STEP-WISE optimization of a flexible Micro tube plasma (FμTP) as an ionization source for ION Mobilityspectrometry

Abstract The ionization source is the central system of analytical devices such as mass spectrometers or ion mobility spectrometers. In this study, a recently developed Flexible Micro Tube Plasma (FμTP) is applied as an ionization source for a custom-made drift tube ion mobility spectrometer (IMS) for the first time. The FμTP is based on a highly miniaturized, robust and a small-footprint dielectric barrier discharge design with an outstanding ionization efficiency. In this study, the experimental setup of the FμTP was further improved upon to achieve optimal coupling conditions in terms of the ion mobility spectrometry sensitivity and the plasma gas consumption. One major focus of this study was the adjustment of the electrical operation parameters, in particular, the high voltage amplitude, frequency and duty cycle, in order to minimize the electric field disturbances and yield higher signals. Additionally, the consumption of helium plasma gas was reduced by refining the FμTP. It was found that the ionization efficiency could be significantly enhanced by increasing the plasma high voltage and through application of a duty cycle up to 90:10. Plasma gas flows could be reduced down to 10-3 mL min-1 by increasing the plasma high voltage amplitude. Furthermore, a smaller wire electrode design enables the operation of the FμTP with nitrogen and clean air. Moreover, detection limits of a homologous series of ketones in the range of 330 pptv (N2-FμTP, 2-decanone) down to 20 pptv (He-FμTP, 2-octanone) could be reached in the optimized setup. To sum up, this feasibility study demonstrates the potential of the optimized FμTP as a powerful ionization source for ion mobility spectrometry especially with regard to ionization efficiency.