The colorimetric determination of copper in wine: total copper

Abstract

Background and Aims The total concentration of copper (Cu) in wine cannot be routinely measured without relatively expensive equipment, reagents and/or without labour‐intensive sample pretreatment. The following research describes an approach for the colorimetric measurement of total Cu in wine utilising a spectrophotometer and relatively cheap reagents. Method and Results The proposed method is based on using bicinchoninic acid as the complexing chromophore for Cu. Copper was measured directly and rapidly in white wine, while a digestion of red wine was required. A key step for the analysis in the non‐digested white wine matrix was the addition of silver(I) to aid the dissociation of Cu in the wine from sulfide. For red and white wines, the limit of detection was 0.02 mg/L Cu, and the repeatability was 3 ± 1%. The accuracy of the method was assessed in terms of recovery experiments (102 ± 3%, n = 4), and also by comparing total Cu concentration in 84 wines determined by the colorimetric method with that obtained by inductively coupled plasma with optical emission spectroscopy (R2 = 0.95). Conclusions The colorimetric determination of total Cu was successfully optimised and validated in white and red wines. Significance of the Study The methodology will allow wineries and researchers to routinely measure total Cu concentration in wine with a spectrophotometer.