In EPA Method 531.1, the carbamate insecticides are separated by reversed-phase HPLC and detected with postcolumn reaction and fluorescence detection. In place of postcolumn reaction, we show electrospray MS for the detection. Not every RP column can resolve all the critical pairs. Instead of using a full-length C8 column to accomplish the resolution of peaks 8 and 9, we use a short 100 mm column and then use the mass spectrometer to selectively detect each peak.