A GC/MSD method for the analysis of metolachlor in cabbage,broccoli, and tomato

Abstract

Metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐meth‐oxy‐1‐methylethyl)acetamide) is being considered for control of eastern black nightshade (Solarium ptycanthum Dun.) in cabbage (Brassica oleracea L. var. capitata), broccoli (B. oleracea L. var. Botrytis) and tomato (Lycopersicon esculentum Mill.). We have developed a rapid, sensitive method to determine metolachlor residues in these commodities to ensure its absence in the edible tissue. The crop material was extracted with methanol, the extract partitioned with hexane, then passed through a silica cartridge and analysed for metolachlor by GC/MSD in selected ion mode at m/z 161. Recovery of metolachlor from fortified plant material was greater than 84%. The method detection limit was calculated to be 0.6 ppb for tomato, 1.1 ppb for cabbage, and 4.2 ppb for broccoli. Metolachlor residues were below the detection limit in all commodities harvested from treatments which received 2 or 3 kg metolachlor/ha.