Single fiber absorption measurements for remote detection of 2,4,6-trinitrotoluene

Single fiber optical measurements have been used to follow changes in the color of an initially clear poly(vinyl chloride) membrane as it reacts with aqueous 2,4,6-trinitrotoluene (TNT) to form a colored product that absorbs strongly at 500 nm. Attempts to make this measurement via the effect of the colored product on the emission spectrum of a fluorophore incorporated into the PVC membrane were unsuccessful. However, single fiber absorption measurements were successful. Refractive index matching to reduce stray light and a reflector behind the membrane to increase the reflected intensity were essential to keep the stray light levels small relative to the signal of interest. To compensate for drift, the reflected intensity at 500 nm is measured relative to the reflected intensity at 824 nm, a wavelength at which intensity is not affected by color formation in the membrane. The rate at which the ratio of reflected intensity at 824 nm to that at 500 nm increases is a function of TNT concentration. It is estimated that TNT levels as low as 0.10 mg 1^?1 can be determined by this technique.