Developing powerful hand-held drift tube ion mobility spectrometers (IMS) requires small, lightweight drift tubes with high analytical performance. In this work, we present an easy-to-manufacture, miniaturized drift tube ion mobility spectrometer, which is manufactured from polyether ether ketone, stainless steel foils and printed circuit boards. It is possible to operate the drift tube IMS with a radioactive 3 H ionization source or a non-radioactive X-ray ionization source with 3 kVacceleration voltage. The drift tube design provides high resolving power of R p = 63 at a drift length of just 40 mm, 15 mm × 15 mm in cross-section (outer dimensions) and a drift voltage of 2.5 kV. The limits of detection for less than one second of averaging are 40 ppt v for dimethylmethylphosphonate and 30 ppt v for methyl salicylate. For demonstration, the miniaturized drift tube IMS is integrated into a stand-alone battery-powered mobile device, including a closed gas-loop, high performance driver electronics and wireless data transmission. In a proof-of-concept study, this device was tested in an international field evaluation exercise to detect the release of a volatile, hazardous substance inside a large entry hall.
Abstract. Split-ring resonators are electrical circuits, which enable highly sensitive readout of split capacity changes via a measurement of the shift in the resonance frequency. Thus, functionalization of the split allows the development of biosensors, where selective molecular binding causes a change in permittivity and therefore a change in split capacity. In this work, we present a novel approach using transmission line theory to describe the dependency between permittivity of the sample and resonance frequency. This theory allows the identification of all relevant parameters of a split-ring resonator and thus a target-oriented optimization process. Hereby all setup optimizations are verified with measurements. Subsequently, the split of a resonator is functionalized with aptamers and the sensor response is investigated. This preliminary experiment shows that introducing the target protein results in a shift in the resonance frequency caused by a permittivity change due to aptamer-mediated protein binding, which allows selective detection of the target protein.
Due to their high sensitivity and compact design, ion mobility spectrometers are widely used to detect toxic industrial chemicals (TICs) in air. However, when analyzing complex gas mixtures, classical ion mobility spectrometry (IMS) suffers from false-positive rates due to limited resolving power or false-negative rates caused by competitive ion−molecule reactions and the resulting suppression of certain analyte ions. To overcome these limitations, high-kinetic energy IMS (HiKE-IMS) was introduced some years ago. In contrast to classical IMS, HiKE-IMS is operated at decreased pressures of 20•••60 mbar and high reduced electric field strengths E/N of up to 120 Td. Under these conditions, the influence of competitive ion−molecule reactions on the prevailing ion population should be less pronounced, thus reducing false negatives. Additionally, effects such as fragmentation and field-dependent ion mobility may help to reduce false positives. In this work, the capabilities and limitations of HiKE-IMS in the field of on-site detection of the volatile TICs NH 3 , HCN, H 2 S, HCl, NO 2 , Cl 2 , and SO 2 are evaluated for the first time. Based on the limits of detection and the extent of spectral and chemical cross-sensitivities in gas mixtures, the results obtained for HiKE-IMS are compared with those obtained for classical IMS. It is shown that HiKE-IMS is less sensitive in comparison to classical IMS. However, when used for TIC detection, the reduced sensitivity of HiKE-IMS is not a major drawback. With values around 1 ppm v , the achievable limits of detection for almost all TICs are below the AEGL-2 (4h) levels. Furthermore, in comparison to classical IMS, it is still striking that HiKE-IMS shows significantly less spectral and chemical cross-sensitivities and thus exhibits considerably lower false-positive and false-negative rates. Overall, it thus turns out that HiKE-IMS is a promising alternative to classical IMS in the field of on-site detection of TICs.
A growing demand for low-cost gas sensors capable of detecting the smallest amounts of highly toxic substances in air, including chemical warfare agents (CWAs) and toxic industrial chemicals (TICs), has emerged in recent years. Ion mobility spectrometers (IMS) are particularly suitable for this application due to their high sensitivity and fast response times. In view of the preferred mobile use of such devices, miniaturized ion drift tubes are required as the core of IMS-based lightweight, low-cost, hand-held gas detectors. Thus, we evaluate the suitability of a miniaturized ion mobility spectrometer featuring an ion drift tube length of just 40 mm and a high resolving power of R p = 60 for the detection of various CWAs, such as nerve agents sarin (GB), tabun (GA), soman (GD), and cyclosarin (GF), as well as the blister agent sulfur mustard (HD), the blood agent hydrogen cyanide (AC) and the choking agent chlorine (CL). We report on the limits of detection reaching minimum concentration levels of, for instance, 29 pptv for sarin (GB) within an averaging time of only 1 s. Furthermore, we investigate the effects of precursors, simulants, and other common interfering substances on false positive alarms.
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