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A portable gas chromatograph–mass spectrometer (GC-MS) is an effective instrument for rapid on-site detection of volatile organic compounds (VOCs). Current instruments typically adsorb samples at ambient temperature, challenging the detection of low-boiling VOCs. In this study, a low-temperature adsorption thermal desorption method is proposed for sample enrichment in a portable GC-MS. The refrigeration module adopts a thermoelectric cooler (TEC), and a heating wire directly heats the adsorption tube to reduce the heat capacity. The miniaturization and low-power design make this module integrable into portable GC-MS devices. This module can reduce the temperature to around 0 °C within ten minutes for sample enrichment, and the heating system can increase the temperature to 260 °C within 20 seconds to ensure rapid desorption and injection of samples. Due to the miniaturization design, the total weight of the portable GC-MS is 21.7 kg, and the volume is 48 cm × 38 cm × 17 cm. Within merely 10 minutes, it completely separated and detected 65 VOCs in the TO-15 standard substance, with a detection limit down to 0.12 μg L−1 for toluene. The detection performance for low-boiling substances could be enhanced by up to 17 times compared to ambient temperature adsorption thermal desorption, such as 1,3-butadiene. Moreover, the results demonstrated long-term stability (RSD < 10% for 98% of the substances, with recovery rates from 91.66% to 109.12%). This study provides a feasible strategy for the rapid and reliable detection of VOCs in the air, holding great potential in the field of environmental monitoring. [ABSTRACT FROM AUTHOR]