MSFIA-spectrophotometric method for the determination of additives in electrolytic Zn baths

A. Barriola, M. Ostra, C. Ubide, J. Zuriarrain

Dpto. Quimica Aplicada, Univ. País Vasco, San Sebastián. E-mail:

Benzoic acid (BA) and benzylidene acetone (BDA), together with polyethylene glycol (PEG400), are used as additives in electroplating zinc baths. The mechanism by which BDA acts has already been studied, showing that deposits formed in the presence of BDA are softer. However, in electrolytes containing benzoic acid and/or non-ionic surfactants, such as PEG 400, BDA seems to be worn away during zinc electrodeposition, mainly due to electrochemical reactions at the cathode. Therefore, it is of great interest to develop analytical methods which allow to determine the concentration of these additives in zinc baths and to control their degradation in order to assess the effect of this degradation in the change of the properties of bath and in the final coating properties.

UV-Visible spectrophotometry has recently been used as a suitable technique to predict BA and BDA concentrations in acidic Zn baths [1]. The proposal of this communication is the application of multisyringe flow injection analysis (MSFIA) in order to get an automated method for the simultaneous spectrophotometric determination of BA and BDA in electrolytic Zn baths.

Figure 1. Automation device for BA and BDA determination in an electrolytic Zn bath.

For the present communication a weakly acid zinc bath has been used containing ZnCl2, KCl, H3BO3 and methanol as matrix; and BA, BDA and PEG400 as additives. Figure 1 shows the MSFIA automation device used for the measurement of UV-Visible signals. Partial least squares regression (PLS) was applied to absorption spectra between 216 and 350 nm. Concentrations between 0.1 and 0.6 g L-1 BDA and 1 and 6 g L-1 BA can be determined. Two latent variables (LV) were used for both BA and BDA with relative errors lower than 6% in all cases.

The automated method has been applied to follow BA and BDA concentration along a Zn bath life. Similar results were obtained when compared to those provided when the manual spectrophotometric method was applied.

[1]  A. Barriola, E. García, M. Ostra, C. Ubide, J. Electrochem. Soc. 155 (2008) D480-D484.