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

André Ahrens,Stefan Zimmermann

doi:10.1007/s00216-020-03059-9

André Ahrens, Stefan Zimmermann

Open Access

https://doi.org/10.1007/s00216-020-03059-9

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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.Graphical abstract

Highlights

Drift tube ion mobility spectrometers (IMS) often consist of three axially arranged regions: the reaction, drift, and detector regions
Due to the temporal pre-separation by the gas chromatograph (GC), the measurement results from the GC-IMS are two-dimensional
Coupling a compact GC for pre-separation to our miniaturized IMS adds orthogonality and significantly reduces chemical cross sensitivities when measuring gas mixtures

Summary

Introduction

Drift tube ion mobility spectrometers (IMS) often consist of three axially arranged regions: the reaction, drift, and detector regions. As required for hand-held devices with sufficient separation power as well as carrier gas flow rates suitable for IMS, several columns in parallel with small inner diameter are beneficial [23]. We present a compact GC-IMS, consisting of a miniaturized high-performance drift tube IMS and a small GC, built from seven bundled commercially available standard GC columns (Rtx-Volatiles, Restek GmbH) with 250 μm ID and 1.07 m in length. Since condensation of eluents in the transfer line between the GC and the IMS must be avoided, the six-port valve seat, sample loop, GC, and IMS drift tube are all placed together in a small, thermally insulated housing with outer dimensions of only 170 mm × 110 mm × 55 mm.

Results and discussion

Conclusion

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