USE OF CHEMICAL-IONIZATION IN MULTIANALYSIS GAS AND LIQUID-CHROMATOGRAPHY COMBINED WITH A SINGLE MASS-SPECTROMETER FOR THE ULTRA-TRACE LEVEL DETERMINATION OF MICROCONTAMINANTS IN AQUEOUS SAMPLES

An automated system that comprises a single mass spectrometer (MS) in combination with gas (GC) and liquid chromatography [LC; particle beam (PB) interface] has been used for the trace-level detection and ident ification of contaminants in water samples, The analytes mere enriched by on-line solid-phase extraction (SPE). In the present study, the po tential of negative chemical ionization (NCI) detection in this so-cal led multianalysis system was explored, Attention was devoted to the en hancement of selectivity and sensitivity as well as to the additional spectral information obtained for the identification of unknown compou nds. Nine chlorinated pesticides representing three major groups, i.e. , triazines, anilides and organophosphorus pesticides, mere used as te st compounds, Among the three reagent gases used for NCI, isobutane, m ethane and ammonia, methane gave the best results, For sis of the nine pesticides, a 3- to 30-fold increase in sensitivity was observed in t he NCI mode as compared with the electron impact (EI) mode, As expecte d, the NCI mass spectra showed little fragmentation, Electron capture appears to be the dominant ionization mechanism. In order to study the potential of the total on-line SPE-LC/GC-MS set-up, the pesticides we re spiked to tap and surface mater samples, The detection limits obtai ned in the NCI (full-scan) mode ranged from 0.1-3 ng l(-1) for GC-MS a nd 50 to 200 ng l(-1) for LC-PB-MS for 100-ml tap mater samples, The p otential of NCI-MS was demonstrated by the identification of several u nknown microcontaminants in a river mater sample.