PERFORMANCE OF A LOW-COST ATMOSPHERIC-PRESSURE CHEMICAL IONIZATION-INTERFACED THERMOSPRAY ION-SOURCE

The combination of a custom-made atmospheric pressure chemical ionizat ion interface with a thermospray (TSP) ion source is described, The se nsitivity is comparable with normal specifications of commercially ava ilable interfaces. The TSP ion source is used as an intermediate press ure region to force ions by means of a repeller into the mass spectrom eter. The TSP ion source pressure has been optimized with respect to t ransmission and ion energy distribution and has been used, in conjunct ion with optimization of the repeller voltage, to increase the sensiti vity of the interface. Using optimal conditions, 50 pg of reserpine ca n be detected with a signal-to-noise ratio of 20 in selected-ion monit oring. The performance of the interface coupled with liquid chromatogr aphy in negative ionization mode for the analysis of some steroids is also described, In this case absolute detection limits of 40 pg, corre sponding to a sample concentration detection limit of 2 ng/mL, have be en obtained.