Process analytical chemistry in a nickel electroplating bath. Automated sequential injection for additive determination

Most of the useful parameters of a nickel electroplating bath can be monitored along the bath life. Process analytical chemistry (PAC) has been applied to follow parameters such as temperature, pH, chloride or nickel concentration. The monitoring of additives has special relevance because the final quality of finish depends on them. Two out of the four additives used in the commercial nickel bath used in this paper show UV absorption (A-5(2X) and SPB) and a sequential injection (SI) method has been developed to conduct and automatically dilute aliquots from the bath to a diode-array detector where UV spectra are acquired. Because the UV bands of the absorbing additives overlap, partial least squares (PLS) regression is used as a calibration method to resolve the mixture. A commercial software program has been used for the automated data acquisition. The program configuration and the SI manifold are given. The results obtained for additives are compared with those obtained from a manual method that is used as a reference. Mean random errors under 8% were always obtained. The limits of detection (LOD) found for A-5(2X) and SPB were 0.2 mL L-1 and 0.09 mL L-1 respectively. The SI methodology was applied with excellent results along a whole bath life and can be used to maintain the proper coating conditions.