Volumetric control of an electrolytic engraving process. Analysis of mixtures of hydrochloric acid, phosphoric acid and aluminium

The volumetric determination of hydrochloric acid, phosphoric acid and free aluminium in electrolytic engraving bath samples is described. Three consecutive acid-base volumetric measurements were performed, using a commercial combined pH sensor to determine the equivalence volumes of each titration. Sodium fluoride was used to mask the interference of free aluminium in the quantification process for both acids, optimizing the amount of masking agent necessary for quantitative results. The results, evaluated through the preparation of synthetic samples, show good reproducibility (RSD 1%). The relative error associated with the method was less than 3%. The method presented here facilitates the analytical control of the electrochemical engraving bath in the manufacture of offset printing matrices, verifying its function and allowing the optimization and control of the production process.