Catalytic Kinetic Determination of Silver through its Catalytic Effect on Congo Red-Peroxodisulphate Reaction

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A kinetic-spectrophotometric procedure is reported for determination of trace amounts of Ag(I). This method is based on catalytic effect of silver ion on the oxidation of congo red by potassium peroxodisulphate at pH=3.4 and 30 oC in the presence of 1,10-phenanthroline as an activator. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance of congo red at 510 nm in the range of 30-330 seconds after initiation of the reaction. Silver can be determined in the range 2-100 and 100-1100 ng/ml with detection limit 1 ng/ml. Ten replicate analysis of a sample solution containing 8 ng/ml silver gave a relative standard deviation of 1.0%. This method was used for determination of silver in water and photographic plate samples.