Amounts of Aliphatic Acids in Natural Waters Using Liquid-Liquid Extraction

A procedure is developed and conditions are optimized for the preparation of natural water samples using liquid-liquid extraction without the preliminary filtration of acidified water and subsequent derivatization for the determination of trace concentrations of aliphatic carboxylic acids C6-C21 by gas chromatography-mass spectrometry. It is shown that, at the stage of extraction with hexane, less than one half of free carboxylic acids of this homologous series passes into the extract, while a significant amount is adsorbed on the walls of the extraction vessel, and they must be washed off with a solution of sodium carbonate in an ethanol-water mixture (4 : 1). Liquid-liquid extraction with hexane in combination with the conversion of acids to pentafluorobenzyl esters significantly simplifies the analysis procedure of natural waters containing suspended particles, humic substances and ensures the attainment of a limit of detection of 0.05 mu g/L for the analytes.