DETERMINATION OF CHLORINATED PESTICIDES BY CAPILLARY SUPERCRITICAL FLUID-CHROMATOGRAPHY MASS-SPECTROMETRY WITH POSITIVE-ION AND NEGATIVE-ION DETECTION

An interface between a capillary supercritical fluid chromatograph and a double-focusing mass spectrometer was developed. Modification of th e standard electron ionization (EI)-chemical ionization (CI) combinati on ion source was necessary to obtain useful mass spectra with negativ e-ion detection. A detection limit in the lower nanogram range of the chlorinated pesticides (DDT and dieldrin) was found irrespective of th e mode of detection. Positive-ion methane CI resulted in a relatively abundant [M + H]+ ion, whereas positive-ion isobutane and ammonia CI a ppeared not to be amenable to the detection of chlorinated pesticides. The EI-charge exchange mass spectra of the investigated pesticides ge nerally did not match the library mass spectra. In the negative-ion mo de, CO2 was an efficient moderating gas giving relatively large amount s of M-., in addition to some fragment ions. More fragmentation was ob served when N2O replaced CO2 as the mobile phase. No major effects on the mass spectra, obtained by using pure mobile phase, were observed o n adding methane, isobutane or ammonia.