Determination of Trace Amounts of Copper(II) by Using Catalytic Redox Reaction between Methylene Blue and Ascorbic Acid

Abstract

A sensitive and selective kinetic-spectrophotometric method is proposed for the determination of µg mL^-1 amounts of Cu²⁺ based on its catalytic effect on the oxidation of L-ascorbic acid by Methylene Blue in a strongly acidic medium. The reaction is monitored spectrophotometrically by measuring the decrease in color intensity of Methylene Blue at 665 nm. The analysis of Cu²⁺ ion is performed by a fixed-time method. At a given time of 2 min at pH 2.20 and 32°C, the detection limit is 10 ng mL^-1 and the relative standard deviation for 0.4 µg mL^-1 Cu²⁺ is 3.60% (n = 6). The method is free from most of the interferences and the effect of diverse ions on the determination of Cu²⁺ is also reported. The proposed method is virtually specific to copper and has been satisfactorily applied to its determination in electric copper wire samples and pharmaceutical products. Results were also verified by the atomic absorption spectrometry technique (AAS).