Performance of a Low Cost Atmospheric Pressure Chemical Ionization-interfaced Thermospray Ion Source

Abstract

The combination of a custom-made atmospheric pressure chemical ionization interface with a thermospray (TSP) ion source is described. The sensitivity is comparable with normal specifications of commercially available interfaces. The TSP ion source is used as an intermediate pressure region to force ions by means of a repeller into the mass spectrometer. The TSP ion source pressure has been optimized with respect to transmission and ion energy distribution and has been used, in conjunction with optimization of the repeller voltage, to increase the sensitivity of the interface. Using optimal conditions, 50 pg of reserpine can be detected with a signal-to-noise ratio of 20 in selected-ion monitoring. The performance of the interface coupled with liquid chromatography in negative ionization mode for the analysis of some steroids is also described. In this case absolute detection limits of 40 pg, corresponding to a sample concentration detection limit of 2 ng/mL, have been obtained.