Sensing of chlorinated hydrocarbons and pesticides in water using polymer coated mid-infrared optical fibres

Abstract

An IR fibre optic sensor which operates in the 4–16 µm wavelength region has been developed for the in-situ monitoring of chlorinated hydrocarbons and pesticides in water. The sensing element consists of a silver halide (AgCl_xBr_1–x) optical fibre, coated with a polymer which both enriches the analyte in the evanescent wave region of the fibre and, when thick polymer coatings are used, minimizes water interference in the IR absorption. Using trichloroethylene and alachlor as representative pollutants, evanescent wave spectrometry in the mid-IR region is shown to provide good performance down to single ppm levels. Furthermore, it is shown that the technique can be applied to multi-analyte samples.