Free chlorine analysers: a user's selection guide

Abstract

Selecting new instrumentation for integration into water quality monitoring programs is fraught with uncertainties and potential pitfalls. An evaluation methodology for assisting water managers and operators to make the correct choice of an online free chlorine (FC) analyser based on key performance parameters is presented. Eight amperometric and one colorimetric online FC monitors were evaluated against 15 metrological parameters (response, delay, rise and fall times, linearity, limit of quantification, day-to-day repeatability, the effect of interferences, etc.) according to the procedure outlined in the two standards: ISO Standards 8466-1 (1990) and 15839 (2003). The test results were compared with the analysers' technical characteristics supplied by their manufacturers. In general, colorimetric systems performed better than amperometric systems, with the latter experiencing significant interference from the pH of water which was not adjusted during tests. All analysers performed within manufacturers' claimed limits for some metrological parameters, whereas for other parameters their performance was not adequate. It is strongly encouraged to perform evaluation tests under conditions similar to those in the field before purchasing a monitor.