Plating Solution Determined by Iodide Titration
Plating has been performed for centuries, and it is still widely used in modern industry for various purposes. Depending on the specific application, surfaces may be plated for decorative purposes, to provide protection against corrosion, or to enhance function. Instead of creating products entirely out of metal, manufacturers often use plating techniques to coat less expensive materials with a thin metal film. These techniques drastically reduce production costs, especially when the required materials are precious metals such as gold or palladium.
Depending on the intended function, type of metal, plating substrate, and several other factors, plating industries may employ a number of chemical and electrochemical deposition processes to apply metal coatings to surfaces. Many of these processes involve plating baths, which are solutions containing source ions of the metal being plated and other components such as buffering and stabilizing agents. To ensure the effectiveness of a plating solution, it is important to measure the concentration of the plating metal.
Several methods are available to analyze specific metals in plating solution. Among these, atomic absorption and emission spectroscopic techniques are highly accurate, selective, and can measure a wide range of concentrations. However, these methods require the use of expensive instrumentation. There are a number of gravimetric analytical methods, in which the metal is precipitated from the solution and weighed. For many of these gravimetric methods, the procedures are very intensive. Often involving boiling and filtration steps as well as the use of additional chemicals and external equipment, which can be costly, space limiting, and time consuming.
An alternative method for the analysis of metals in plating baths is titration. Many metals, such as copper, nickel, and zinc, react with EDTA and can be determined by complexometric titration. Gold and palladium react with iodide to form metal-iodide salts. Titrations provide accuracy comparable to gravimetric methods without the intensive sample preparation and are more cost-effective than atomic absorption and spectroscopy.
A customer contacted Hanna Instruments for a method to determine the concentrations of gold and palladium in their plating solutions. The customer was interested in a titration method that would be applicable for a wide range of concentrations of each metal. They were seeking an affordable solution which could be accommodated within limited benchtop space, while maintaining accuracy.
After determining that the other components of the plating solution would not interfere with the titration, a Hanna sales representative proposed the iodide titration method for the determination of both gold and palladium. The method could also be used for plating baths containing both metals by performing the titration twice; with and without the addition of citric acid. Citric acid acts as a masking agent for palladium to isolate the concentration of the gold ions. The palladium ion concentration could then be calculated by difference in volume between the two titrations. To perform the titration method, the Hanna sales representative recommended the Automatic Potentiometric (pH/mV/ISE) Titration System – HI902C with the Iodide Combination Ion Selective Electrode (ISE) – HI4111.
The customer was delighted that the titration could be performed with ease on the automatic titration system, and equally content that the automatic titration system, equipped with a burette with 0.1% dosing accuracy, could provide accurate results at an affordable cost. The customer was also pleased that the method could be customized to perform over a wide range of gold and palladium concentrations. The method called for a pH adjustment to 2.0 with nitric acid, so the customer was gratified that the pH measurement and adjustment could also be performed with the titrator, conserving benchtop space.