Quantitative determination of additives in a commercial electroplating nickel bath by spectrophotometry and multivariate analysis

Abstract

An electroplating nickel bath is usually composed of a number of organic additives to improve the plating process as well as to preserve its durability. Supreme Plus Brightener (SPB) and A-5(2X), used in a commercial electroplating nickel bath show highly overlapped UV-Vis spectra. These two additives are the only ones that present absorbance in the UV-Vis wavelength range. Therefore, a mixture of them can be resolved using multivariate calibration methods of UV-Vis measurements. In this work, Partial Least Squares (PLS) regression and Classical Least Squares (CLS) have been used to quantify both additives during the whole duration of an electroplating nickel bath. It was found that PLS regression provided the best results. To avoid negative influence of baseline drifts, first derivative spectra were used. Between 0.14 and 1.40 mL of the commercial product SPB per L of nickel bath can be determined with mean errors of about 6%. Between 4 and 24 mL of the commercial product A-5(2X) per L of nickel bath can be determined with mean errors of about 8%. The limits of detection (LOD) found for SPB and A-5(2X) were 0.11 mL L⁻¹ and 3 mL L⁻¹ respectively. The calibration models proved to be valid for at least eight months, including a change of spectrophotometer. The SPB concentration decays along the bath life according to a first order rate law, but A-5(2X) remains unchanged. Independent brightness measurements showed that it was intimately related to the SPB concentration, in such a way that any of them can be deduced from the other one. This is of prime importance to keep the bath conditions under control.