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Measuring Ag concentration in Immersion Silver bath

2007

We are small Printed Circuit Board production company located in Lithuania. Recently we obtained AlphaSTAR(tm) immersion silver plating line. I am interested in silver plating bath maintenance. Technical data sheet says, that we should measure Ag concentration by Atomic Absorption Spectroscopy ⇦this on eBay or Amazon [affil links] . Unfortunately we can not afford AAS device, so I'm looking for alternative method.
Two options cross my mind: Ion Selective Electrodes (ISE) and conductometric titration of silver bath solution. Negative side of ISE method is that AlphaSTAR(tm) Silver may contain organic compounds, which may spoil ion-selective electrode membrane. How should I remove those organic compounds?
Is the conductometric titration with HCl proper way to determine silver concentration? According to theory, Ag ions and HCl should form non-conductive and insoluble in aqueous solution salt.
Thank You.

Povilas Reskevicius
plating shop employee - Kaunas, Lithuania

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2007

What's the matter with doing it the way we do it in a standard plating bath?

If it's a cyanide based solution, add about 3 ml 30% hydrogen peroxide to 20 ml of solution in a 500 ml Erlenmayer, and let it stand. After a few minutes, there will be a very obvious reaction. This step is to destroy most of the cyanide, rather than blowing it off as HCN.

Now add about 10 ml each nitric and sulfuric acids. With VERY GOOD VENTILATION. Now, heat to dense white fumes. Let it cool, then dilute it up to about 100 ml with water. Add a few drops of ferric sulphate or ferric ammonium sulphate. Now, titrate it to a pink endpoint with 0.1N potassium thiocyanate ⇦this on eBay or Amazon [affil links] solution.

The Ag+ and the SCN- combine in a 1:1 ratio to form the white solid that precipitates. Once all the Ag+ has reacted, you start to get ferric thiocyanate, which signals the endpoint.

Dave Wichern
Consultant - The Bronx, New York