Performance of stacked, flow-through micropreconcentrators for portable trace detection

Improving techniques for portable trace analyte collection and pretreatment is of critical concern for security, medical, food and environmental applications. The trend has been to employ MEMS technologies to meet this need as these microfabricated devices offer advantages such as small dead volumes, low power consumption, capacity for large scale manufacture and a commensurate savings with economies of scale. In this work a prototype trace sampling system intended for use with ion mobility spectrometers is presented. The system utilizes a stack of microfabricated preconcentrator plates capable of collecting samples in a sorbent polymer at flow rates up to 30 LPM. The plates are thermally desorbed after an integration period to produce a concentrated vapor plug that is transferred to the detector for analysis. A real-time controller, FPGA and custom electronics are used to manage independent heating of up to 4 of these devices in either constant voltage or temperature modes. The preconcentrators were tested with a commercial Vapor Tracer II IMS against TNT and RDX vapors ranging in concentration from 2.6 PPT to 620 PPT under a variety of conditions. Results are presented on performance of single preconcentrators with RDX, multiple cascaded devices vs. TNT and RDX, with and without a PDMS detector inlet membrane, and to compare sorbent coated and bare devices. The system demonstrated preconcentration factors of 38 with 2.6 PPT RDX and 30 with 13 PPT TNT.