Gas-Liquid Chromatographic Determination of 4-Chlorophenoxyacetic Acid Residues in Mung Bean Sprouts

Abstract

A gas-liquid chromatographic (GLC) method is described for determining 4-chlorophenoxyacetic acid (CPA) residues in mung bean sprouts. The residues were extracted from samples by using ethyl acetate followed by liquid-liquid partition into 5% NaHCO3 solution. After acidification and reextraction with ethyl acetate, CPA was reacted with pentafluorobenzyl bromide (PFB-Br) to form the PFB derivative. The reaction mixture was separated on a silica gel column to remove excess reagent, and the derivative was eluted with a solution of 75% toluene in hexane. GLC separations were performed on a 3% OV-1 column at 230 degrees C. As low as 10 pg CPA could be quantitated, which is equivalent to about 0.05 ppm at residue level, using an electron capture detector. Recoveries of CPA from fortified mung bean sprouts (0.05, 0.20, and 0.50 ppm) ranged from 71 to 107%. The PFB derivative was further identified by gas chromatography-mass spectrometry.