On-line Voltammetric Determination of Traces of Zn2+ in 105 Excess of Ni2+

Introduction: More than 20 ppm of Zn2+ impurities in Ni electroplating baths causes Ni coating anticorrosive and decorative properties degradation. The 105 excess of Ni2+ concentration however interferes the Zn2+ impurities quantification allowing correcting the Ni bath concentrations. Objectives: The objective of this work is the development, characterization and testing with real samples of a rapid and simple voltammetric method for automated on-line Zn2+ quantification in the presence of 105 excess of Ni2+. Methods: The proposed analytical method is based on the Zn2+ability to form soluble hydroxyl complexes in excess of OH-, while Ni2+ precipitates at these conditions. Zn2+ remaining in the liquid phase was determined by applying Differential Pulse Voltammetry (DPV). Results: The analytical characteristics of the developed DPV method were found to be the following: LOD 40 ppb; linear concentration range up to 32 ppm; relative errors from 2.21% to 8.74%. Conclusion: A voltammetric method for on-line automated Zn2+ impurities quantification in 105 excess of Ni2+ was developed, characterized, and finally tested with real industrial samples by comparison with ICP applied after Zn2+ extraction. The results deviation obtained by the two methods was less than 6.25% in the range from 3.2 to 14.7 ppm Zn2+.