Modified amperometric membrane probes for determining free and total residual chlorine in saline cooling waters

Modifications have been made to a Delta Scientific model 82124 free available chlorine probe so that it can be used to determine either the free or the total residual chlorine in cooling waters at coastal and estuarine power stations. For measurements of free residual chlorine, the internal filling solution of the probe was changed for one containing potassium bromide at pH 4. When the sample solution was dosed with potassium bromide and pH 4 buffer, the probe had a linear response over the range 0.04–1.0 μg ml^?1 Cl₂ and errors caused by changes in salinity were negligible. Total standard deviations for the analysis of 1.0 and 0.1 μg ml^?1 Cl₂ solutions were 0.055 and 0.01 μg ml^?1 Cl₂ respectively. For measurements of total residual chlorine a potassium iodide solution at pH 4 was used as the probe's internal filling solution and the sample solution was dosed with potassium iodide and pH 4 buffer. The probe had a linear response over the range 0.02-0.5 μg ml^?1 Cl₂, with total standard deviations of 0.05 and 0.01 μg ml^?1 Cl₂ at concentrations of 0.5 and 0.1 μg ml^?1 Cl₂ respectively.