Kinetic photometric determination of copper at the nanograms per millilitre level in real samples

A highly sensitive and selective kinetic method is proposed for the determination of nanogram amounts of copper(II) based on its catalytic effect on the oxidation of 3-hydroxybenzaldehyde azine by potassium peroxydisulphase in an ammoniacal medium. The rate of the reaction is monitored spectrophotometrically at 465 nm and the method allows the determination of copper concentrations in the range 0.5–18 ng ml^?1 with a relative standard deviation of about 2%. The proposed method is virtually specific to copper and has been applied satisfactorily to its determination in a variety of food and industrial samples. A possible mechanism for the catalysed reaction is proposed.