| 08 Oct 2026
Bridging temporal resolution and molecular specificity with a compact GC-PTR for the measurement of volatile organic compounds
Abstract. Volatile organic compounds (VOCs) play important roles in atmospheric chemistry and air quality, but measurements often require a tradeoff between temporal resolution, molecular specificity, and instrument size and complexity. Online chemical-ionization mass spectrometry provides sensitive, rapid measurements but can be affected by isomeric contributions, fragmentation, and other ion-chemistry interferences, whereas gas chromatography (GC) provides molecular separation and specificity at lower temporal resolution. Here, we present a compact, low-power VOC measurement system that combines in-situ gas chromatography and thermal desorption (TD) preconcentration with a newly developed ultracompact proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) equipped with a novel vacuum-ultraviolet (VUV) ion source. The complete system occupies a 50 x 65 x 55 cm space, weighs < 70 kg, and consumes < 600 W of power during typical operation. The instrument combines high-time resolution, direct PTR measurements with periodic chromatographic measurements for regular molecular speciation. The system was operated continuously for 30 days in Thun, Switzerland with stable calibrant response (average variation of 3.5 %) during the ambient measurement period, with demonstrated direct-PTR limits of detection (LODs) of 13 – 136 ppt (1-min) and GC-PTR LODs of 0.1 – 4.0 ppt (1 L sample) across 11 calibrants. Together, these results demonstrate a complementary approach to instrument miniaturization in which reduced detector performance can be offset by upstream analytical separation and preconcentration. In this configuration, the direct PTR measurement provides high-time resolution observations, while periodic chromatographic measurements provide molecular specificity, sensitivity enhancement, and information on analyte-specific ion chemistry and interferences. By reducing the size, power requirements, and operational complexity, this system provides a pathway toward broader deployment of chemically specific VOC measurements at long-term monitoring sites, on mobile platforms, and in locations where infrastructure or reliable power is limited, to investigate emission sources, atmospheric processing, and the formation of secondary pollutants.
Competing interests: The authors declare the following competing financial interest(s): MSC, FLH, UR, VY, BML, DW, MC, and JJ are current or former employees of either Aerodyne Research or Tofwerk AG which manufacture and supply both the TD-GC systems and the compact chemical ionization mass spectrometer described in this work.
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