Comparative measurements of toxic industrial compounds with a differential mobility spectrometer and a time of flight ion mobility spectrometer

Small concentrations of toxic compounds in atmospheric air have often to be measured selectively by portable equipment. Ion mobility spectrometers are instruments used to monitor explosives, drugs and chemical warfare agents. First responders also need to detect hazardous gases released in accidents while transporting them or in their production in chemical plants. Not all toxic gases can be measured with the time of flight ion mobility spectrometer at concentrations required by safety standards applied in workplace areas. The time of flight ion mobility spectrometer is based on an inlet membrane, an ionization region, a shutter grid and the drift region with a detector in the drift tube. The separation of ions is due to the different mobility of the ions when they are exposed to a weak electric field (E = 200…300 V/cm). High field asymmetric waveform spectrometry or differential mobility spectrometry is a relative new ion mobility spectrometer technology. The separation is due to the different mobilities of the ions in the high (E = 15000...30000 V/cm) and the weak electric fields. About 30 different toxic industrial chemical compounds were analyzed with both systems under comparable conditions. For selected examples the detection limits, the selectivity and the identification capabilities of the two systems for some of the main compounds will be discussed.