For most explosives vapor detection scenarios, the lower detection limit (LDL) requirements are at part-per-trillion (ppt) concentration levels. Further sensitivity constraints are imposed on the detector modules by attendant sampling dilution and inefficient transport of explosives vapor molecules through the detection system sample train. Efficient transport and large preconcentration factors (≃ 100,000) can be achieved simultaneously by using a liquid sampling module, comprising a wetted-wall column in the sample train. Liquid sampling modules are interfaced most effectively to wet-chemical detectors. The transport and preconcentration processor introduces a 60-s or longer lag to the overall system time rate-of-response depending on the preconcentration requirements. Despite the long delay time of liquid preconcentrators and the relatively slow rate-of-response time and limited sensitivity of wet-chemical vapor detectors, it appears that their use is feasible for some applications. For example, those detectors with a liquid transport and preconcentration sample train can monitor the atmosphere within enclosures such as rooms, buildings, etc. The inlet to the sample can be located at some convenient and effective point, e.g., in the main air conditioning or ventilation duct upstream of the blower.