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.