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 the standard electron ionization (EI)-chemical ionization (CI) combination ion source was necessary to obtain useful mass spectra with negative-ion detection. A detection limit in the lower nanogram range of the chlorinated pesticides (DDT and dieldrin) was found irrespective of the mode of detection. Positive-ion methane CI resulted in a relatively abundant [M + H]+ ion, whereas positive-ion isobutane and ammonia CI appeared not to be amenable to the detection of chlorinated pesticides. The EI-charge exchange mass spectra of the investigated pesticides generally did not match the library mass spectra. In the negative-ion mode, CO2 was an efficient moderating gas giving relatively large amounts of M-., in addition to some fragment ions. More fragmentation was observed when N2O replaced CO2 as the mobile phase. No major effects on the mass spectra, obtained by using pure mobile phase, were observed on adding methane, isobutane or ammonia.