Determination of ultratrace amounts of copper(II) by its catalytic effect on the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline

A spectrophotometric method was developed for the determination of ultratrace amounts of copper(II) based on its catalytic effect on the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline to produce an intensely coloured dye (lambda(max)=525 nm) in the presence of hydrogen peroxide, In this reaction, pyridine acted as an effective activator for the catalysis of copper(II). By measuring the absorbance of the dye, copper(II) can be determined at the 0.002-0.1 ng cm(-3) (3.1x10(-11)-1.6x10(-9) mol dm(-3)) level. The relative standard deviation for ten determinations of 0.06 ng cm(-3) of copper(II) was 2.6%. The proposed method was successfully applied to the determination of copper(II) in tap water and biological material.