How to check the gold concentration in a gold plating bath?

A. Kyna,

Other than AAS to analyse gold, sulfuric acid method is the best.Try this method with the following procedure.

Take required sample of the plating solution in a conical flask and add 30 to 50 ml of sulfuric acid.Heat well and when you notice sulfuric fumes (it may take 30 minutes) allow the sample to cool. Now slowly and gradually add hydrogen peroxide till you get a clear solution and heat it to evaporate excess peroxide.Filter the precipitate and weigh the gold.

Apart from this method gold can be analysed by volumetry and by using Faraday's Law. But the above method is the easiest.

Q. Dear VENKATA ,

Thanks for you reply and it really helps me a lot. By the way, I would like to know whether I can get the weight of the gold without the filtration process? Since I find filtration needs quite a long time and the filter paper is easily corroded by the H2SO4. Also, would you mind to tell me why H2SO4 can recover the gold sponge, what is the exact reaction behind it?

Thank you very much,

A. Dear Kyna,

The problem you are facing in filtration process is the dissolution of filter paper by sulfuric acid I believe. If that is your problem it can be taken care of. Filter paper dissolves in sulfuric acid because it's concentrated and hot. Dilute the sulfuric and then cool the conical flask. Now filter. You won't face any problem. (Be careful while diluting) As far as chemical reaction is concerned it's just a reduction process. sulfuric acid reduces the Au from the solution.