A corona discharge atmospheric pressure chemical ionization source with selective NO+ formation and its application for monoaromatic VOC detection

Abstract

We have developed a new type of corona discharge (CD) for atmospheric pressure chemical ionization (APCI) for application in ion mobility spectrometry (IMS) as well as in mass spectrometry (MS). While the other CD-APCI sources are able to generate H₃O⁺·(H₂O)_n as the major reactant ions in N₂ or in zero air, the present CD-APCI source has the ability to generate up to 84% NO⁺·(H₂O)_n reactant ions in zero air. The change of the working gas from zero air to N₂ allows us to change the major reactant ions from NO⁺·(H₂O)_n to H₃O⁺·(H₂O)_n. In this paper we present the description of the new CD-APCI and discuss the processes associated with the NO⁺ formation. The selective formation of NO⁺·(H₂O)_n reactant ions offers chemical ionization based on these ions which can be of great advantage for some classes of chemicals. We demonstrate here a significant increase in the sensitivity of the IMS-MS instrument for monoaromatic volatile organic compound (VOC) detection upon NO⁺·(H₂O)_n chemical ionization.