Simultaneous pulsed flame photometric and mass spectrometric detection for enhanced pesticide analysis capabilities

Abstract

Analysis of pesticides by simultaneous pulsed flame photometric detection (PFPD) and mass spectrometric (MS) detection was performed with column-effluent splitting between these two detectors. The resulting PFPD chromatograms were always much simpler due to the PFPD selectivity and were further characterized by better sensitivity than that of MS. Accordingly, the PFPD chromatogram served as a marker for the exact elution 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 identification. 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 introduced into the search algorithm and two of the major suspected fragment mass peaks were included with an estimate of their minimum relative abundance. Under these conditions, the library search provided the correct 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 interferences, or with single-ion monitoring MS analysis, the NIST library sequential search was operated with this single-ion information and PFPD provided information on both P and S (the majority of organophosphorus pesticides contain both P and S). The incorporation of one major ion and two heteroatoms' (P and S) information enabled an effective library identification, at an even further reduced pesticide concentration. The simultaneous PFPD–MS analysis approach is demonstrated and discussed with several examples of authentic pesticides in vegetable and spices. The merits of this method are analyzed and discussed with an emphasis on the unique suitability of PFPD for combination with MS.