Development of a headspace solid-phase microextraction procedure for the determination of free volatile fatty acids in waste waters

An analytical procedure based on headspace solid-phase microextraction (SPME) coupled to GC–flame ionization detection/Negative Chemical Ionization Mass Spectrometry has been developed for the determination of free volatile fatty acids (C2–C7) in waste water samples. Five different coatings have been evaluated and polydimethylsiloxane–Carboxen was the only fiber that allows a successful extraction of the shortest chain fatty acids (acetic and propionic). Several parameters such as extraction time and temperature, desorption conditions, agitation speed and sample volume have been optimized using the polydimethylsiloxane–Carboxen fiber. The linear dynamic range was over two–four orders of magnitude, depending on the acid. Procedural detection limits were in the low to medium μg/l levels and the RSDs were between 5.6% and 13.3%. To evaluate the applicability of the developed SPME procedure on real samples, fermented urban wastewaters were analysed.