Determination of Organic Compounds by IR/ATR Spectroscopy with Polymer-Coated Internal Reflection Elements

Abstract

The possibility of quantitative determination of organic compounds in aqueous solution or in the gaseous phase by FT-IR/ATR spectroscopy by the aid of polymer-covered internal reflection elements has been studied. In general this method has three effects: (1) exclusion of water from the measurement, (2) lowering of the limit of detection because of the continuous and reversible enrichment of organic compounds, and (3) reduction of the half-width of the absorption bands for gases by insertion of the molecules in a polymer film. The enrichment of some halogenated hydrocarbons in three different polymer materials was used to determine the concentrations of these substances in water by IR spectroscopy with very good limits of detection (sometimes less than 1 mg/dm3). In all cases a linear relationship between concentration of the sample and apparent extinction of the absorption band of interest is recorded. The time constants for 90% saturation of the polymer are several seconds for measurements of gases and some minutes for aqueous solutions, depending on the polymer material and the character of the substance.