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  for Metal Finishing since 1989
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Testing Carbonate Levels

Does anyone know of a quick way of quantitively measuring carbonate levels in a potassium cyanide plating bath? The only technique I know of takes 1/2 day to a full day and I'm trying to find a quicker technique.

Mark Roberts
- England
2000

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This should be faster: Add a 10 ml sample of the bath to an erlenmeyer flask containing 100 ml hot DI H2O and 35 ml 10% Ba(NO3)2. Allow to settle, filter, wash filter 2X with hot DI H2O. Transfer precipitate and filter paper to a beaker, add 100 ml DI H2O, 5 drops methyl orange ⇦this on eBay or Amazon [affil links] indicator. Titrate with a standard HCl solution to a pink endpoint. oz/gal K2CO3 = (ml HCl) x (N HCl) x 0.921

James Totter, CEF
- Tallahassee, Florida
2000

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There is a similar procedure using BaCl2 in the Metal Finishing Guide Book. Instead of titrating with HCl I prefer the back titration procedure where you add a known amount of HCl and back titrate the unused HCl with NaOH. It is more accurate. Anyhow analysis with Barium should not take more then 30 minutes. (most of the 30 minutes is just to let the BaCO3 to settle).

Sara Michaeli
Tel-Aviv-Yafo, Israel
2000

The method that Sara lists is the one I prefer and that my laboratory has been using for over 30 years. It is quite accurate. I do however wish to make you aware that you should be performing the procedure under a hood (exhaust)

Gene Packman
process supplier - Great Neck, New York
2000

Fastest and easiest = spectrophotometry. A really easy to use and very accurate system can be obtained from the Hach Water Testing Company of Loveland Colorado. The actual test may take a minute or so, is extremely reproducible and can be accurate to less than a part per ten million. Pennies per test.

Dale Woika
- Bellefonte, Pennsylvania
2000