Direct gas chromatographic determination of methomyl (lannate®) with microcoulometric nitrogen detection

A microcoulometric method is described for the direct determination of nanogram amounts of methomyl (S-methyl-N-(methylcarbamoyl)-oxy]thioacetimidate). An all-glass gas chromatographic system coupled to a microcoulometer with a nitrogen-specific cell was used. The column was packed with a mixture of 6% OV210 and 4% OV101 on Gas Chrom Q, as was the glass transfer tube which connected the chromatographic column to the pyrolysis furnace. Some loss occurred but response was linear from 125 to 20 ng and sensitivity was such that 20 ng of methomyl could be readily measured.