Towards a hand-held, fast, and sensitive gas chromatograph-ion mobility spectrometer for detecting volatile compounds

Abstract

Ion mobility spectrometers can detect gaseous compounds at atmospheric pressure in the range of parts per trillion within a second. Due to their fast response times, high sensitivity, and limited instrumental effort, they are used in a variety of applications, especially as mobile or hand-held devices. However, most real-life samples are gas mixtures, which can pose a challenge for IMS with atmospheric pressure chemical ionization mainly due to competing gas-phase ionization processes. Therefore, we present a miniaturized drift tube IMS coupled to a compact gas chromatograph for pre-separation, built of seven bundled standard GC columns (Rtx-Volatiles, Restek GmbH) with 250 μm ID and 1.07 m in length. Such pre-separation significantly reduces chemical cross sensitivities caused by competing gas-phase ionization processes and adds orthogonality. Our miniaturized GC-IMS system is characterized with alcohols, halocarbons, and ketones as model substances, reaching detection limits down to 70 pptv with IMS averaging times of just 125 ms. It separates test mixtures of ketones and halocarbons within 180 s and 50 s, respectively. The IMS has a short drift length of 40.6 mm and reaches a high resolving power of RP = 68.

P9.5 - Compact, ultra-fast polarity switching ion mobility spectrometer with gas chromatographic pre-separation

“…The individual sample components interact to different extents with the stationary phase, so that the individual substances of the sample leave the GC separated by retention time and thus reach the IMS one after the other. [1,9] In this work, a small GC convection oven is built. Inside two parallel columns (MXT-5) with inner diameter of 500 µm and a length of 300 cm are placed.…”

“…In this way, different ion species can be separated based on their specific ion mobility in a neutral gas. [1,2] In real applications, gas mixtures often consist of a large number of different substances, which can lead to chemical interferences during the ionization process. Thus, identification of individual substances in a gas mixture with IMS can be difficult.…”

“…Such pre-separation significantly reduces chemical interferences and thus target compound discrimination during ionization and adds another dimension of separationthe retention time. [1] Ion mobility spectrometry is an established analytical technique. Especially the combination with pre-separation by GC can be found in different applications, for example in food industry [3] and breath analysis [4].…”

Ultra-Fast Polarity Switching, Non-Radioactive Drift Tube for the Miniaturization of Drift-Time Ion Mobility Spectrometer

“…DT-IMS, normally working under ambient pressure, is a sensitive technique for the detection of gas phase charged molecules based on their different mobility in the electric field [1]. It can either work as a standalone device [2][3][4] or in conjunction with other analytical instruments like Gas Chromatograph (GC) as its detector [5][6][7]. Its popularity largely attributed to the successful application in the detection of trace explosives, narcotics, Chemical Warfare Agents (CWA) and Toxic Industrial Compounds (TIC) [8][9][10][11].…”

Coupling Droplet Microfluidics with Ion Mobility Spectrometry for Monitoring Chemical Conversions at Nanoliter Scale

“…In recent years, IMS has experienced a renaissance, especially through the combination with electrospray mass spectrometers and the commercial availability of corresponding instruments. − While such IMS-MS systems are extremely powerful analytical tools, they have lost the advantages of stand-alone IMS systems such as their small size, instrumental simplicity, robustness, and comparatively low cost. − Typical drift tube IMS, for example, has a tube length of only 5–20 cm and can nowadays already be 3D-printed. − Although the main focus of IMS is still presented in the gas-phase analysis, − it has been demonstrated that IMS is an attractive detector for monitoring liquid-phase chemical and biochemical reactions. − Zühlke et al presented a qualitative and quantitative determination of all reaction components of an organic three-step synthesis . Very recently, IMS was also applied for monitoring photocatalyzed isomerization reactions performed on a continuous-flow microchip reactor …”