Measurement of rainwater pH by optosensing flow injection analysis

Abstract

Optosensing flow injection analysis has been investigated as a technique for the determination of the pH of low ionic strength samples such as rainwater. Optosensing flow injection analysis (FIA) involves the use of a covalently bound reversible selective indicator on a cellulose substrate to detect a desired chemical species by reflectance spectroscopy. Effects due to potential metal ion interferences, variations in sample buffer capacity and carrier buffer capacity have been investigated. When using an FIA microconduit manifold, injected sample volumes are 75 µl with a carrier of 5 × 10^–4M acetate at a flow-rate of 0.8 ml min^–1. The range selected for the present purpose is from pH 3.5 to 5, with a precision of 0.0–0.11 pH over the range. Comparison of data obtained using the FIA system with conventional pH measurements by a glass electrode is presented. A sampling rate of 60 samples h^–1 was used.