Abstract
Abstract The stannous chloride reduction procedure for the colorimetric determination of total phosphorus in wastewater samples using potassium persulphate digestion was evaluated. Samples with salinities as low as 50 mg/1 gave phosphorus levels approximately 10% lower than the true levels when absorbance readings were taken after the recommended time interval of 10 minutes. With increasing salinity, the error increased to approximately 20%. This error can be overcome by the addition of sodium chloride to both standards and samples to achieve salinity levels of 2,000 mg/1 or greater, and making absorbance measurements after allowing at least 2 but not more than 3 minutes for colour development.
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