ABSTRACT
This chapter focuses on the measurement of total or free residual chlorine in water, which can be measured by colorimetric, amperometric, or polarographic analyzers. Standard laboratory methods for determining aqueous chlorine concentrations involve iodometry in which free iodine liberated from potassium iodide is titrated with sodium thio-sulfate, using starch as an indicator. Various colorimetric procedures are available in which a colorless indicator is oxidized to a colored product, the color intensity of which is proportionate to the chlorine concentration. If chlorine is present in the water, a characteristic color develops with intensity in proportion to the amount of chlorine present. Amperometric analyzers are used in three basic forms: as titrators, as free residual chlorine analyzers, and as total residual chlorine analyzers. Periodic calibration is required through a separate determination of chlorine and is usually performed on a laboratory amperometric titrator using a standardized phenylarsine oxide solution. Microprocessor-based chlorine analyzers are available with built-in diagnostics and simulator features.
