Multiresidue Method for Determining N-Methylcarbamate Insecticides in Crops, Using High Performance Liquid Chromatography

Abstract A method is described for determining 7 carbamate insecticide residues (aldicarb, bufencarb, carbaryl, carbofuran, methiocarb, methomyl, and oxamyl) and 4 related carbamate metabolites (aldicarb sulfone, aldicarb sulfoxide, 3-hydroxy carbofuran, and methiocarb sulfoxide) on fruits, vegetables, and grains. Residues are extracted from the crops using methanol, and plant coextractives are removed using solvent partitioning and a charcoal-silanized Celite column. The carbamate residues are then separated on a reverse phase high performance liquid chromatographic (HPLC) column using an acetonitrile-water gradient mobile phase. The eluted residues are detected using an in-line post-column fluorometric detection technique. Recovery data were obtained by fortifying 9 crops (apples, carrots, green beans, green peppers, lettuce, oranges, soybeans, strawberries, and tomatoes) with the 7 carbamates and 4 carbamate metabolites. Except for aldicarb sulfoxide, pesticide recovery averaged 99% at both the 0.05 and 1.0 ppm fortification levels, with standard deviations of 5.0% (n = 86) and 5.6% (n = 87), respectively. The average recovery for aldicarb sulfoxide, a very polar carbamate metabolite, was 55 and 57% at the 0.05 and 1.0 ppm levels, respectively. An intralaboratory study of the method was conducted. Recovery data were obtained by fortifying grapes and potatoes with carbaryl, carbofuran, 3-hydroxy carbofuran, methiocarb, and methomyl at levels ranging from 0.05 to 15 ppm. Determinations were made in duplicate and the average recovery was 95% (range 87–101%).