Solution cathode glow discharge coupled to atmospheric pressure chemical ionization for elemental detection of S and P in organic compounds

Abstract

We report a post-plasma chemical ionization approach to evaluate solution cathode glow discharge (SCGD) for S and P elemental analysis. Here, the SCGD serves as a reactor to produce chemical vapors for S and P from organic compounds containing these elements, while a corona discharge operated in negative mode is used to ionize the products. The approach creates long-lived ions in atmospheric pressure, enabling direct investigation of chemical vapor products via mass spectrometric and ion mobility separations. The investigations indicate that SCGD converts S and P to H2SO4 and H3PO4, respectively. These species are then ionized as HSO4HNO3− and H3PO4NO3HNO3− via reactions with NO3HNO3− produced by corona discharge. The response factors for P among several small molecules varies within 10% of the average response from the compounds, suggesting a reasonable species-independent characteristic. The response factors for S show larger variations among compounds, indicating a higher dependence of chemical vapor generation efficiency on analytes' chemical structures. Detection limits of 15 and 29 ng/mL are achieved for P and S detection, respectively. These figures are limited by background equivalent concentrations and low ion flux in the utilized ion mobility-time of flight mass spectrometer, indicating potential for significant improvements. In particular, the specificity of clustering for S and P-containing ions produced in this approach suggest facile analysis of S and P using quadrupole-based mass spectrometers for improved analytical performance.