Inverse ion mobility spectrometry.

A novel method is proposed for enhancing the separation power of ion mobility spectrometry (IMS) and other similar pulsed techniques, such as time-of-flight mass spectrometry. In this technique, rather than generating an ion packet, a dip is created in the ion beam. This is achieved by an inverse pulse applied to the shutter grid. The dip moves with the same velocity as the ion packet, and the detector reads an inverse peak at the same drift time as that of the normal operation. Using this technique, we achieved 30-60% higher resolution compared to the normal method. In addition, two close peaks that were not resolved via normal IMS were well resolved to the baseline using this technique. The main reason for the increased resolution is likely the absence of space charge in the dip.