Effect of the Humidity on Analysis of Aromatic Compounds with Planar Differential Ion Mobility Spectrometry

In this paper, we demonstrate that humidity is a crucial parameter for analysis of aromatic compounds of low polarity with planar differential ion mobility spectrometry. Utilization of polar modifiers which are usually applied for the improvement of separation ability of DMS based systems does not improve the separation of aromatic compounds. Moreover, the peak area of the model compounds decreases with the increase of the modifier (water vapors and 2-propanole) concentration. The influence of the polar modifiers on the DMS separation ability was proven on examples of the six aromatic compounds (BTEX, 1,2,4-trimethylbenzene (TMB), and naphthalene) and one aliphatic compound (hexane). The influence of the modifier concentration on the compensation voltage, peak area, and peak width was investigated and discussed. The strong influence of the proton affinity of analytes on the peak area in the measurements with modifiers was demonstrated. Some notable aspects of the formation of the reactant ion positive are demonstrated and discussed.