Positive corona discharge ion source with IMS/MS to detect impurities in high purity Nitrogen M. Sabo, M. Klas, H. Wang, C. Huang, Y. Chu and Š. Matejčík Eur. Phys. J. Appl. Phys., 55 1 (2011) 13808 Published online: 21 July 2011 DOI: 10.1051/epjap/2011100437