Selective detection of organophosphate nerve agents using microplasma device

Abstract

A direct current glow discharge microplasma source permits ambient ionization directly and can provide fast and accurate in situ detection combined with a spectrometer. In this study, a stable microplasma-based detector for nerve agent detection has been developed. The innovative concept of this new nerve agent detector is to detect two parts of the nerve agent components, the element phosphorus and the organic part, CH radicals, at the same time. Because there are two detection targets, our microplasma-based detector has enhanced selectivity for nerve agents. The reasons for this characteristic are studied through comparing the emission spectra of the microplasma and microwave plasma. We suggest that it's the very low gas temperature of our microplasma source that makes it possible to excite the nerve agent molecules without decomposition or splitting of the CH component. Thus the spectrometer can detect the emission lines of the element phosphorus and the organic CH radicals simultaneously. The influence of discharge current and gas flow rate on phosphorus signal intensity has been investigated. The emission intensity of phosphorus at 253.6 nm increases linearly with the discharge current in our tested range, but non-linearly with the gas flow rate. The detection curve has been calibrated. The emission intensity at 253.6 nm is in proportion to the concentration of the specimen triethyl phosphate (TEP) in the range from 41 ppm to 500 ppm by volume. The detection limit was calculated to be 5 ppm by volume. Small size, low power, low cost, and high selectivity make our device very suitable for nerve agent scanning in the field.