In situ derivatisation and extraction of volatile fatty acids entrapped on anion-exchange resin from aqueous solutions and urine as a test matrix using pentafluorobenzyl bromide in supercritical carbon dioxide

Abstract

The simultaneous extraction and derivatisation of anion-exchange resin-trapped volatile fatty acids (C 2–C 5) as their pentafluorobenzyl esters has successfully been performed under CO 2 supercritical fluid extraction conditions. Volatile fatty acid standards of acetic, propionic and n-butyric acids (at 20 and 100 ppm) as their ester derivatives were recovered at 78.0–101.5% (C.V. 3.5–7.5%, n=6 and 7). Likewise, acrylic acid recoveries were 57.0–61.0% (C.V. 5.5–5.6%, n=6 and 7). This methodology was applied to the quantitation of acetic, propionic, n-butyric and n-valeric acids in spiked urine as a test matrix. Initial clean-up of phosphate and sulfate in the urine was required prior to anion-exchange application and this was achieved by barium salt precipitation. Recoveries ranged from 36 to 66.5% (C.V. 5.9–14.4%, n=9 and 6).