Limits of detection of explosives as determined with IMS and field asymmetric IMS vapour detectors.

Performance of two handheld trace explosives detectors types: SABRE 4000 and MO-2M was compared in terms of the limits of detection determined for: trinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine, pentaerythritol tetranitrate and nitroglycerin in the particle detection mode. SABRE 4000 detector is a conventional detector based on the ion mobility spectrometry (IMS) and radioactive nickel as the ionization source, whereas in the MO-2M type detector a variant of this technique, viz. the field asymmetric ion mobility spectrometry (FAIMS), and a different β emitter, tritium, as an ionization source are employed. In determining limits of detection the sampling technique was suggested which resorts to binomial distribution for the determination of the indispensable number of positive measurements required to regard a given amount of explosives detected as reliable. Lower limits of detection were achieved in the study for trinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine with the MO-2M detector (10- and 100-fold, respectively) than with the SABRE detector, whereas for the remaining two substances limits of detection were identical for either detector. The results obtained were discussed in the aspect of the effect of the detector design, ionization mechanism and volatility of substance as the factors that determine the limits of detection values.