Gas chromatography with flame ionization detection for determination of additives in an electrolytic Zn bath.

The monitoring of additives in electrolytic baths is a fundamental task for proper coatings. Among the additives used in zinc baths, benzylideneacetone (BDA), benzoic acid (BA) and polyethylene glycol 400 (PEG400) are easily found. This paper deals with the possibilities of handling the bath sample before it is taken to a gas chromatograph (GC) in order to follow the additives concentration along the bath life. The applied techniques include solid phase extraction (SPE), solvent extraction (SE), static headspace (SHS), direct injection (DI) and headspace solid phase microextraction (HS-SPME) recoveries up to 6:1, 14:1, 9:1, 1:1 and 80:1 respectively have been obtained. Internal standards have been found for every case. Advantages and disadvantages of the techniques are collected. In this paper DI and HS-SPME have finally been applied, though none of them is able for PEG400 determination. DI provides quantitative information for BA (limit of detection, LOD, 1.6 gL(-1)) and BDA (LOD, 0.09 gL(-1)); HS-SPME only provides quantitative information for BDA (LOD, 0.05 gL(-1)). Taking into account that PEG400 and BA do not practically change with the use of the bath, that DI is very quick and simple and that no significant differences with spectrophotometric results have been found, DI is recommended for the monitoring of BA and BDA along the zinc bath life. This should be considered a technique for process analysis for these additives.