Benzoic acid ͑BA͒ and benzylidene acetone ͑BDA͒, together with polyethylene glycol, are used as additives in electroplating zinc baths. The simultaneous BA and BDA determination is proposed by applying partial least-squares regression to the ultraviolet ͑UV͒-visible spectra between 216 and 350 nm. Concentrations between 1.02 and 10.2 g L −1 BA and 0.100 and 0.550 g L −1 BDA can be determined. Several proposals to estimate the multivariate limit of detection ͑LOD͒ have been applied, including the use of the net analytical signal, found vs added plots, and the use of multivariate standard deviation. Depending on the method used, the values of LOD found the range between 0.1 and 0.4 g L −1 for BA and 0.01 and 0.03 g L −1 for BDA. The multivariate method has been applied to follow BA and BDA concentrations along a Zn bath life. BA concentration remains practically unchanged, but BDA concentration continuously diminishes by degradation on electrodes and by evaporation. There is a direct relation between BDA concentration and brightness of the plated piece. Thus, the proposed method can be related to brightness.

The use of proton nuclear magnetic resonance ((1)H-NMR) for the quantification of additives in an electrolytic Zn bath is reported. A simple and quick method is described that does not need any prior sample preparation. Contrary to other analytical methods, the three additives in the bath, benzylidene acetone (BDA), benzoic acid (BA) and poly(ethylene glycol) (PE400), can be quantified. Two calibration methods were tried: integration of NMR signals with the use of an internal standard and partial least squares (PLS) regression applied to the characteristic NMR peaks. Both methods are compared and the univariate method was preferred because of simplicity, accuracy and precision. The following limits of detection were found: 0.30 g L(-1) BA, 0.08 g L(-1) BDA and 0.7 g L(-1) PE400 with dynamic ranges of at least 1.0-6.0, 0.1-0.6 and 3.0-18.0 g L(-1) respectively. Those concentration ranges are suitable to follow the concentration of additives in the bath in real time. (1)H-NMR spectra provide evidence for the BDA degradation pattern.

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Process analytical chemistry (PAC) is applied to a zinc electroplating bath to monitor the concentration of benzylidene acetone (BDA) and benzoic acid (BA) additives. BA tends to maintain its concentration during the use of bath but BDA degrades according to a first-order law causing the bath to function improperly. The methodology includes the use of sequential injection (SI) as a flow method to automatically conduct samples of bath to a diode-array UV detector for spectra acquisition after proper dilution. Dedicated software has been developed using the LabVIEW environment for the control of a multiburette and selection and injection valves. The software is available on request. The UV signal is used to develop a partial least squares (PLS) calibration model that can resolve the mixture of additives. Mean calibration and validation errors for BDA and BA under 3.7% and 5.2% respectively were found. The results do not differ significantly from those obtained with a manual method used as a reference. Excellent results were obtained when the automated method was applied along a whole bath life and it can be used to maintain the proper plating conditions.