Ultrahigh Resolving Power Ion Mobility Spectrometry with a Simple Pulser Circuitry

The pulsing circuitry for high resolving power drift-tube ion-mobility spectrometry is based on three avalanche photodiodes. These are switched on by illumination through optical fibers, which provide electrical insulation of the driver circuitry from the high voltage. The setup was tested with a series of quaternary ammonium ions introduced with an electrospray ion source. Two instruments with drift tubes of 10 and 30 cm length were employed and a separation voltage of up to 23.7 kV. Resolving powers above 200 could be achieved for the longer tube, which are comparable to those obtained with a previously employed more elaborate electrically floating pulser. The new pulser allows the creation of common two-state injection pulses as well as tristate pulses known to reduce the discrimination of low mobility ions. A comparison between the two pulsing regimes showed that, as predicted by theory, for the longer tube, the discrimination of low-mobility ions in the two-state shutter mode was less significant than for the shorter tube.