On-Line Determination of Succinate Anion in Zinc Plating Baths: A Comparison of Methods

rocess and quality control are exP tremely important in achieving optimum production and they have a special place in continuously operating processes. Real-time process monitoring is the comerstone of maintaining an efficient electroplating process. For the steel industry, zinc and nickel electroplating processes used for anticorrosion treatmentl must be monitored to maintain certain standards such as suitable electrolyte levels and uniformity of composition of electrolyte, degeneration of raw materials, consumption evaluation, pollution from product recycling, chemical stability, yields, etc. The determination of metals in electrolytes does not pose substantial difticulties. Atomic spectroscopy, FRX, coulometry or electroanalysis are generally used. The on-line determination of anions is more difficult, owing to the high salt concentration of the matrices, especially when high sensitivities are required for estimating the f2% variation demanded in the design of the process. Most electrolytes contain the following major anions: chloride, sulfate, succinate, acetate, silicate, cyanide, phosphate, borate, fluoborate and citrate.2 Because classical analytical techniques are not satisfactoly, these anions must be controlled indirectly through batch procedures, yielding unreliable results. The determination of succinate is an interesting challenge from a technological point of view. This anion must be determined in the zinc electroplating process in the on-line manufacturing of galvanized plate (similar to processes used in the steel industly). Because high temperatures (>60°C) are required to maintain the electrolyte fluid and a strong reducing medium is also necessary, major losses of this anion are unavoidable. Thus, its content (approximately 10% by volume) must be