On-line free-chlorine/total-chlorine monitors' evaluation - a step towards a correct choice of residual disinfectant monitor

Abstract

A number of commercially available on-line disinfection residual analysers were evaluated using a test rig under laboratory conditions. The methodology used for this trial was based on the following two standards: ISO Standard 15839 (2003), “Water Quality – On-line sensors/analysing equipment for water – Specifications and performance tests” and ISO 8466-1 (1990), and “Water Quality – Calibration and evaluation of analytical methods and estimation of performance characteristics. Part 1: Statistical evaluation of the linear calibration function”. The assessment of each analyser involved the determination of a set of performance characteristics including response delay, rise and fall times, linearity, limit of quantification and day–to-day repeatability. The effects of likely interferences were also covered. Results obtained from this trial for two total chlorine monitors were compared with the technical specifications as supplied by their respective manufacturers. This study concludes that persons responsible for instrument procurement should be cautious when relying only on manufacturers' technical specification claims. A more informed selection can be made by undertaking an evaluation study similar to the one described in this paper, as this will confirm the performance of a monitor under particular operating conditions. In general, residual disinfectant monitors utilising the colorimetric measurement method showed better performance than those employing amperometric/polarographic methods.