HEADSPACE GAS-LIQUID-CHROMATOGRAPHIC DETERMINATION OF DITHIOCARBAMATERESIDUES IN FRUITS AND VEGETABLES WITH CONFIRMATION BY CONVERSION TO ETHYLENETHIOUREA

Ethylene-bis-dithiocarbamate (EBDC) residues were determined as carbon disulfide (CS2) by an improved headspace gas-liquid chromatographic ( GLC) procedure. Among 837 samples of 30 agricultural commodities teste d, 43% contained residues above the detection limit for the method: 10 0% of broccoli samples; 80% of cabbage, kiwifruit, and grape samples; and 71% of cucumber samples. Most of the residues in kiwifruit were on or near the skin. Elimination of false-positive detections by the imp roved method was confirmed with kiwifruit in 2 independent procedures. Whole fruits were washed with 5% EDTA to remove surface residues of E BDC. Analysis of washes for CS2 by the headspace procedure after treat ment with acidic stannous chloride and for ethylene thiourea by LC aft er prolonged treatment at 60 degrees C qualitatively identified the ED TA-soluble residues as EBDC. Although the improved method does not pro duce false-positive results, peak area responses of CS2 and the intern al standard, thiophene, are influenced by chemical composition of the matrix. With matrixes high in sugar or lipids, the apparent CS2 conten t may be overestimated by 4-fold. Accurate determination of EBDC resid ues in these sample types requires appropriate adjustments to matrixes .