Online monitoring of volatile organic compounds in water by ultra-low-temperature purge-and-trap coupled with gas chromatography-mass spectrometry system

Background Volatile organic compounds (VOCs), ubiquitous aquatic pollutants, have garnered global attention due to their potential threats to aquatic organisms and human health. While purge-and-trap (P&T) with gas chromatography-mass spectrometry (GC-MS) is the standard detection method, commercial systems face limitations in detection limits and contamination resistance due to sorbent traps. This study developed an adsorbent-free ultra-low-temperature P&T system using Stirling cryogenic refrigeration technology, integrated with fully automated online sampling and quality control modules, thereby establishing a robust GC-MS monitoring platform. Results The developed system achieves quantitative VOC capture at −120°C without adsorbent materials, eliminating trap degradation and cross-contamination. Comprehensive validation using 56 representative VOCs demonstrated exceptional analytical performance in full-scan data acquisition mode: linear dynamic range of 0.1–10 μg L −1  (R 2  > 0.9975), method detection limits (MDLs) of 0.005–0.016 μg L −1 , precision of 2.0–5.2% (RSD, n = 6), and trueness of 86.9–115.7% (recovery). A 15-day continuous field validation in real drinking water sources confirmed system robustness (recoveries ranging from 70.0% to 130.0% for 94.6% of all target compounds). Significance This adsorbent-free approach differs from conventional adsorption-based methods by relying on condensation for VOC enrichment. It achieves detection limits more than five times lower than China's standard GB/T 5750.8-2023 method (0.055-0.365 μg L −1 ) while avoiding carryover contamination and adsorbent-related maintenance. By eliminating consumable trap packing and supporting autonomous operation through integrated QC protocols, the system reduces operational costs and personnel requirements. These characteristics make the technology suitable for unattended, long-term online monitoring in complex environmental matrices, providing a practical option for real-time surveillance of hazardous VOCs in remote water sources and facilitating rapid response to episodic pollution events.