The Electroanalytical Detection and Determination of Copper in Blood: Ultrasonically Enhanced Solvent Extraction Coupled with Electrochemical Detection by Sono-Square-Wave Stripping Voltammetry Analysis

Abstract

Solvent extraction of copper using the N-benzoyl-N-phenyl-hydroxylamine ligand was employed as sample preparation for the sono-square-wave anodic stripping voltammetric (sono-SWASV) determination of total copper in diluted laked horse blood. The methodology involved sono-emulsification of the target aqueous phase with the ligand dissolved in ethyl acetate. Copper is then recovered into a fresh “clean” aqueous phase by emulsification with acid which “back-extracts” it from the organic phase. During emulsification ultrasound is helpful in maintaining a high surface area of organic to aqueous phase in contact enabling extraction to take place at 25 °C. Ultrasound also facilitates the liberation of copper from the active sites in which it is bound ensuring that slow release of bound copper from the protein ceruloplasmin does not compromise the results. During the deposition step of the analytical sono-SWASV ultrasound was effective in maintaining a clean electrode by cavitationally removing any residual ethyl acetate from the vicinity of the surface. Acoustic streaming and cavitation promoted the mass transport of copper to the surface of the electrode, facilitating measurements in solutions of low copper concentration, where silent measurements failed to yield an analytical signal. The methodology presented within required a sample volume of 100 μL giving a total copper determination of 1613 μg L−1 with a standard deviation of 25 μg L−1. The limit of detection for the clean test medium obtained using solvent extraction, 0.16 μg L−1, suggests that even lower sample volumes can be quantitatively interrogated with a pinprick test not unfeasible.