Analysis of chlorophenoxy acids and other acidic contaminants in food crops.

Several chlorophenoxy acids and chlorinated phenols were determined by means of gas chromatography in contaminated samples of cereals. Extraction of plant matrix with acetone/water mixture followed by alkaline hydrolysis was proved to be suitable for isolation of both free and conjugated residues. The use of pentafluorobenzyl bromide for volatilization of analytes, despite of enhanced ECD response, cannot be recommended for routine analysis. Methylation with either methanol/sulphuric acid or methanol/BF3 reagent can substitute diazomethane-based esterification procedure. Mass fragmentography provided the highest selectivity of detection, moreover good sensitivity--5 ppb--was achieved in this way. Even methyl derivatives of monochlorinated analytes could be, contrary to GC/ECD analysis, quantitated at this level.