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There is a undetectable contamination in our analysis using a potentialstast

I am a research student at Indiana University we are doing analysis using a potenitialstat. We are looking for Cd, Cu, Pb, Zn. In the buffer solution when ran to attain the subtract there 4 peaks and at the beginning at about .05 volts there is a large decreasing slant. All precautions in preparing the buffer were taken yet still the contamination. One thing I can think of is we have to dry the sodium acetate because it is a mixture of the tri hydrate and the anhydrous so maybe in the drying process there could be some contamination from the oven. but a cover plate was used. We are using a polagraphic analyzer , and a mercury hanging drop electrode, the mercury has been in there for years. I am just looking for some input on where to look for the contamination.

Jermy Micheals
Indiana university - New Albany, Indiana, U.S.A
2004

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It is too long since I did any polarography and I have forgotten more than I knew. However, a few thoughts have come back. Firstly, I recall when I did it, the polarograms all had a slope to them and this was due to a capacitive current from the DME. Secondly, it was essential tht the mercury is clean and this was done by distilling it on a regular basis (lots of fun now, especially with current health and safety legislation!). Thirdly, the electrolyte must be pure, so use triple distilled water; do not use RO or DI water as this can pick up contaminants; obviously all water must be stored in clean glassware, not plastic. Fourthly, and I am not sure about this, but you are using divalent metals - is it possible that you are seeing a double reduction potential from one of them? It would help if you said what the potential of the stray peak was.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004