Into an aliquot containing 112.4 μg/25 ml of Cd(II), 5 ml of 1×10−4 mol l−1 solution of PAR and 2.5 ml of 1 mol l−1 NaClO4 were added. After mixing with the appropriate amount of pure ethanol, the pH of the solution was adjusted to 5.5 with dilute HClO4. The resulting solution was filled up to 25 ml with deionized water and the absorbance was measured at 510 nm against a reagent blank similarly prepared and of the same pH as the test solution but containing no Cd(II).