Simultaneous gas chromatographic determination of food preservatives following solid-phase extraction

A simultaneous method for the solid-phase extraction of five preservatives is presented. Of the different sorbent materials assayed, styrene-divinylbenzene polymers provided the highest adsorption efficiency. Samples are inserted into the flow system at pH 1, which results in increased selectivity. Elution is made with 150 mu l of ethyl acetate and 2 mu l aliquots of the eluate are manually injected into a gas chromatograph equipped with flame ionization detection. Of the two chromatographic columns of different polarity, that containing the more polar stationary phase assayed provided the better results by virtue of the acid character of the analytes. The limits of detection achieved range from 0.1 to 0.2 mg/l, and the precision is quite high (R.S.D.<4%). The potential of the proposed method was assessed by applying it to the determination of sorbic and benzoic acid in feeds. Solid samples require pretreatment involving liquid-liquid extraction, evaporation of the extract and dissolution of the residue in 0.1 M HNO3. Recoveries ca. 95% for p-hydroxybenzoic acid esters can thus be obtained. (C) 1998 Elsevier Science B.V. All rights reserved.