Introduction
The analysis of organic additives in electroplating baths by cyclic voltametric stripping (CVS) is a robust method and widely used in the electroplating industry. To ensure that continuously reliable results are obtained standardized daily operation procedures are of highest importance. They all contribute to keep the measuring system at best performance.
This document acts as a guideline through the working day. Procedures are described, which should be carried out when starting up the system, during the working day and when the system is shut down. Further general recommendations and procedures, which do not have to be carried out on a daily basis are described.
The recommendations and descriptions in the following refer to the analysis of acid copper plating baths. For the analysis of other plating baths, e.g. tin, tin/lead or electroless copper plating baths some recommendations may not apply.
Procedures During the Working Day
The following points should be considered throughout the working day.
Dosing Units
-
Actions
Prepare a dosing unit twice each time a new solution is used.
-
Comments
When a dosing unit has to be filled with a different solution, e.g. a sample for the suppressor determination, different VMS or another additive concentrate the dosing unit has to be thoroughly rinsed with the new solution.
If possible, the preparation should be done without the measuring vessel below the measuring head and using port 3 for waste. A beaker can be placed below the measuring head.
Rinse electrodes and tubing thoroughly with deionized water after preparation to avoid carryover.
Temperature
-
Actions
Make sure to maintain a stable temperature throughout the working day and during determinations. Plating baths are often operated at elevated temperature, e.g. 50 °C. Thus, samples have to be left to cool down prior to the analysis, especially when high volumes are used.
-
Comments
Letting a fresh plating bath sample cool down is especially important for determinations, where a high sample amount with respect to the total volume in the measuring vessel is used. This is the case in brightener determinations by LAT or MLAT or some leveler applications.
For determinations using an external calibration curve (dilution titration, response curve) it is important that the temperature of the measuring solution during calibration does not significantly differ (<5°C) from the temperature during determination.
The measuring system should not be exposed to direct sunlight or placed below an air conditioner.
Measuring vessels with a thermostat jacket can be used in combination with a water bath circulator to ensure a stable temperature.
Solution Addition
-
Actions
During a determination the electrodes must not be removed from the measuring solution. Additions which are done after the initial conditioning in a method have to be done via the pipetting opening. The measuring head must not be lifted during a determination for this purpose.
-
Comments
Keeping the electrodes immersed in the solution throughout a determination is important to maintain their conditioned state and to obtain reproducible and stable measuring curves.
At the very beginning of a determination the solutions can be added with opened measuring head. At this time the electrodes are not conditioned yet for the respective application.
Shut Down Procedures
The following procedures should be carried out when the system is not used for a longer period of time, e.g. overnight.
Reference Electrode - RE
-
Actions
Replace the electrolyte in the reference electrode every second to third day. This should be done at the end of a working day, when shutting down the instrument, to allow sufficient time for equilibration of the reference potential.
-
Comments
After replacing the electrolyte allow at least 4 hours for the reference potential to equilibrate. Refilling the reference electrode at the end of the working day gives the electrode potential sufficient time for equilibration.
Care should be taken that no air bubbles are present at the diaphragm or around the AgCl cartridge to avoid contact problems.
More information on how to handle the reference electrodes in voltammetry can be found in our multimedia guide (A.717.0003).
If the maintenance free electrode (6.0730.000/6.0730.100) is used, no actions are necessary.
Electrode Storage
-
Actions
If the electrodes are not used for a short time, e.g. a few hours, they can be left in the measuring vessel immersed in deionized water.
If the system is not used overnight or for a longer time, the electrodes have to be stored separately. The reference electrode assembled with the bridge electrolyte vessel is taken out of the measuring head and stored in a separate vessel (e.g. 6.2008.040 or 6.2743.057). The storage vessel has to be filled with deionized water or a solution of c(KNO3) = 1 mol/L. The bridge electrolyte vessel should be filled with c(KNO3) = 1 mol/L to the mark prior to storage. The working electrode and the auxiliary electrode can be stored dry.
-
Comments
More important than the used storage solution for the reference electrode is that the reference electrode does not run dry. A storage vessel should be used, where the solution cannot evaporate.
In a fully automated system, it is not possible to store the electrodes individually at the end of a determination series without human interaction. In this case the measuring vessel should be filled with deionized water after the last determination. The measuring vessel must not be emptied after a determination series because the reference electrode will dry out. The electrodes should furthermore not be stored in VMS or in the measuring solution.
If the completely maintenance-free reference electrode (6.0730.000, 6.0730.100) is used, it is recommended to store it in c(KCl) = 3 mol/L, when the instrument is not in use. Under no circumstances may the reference electrode dry out as this will destroy it irreparably.
Dosing Units
-
Actions
Prepare the dosing units with deionized water at the end of the working day and leave dosing units filled.
-
Comments
Preparing the dosing units with deionized water prevents blockage due to crystallization.
Do not empty the dosing units with the «Empty» function for storage overnight. Otherwise, small residual amounts of solution will remain inside the cylinder, tubing and other compartments of the dosing unit. Then crystallization will occur more easily due to facilitated water evaporation.
If the dosing units are not used for a longer time (e.g. a week or longer) they should be disassembled, rinsed and left to dry. After drying they are reassembled and stored dry.
Additional Support
If you encounter any issues or need additional help, please submit a support ticket through Metrohm Technical Support.
For additional training on any of these topics, explore our Metrohm Custom Training options.