Micro-particles as interfering substances in colorimetric residual chlorine measurement

Conventional methods using o-tolidine and N,N-diethyl-p-phenylenediamine as colorimetric reagents have been extensively applied worldwide in residual chlorine measurement for water quality and environmental management. Different types of interferences resulting in erroneous measurements while using colorimetry have been previously reported. In this study, we experimentally demonstrated micro-particles as interfering substances in selected inorganic (five metal oxidants) and organic (microalgae) particles. The results indicated erroneous measurements (viz. colour development) for three of the selected particles. These erroneous measurement levels were evaluated with reference to the chlorine concentration (in mg-Cl₂/L, hereafter represented as mg/L) in relation to both representative colorimetric reagents in terms of the amount of particles and time variations. A novel viewpoint that filtration could be a possible solution to the erroneous measurement caused by such micro-particles was proposed.