Positive corona discharge ion source with IMS/MS to detect impurities in high purity Nitrogen

¹ Department of Experimental Physics, Comenius University, Mlynska dolina F2, 84248 Bratislava, Slovak Republic
² Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031, P.R. China

^a e-mail: martin.sabo@gmail.com

Received: 27 October 2010
Accepted: 9 February 2011
Published online: 21 July 2011

Abstract

We have applied the Ion Mobility Spectrometry/Mass Spectrometry (IMS/MS) and the Atmospheric Pressure Chemical Ionisation/Mass Spectrometry (APCI/MS) techniques to study the formation of the ions in the positive corona discharge (CD) in highly purified nitrogen with impurities at 100 ppt level. The main products observed were H₃O⁺(H₂O)_n ions (reduced ion mobility of 2.15 cm² V^-1 s^-1). Additionally, we have observed ions with reduced mobilities 2.42 cm² V^-1 s^-1 and 2.30 cm² V^-1 s^-1. The intensity of these ions was increasing with the increasing discharge current. We associated these peaks with NH₄⁺ and NO⁺(H₂O)_n. The formation of these ions results from trace amounts of O₂ and NH₃ in nitrogen. The time evolution of the ions in corona discharge has been studied using the APCI/MS technique in the time windows ranging from 100 μs to 2 ms. The present work indicates the ability of the IMS technique equipped with CD ions source to detect impurities below 100 ppt level.