Simultaneous determination of pH, chloride and nickel in electroplating baths using sequential injection analysis

A sequential injection analysis system was developed to quantify pH, chloride and nickel in electrolytic baths, in the ranges 1-5 pH units, and 0.1-1.0 and 0.1-1.6 mol l⁻¹, respectively. To enable pH and chloride determination, potentiometric detection with two ion-selective electrodes in a tubular configuration was used. Nickel concentrations were assessed using colorimetric detection at 660 nm. pH was determined prior to nickel determination and just after sample injection (500 μl) into a 0.025 mol l⁻¹ phosphate buffer carrier stream at pH 6.3 and a 9.10 ml min⁻¹ flow rate. For chloride determination, on-line dialysis through a cellulose membrane was used to enable sample dilution and matrix separation. A 2⁵⁻¹ fractional factorial design based on the carrier solution composition and the levels of the hydrodynamic parameters was used for system optimization. At the optimized settings a sampling rate of 40 samples h⁻¹ was attained, with precision and accuracy statistically indistinguishable from those achieved with conventional procedures.