SIMULTANEOUS PULSED FLAME PHOTOMETRIC AND MASS-SPECTROMETRIC DETECTION FOR ENHANCED PESTICIDE ANALYSIS CAPABILITIES

Analysis of pesticides by simultaneous pulsed flame photometric detect ion (PFPD) and mass spectrometric (MS) detection was performed with co lumn-effluent splitting between these two detectors. The resulting PFP D chromatograms were always much simpler due to the PFPD selectivity a nd were further characterized by better sensitivity than that of MS. A ccordingly, the PFPD chromatogram served as a marker for the exact elu tion time of the suspected pesticide. At this exact elution time, the resulting mass spectra were examined for unique high-mass peaks and a precise background subtraction was performed for improved library iden tification. If no definite identification was achieved, reconstructed mass chromatograms were performed, inspected for suspected major ions and confirmed with the PFPD chromatogram. A sequential search was then performed with the NIST library. The presence of P or S atoms was int roduced into the search algorithm and two of the major suspected fragm ent mass peaks were included with an estimate of their minimum relativ e abundance. Under these conditions, the library search provided the c orrect pesticide identification? at a considerably lower concentration than achievable with standard GC-MS analysis. If only information on a single ion was available, such as with very pronounced matrix interf erences, or with single-ion monitoring MS analysis, the NIST library s equential search was operated with this single-ion information and PFP D provided information on both P and S (the majority of organophosphor us pesticides contain both P and S). The incorporation of one major io n and two heteroatoms' (P and S) information enabled an effective libr ary identification, at an even further reduced pesticide concentration . The simultaneous PFPD-MS analysis approach is demonstrated and discu ssed with several examples of authentic pesticides in vegetable and sp ices. The merits of this method are analyzed and discussed with an emp hasis on the unique suitability of PFPD for combination with MS. (C) 1 998 Elsevier Science B.V. All rights reserved.