Headspace gas-liquid chromatographic determination of dithiocarbamate residues in fruits and vegetables with confirmation by conversion to ethylenethiourea
Ahmad, N.; Guo, L.; Mandarakas, P.; Farah, V.; Appleby, S.; Gibson, T.
Journal - Association of Official Analytical Chemists 79(6): 1417-1422
1996
ISSN/ISBN: 0004-5756 PMID: 8946720 Document Number: 462589
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 tested, 43% contained residues above the detection limit for the method: 100% 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 improved method was confirmed with kiwifruit in 2 independent procedures. Whole fruits were washed with 5% EDTA to remove surface residues of EBDC. Analysis of washes for CS-2 by the headspace procedure after treatment with acidic stannous chloride and for ethylene thiourea by LC after prolonged treatment at 60 degree C qualitatively identified the EDTA-soluble residues as EBDC. Although the improved method does not produce false-positive results, peak area responses of CS-2 and the internal standard, thiophene, are influenced by chemical composition of the matrix. With matrixes high in sugar or lipids, the apparent CS-2 content may be overestimated by 4-fold. Accurate determination of EBDC residues in these sample types requires appropriate adjustments to matrixes.