TOC Determination in Electroplating Bath Solutions by UV Digestion Application Note · multi N/C UV HS

Introduction

Electroplating baths are widely used to deposit a metal coating on a conductive surface by immersion of the objects into a bath solution and application of an electric current. The purpose of this can vary in a wide range that includes decorative silver, gold, or palladium finish on jewelry or the enhancement of physical properties such as corrosion prevention, conductivity, hardness, or durability changes to materials. Manufacturers of plating baths need to establish optimum specifications for their plating solutions and must take action to maintain their formulations and to prevent problems related to improper levels of bath constituents and contaminants. Among other parameters, gradual and continuous changes in cyanide or surfactant content of plating baths may lead to a significant decrease in efficiency. All these problems can be addressed and avoided by monitoring the sum parameter TOC in quality control of plating bath production.

There are two very common principles that can be applied for TOC determination in liquid aqueous matrices: catalytic high temperature combustion and wet chemical digestion promoted by UV light and additional chemical oxidants.

Wet chemical UV digestion is the principle of choice for very aggressive matrices like high salt and/or sulfuric acid concentrations. While the metal salts and mineral acid concentrations may quickly damage the combustion tube and catalyst in catalytic combustion TOC methods, the big advantage of UV digestion is a minimum of maintenance and wear of the TOC system.

The oxidation power of the multi N/C® UV HS that was used for these measurements is very high due to its high-power, longlife UV reactor. Hence, a complete oxidation of the organic compounds inside the sample is ensured. By application of a TOC differential method, not only the total organic carbon but also the total inorganic carbon (TIC) can be analyzed. It has to be mentioned that inorganic carbon such as cyanides are by definition analyzed as TOC, since the TIC is defined to be the carbon bound in carbonates and hydrogen carbonates which release CO2 under acid treatment.