An ion mobility spectrometer sensor system for subsurface use

An ion mobility spectrometer (IMS) probe system for real-time, subsurface soil-gas sampling applications is presented. The system includes an IMS and supporting electronics encased in a 51 mm diameter stainless steel probe housing. The IMS was challenged in the laboratory with 2,6-di-tert-butylpyridine (DtBP) and tetrachloroethylene (PCE) in zero air yielding reduced ion mobility constants (K_o) values of 1.42 cm²/Vs (n = 3) and 1.79 ± 0.01 cm²/Vs (n = 3), respectively. A resolving power of 38 and 31 was obtained for DtBP and PCE, respectively. The system was deployed at a PCE-contaminated site to demonstrate its performance under field conditions. PCE was detected in the vapor samples as evidenced by peaks with a K_o value of 1.80 ± 0.01 cm²/Vs for two measurements that were taken 6 min apart. The presence of PCE at the contaminated site was confirmed by GC-MS analysis of a gas sample at an EPA-certified laboratory, suggesting that this IMS system can be used to detect PCE under field conditions.