Current status and need for standards in ion mobility spectrometry

Abstract

Ion mobility spectrometry (IMS) is a well established technique for the detection of many compounds of interest based on the reduced mobility (K0) values of their ions. While having the advantage of small size, weight, and power, IMS has been subject to low specificity and is subject to interferences that can cause false alarms in detectors used for security applications. The rate of false positive alarms is directly related to the detection window width required to maintain a high rate of true positive detections. These window widths are in turn a result of the historically available accuracy of reference measurements and the range of responses by multiple detectors. The windows cannot be arbitrarily reduced without risking an increase in the rate of false negative responses. Ongoing work has focused on high accuracy calibration as a means of decreasing the false alarm rates by reducing the variability between detectors which would allow for narrower detection windows. Central to the calibration procedure is the selection of an appropriate calibrant (or reference standard) that can be easily characterized and known with a high degree of certainty across a range of instrumental conditions. This review evaluates a number of previously proposed and potential calibrants against seven recommended criteria of suitability. We examine the sources of false positive alarms in IMS-based detectors and propose a calibration procedure based on high accuracy reference measurements. Initial results of applying this procedure in a post-processing manner are promising towards reducing detector variability and detection window width.