Liquid chromatographic determination of N-methylcarbamate insecticides and metabolites in crops. II. Analytical characteristics and residue findings.

Four laboratories obtained 177 carbamate recovery values using a liquid chromatographic method. The average recovery of 11 carbamates (aldicarb, aldicarb sulfone, bufencarb, carbaryl, carbofuran, 3-hydroxy carbofuran, 3-keto carbofuran, methiocarb, methiocarb sulfoxide, methomyl, and oxamyl) from 14 crops was 99% with a coefficient of variation of 8% (0.03-1.8 ppm fortification levels). No statistical difference in recovery was found between oxime and phenyl carbamates, or between parent and metabolite carbamates. Average recovery of aldicarb sulfoxide was 59% due to loss in the liquid-liquid partitioning because of the polarity of this compound. A fifth laboratory contributed 34 carbamate recoveries (average 99%) on table-ready food products for 4 carbamates. Bendiocarb, dioxacarb, isoprocarb, and propoxur are also quantitatively recovered through the method. Previously reported carbamate and noncarbamate recovery data are also discussed. In the Food and Drug Administration's (FDA) analysis of 319 samples (mainly crops), 86 (27%) were found to contain residues of carbamate insecticides and/or toxic carbamate metabolites. Carbaryl and methomyl were the most common carbamate residues found on the food products excluding the aldicarb sulfone and sulfoxide residues found on potatoes. In one FDA Total Diet Program "market basket", 11 of 69 table-ready food commodities contained from 0.005 to 0.094 ppm carbamate residues. Carbaryl was the most prevalent residue. Several laboratories reported adverse effects on the determinative system when inadequately purified reagents were used.