POLYMER-COATED, TAPERED CYLINDRICAL ATR ELEMENTS FOR SENSITIVE DETECTION OF ORGANIC SOLUTES IN WATER

Commercially available tapered chalcogenide fibers have been coated with poly(vinyl chloride) (PVC) plasticized with 47% (w/w) chloroparaffin containing 60% CI by weight. The coating procedure involves applying a drop of a solution containing PVC and the plasticizer in tetrahydrofuran along the fiber while allowing the solvent to evaporate. The coated fibers were exposed to 0.15% (v/v) benzene in water (1479-cm(-1) band), 0.40% (v/v) chloroform in water (1216-cm(-1)), and 0.10% (v/v) nitrobenzene in 1.5% (w/v) methanol/water (1348-cm(-1)). All three organic solutes gave readily detectable signals with the coated fibers but were not observable when the aqueous solution was sampled with the use of an uncoated, tapered fiber. Detection limits for benzene, chloroform, and nitrobenzene were calculated to be 0.02%, 0.11%, and 0.006% by volume, respectively. These data show that the advantage of using a polymer coating to concentrate the analyte and reduce the water background may be combined with the advantages of using a tapered optical fiber to yield a sensitive method for detecting nonpolar organic solutes in water.