A novel electron source for negative ion mobility spectrometry

Abstract

The possibility of using negative corona discharge in pure nitrogen as the ionization source for negative ion mobility spectrometry (IMS) has been investigated. The discharge in pure nitrogen produces a huge number of electrons, almost 10 6 times as much as that produced by the conventional 63 Ni ionization source. However, this high intensity electron source cannot be simply used in IMS since introducing any electronegative substance in the corona region immediately results in quenching of the discharge. In this connection, a special IMS cell has been designed and optimized to employ this intense electron source without being disturbed by sample. With this design, the electron current received at the detector plate could be as high as 200 nA. The ionization efficiency and the collection efficiency of the electrons and negative ions, as a function of electric field at different regions, have been evaluated. As practical examples, the IMS spectra of CHCl 3, CHBr 3, CH 3I and nitrobenzene, as well as the explosive materials pentaerythritol tetranitrate (PETN) and trinitrotoluene (TNT) at elevated temperatures have been obtained. Finally, the capability of the method in quantitative analysis of CHCl 3 has been evaluated and a detection limit of 10 ng/m 3 and a linear range of five orders of magnitude were obtained.