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Use of Fluorescein Indicator





September 30, 2010

Hey guys I have been out of the plating industry for a few years, but recently have gotten back in. At my previous place of work we used dichloro-fluorescein in our lab it seemed like to find nickel chloride or nickel sulfate concentrations. I don't recall does anybody know what the test is? I really wish I kept the lab manual I created 5 years ago.

Jason D
Lab Tech - Grand Rapids, Michigan



First of two simultaneous responses -- October 1, 2010

We use it for determination of nickel chloride in our nickel baths.

5 mL bath sample
1 mL dichlorofluorescein (2% solution in ethanol)
titrate with 0.1N silver nitrate to a cloudy tan endpoint. (I just look for the disappearance of the green color)

nickel chloride (oz/gal) = mL's used x 0.319
nickel chloride (g/L) = mL's used x 2.4

Hope that helps.

Geronimo Cebrero
- Oxnard, California, USA



Second of two simultaneous responses -- October 1, 2010

Hello, Jason. You would have been doing a chloride determination using what is called the Fajans method. I prefer the Mohr method myself, where sodium dichromate is the indicator instead of dichlorofluorescein. Either way, you titrate with standard silver nitrate solution which reacts with the chloride in the sample to precipitate silver chloride. After all of the chloride in the sample is consumed, the excess silver ions are free to react with the indicator which signals the endpoint.

Jon Barrows
Jon Barrows, MSF, EHSSC
GOAD Company
supporting advertiser
Independence, Missouri
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October 4, 2010

Thanks for the response guys. I might try the sodium dichromate method some day, but since I've been away for a while I would like to do the titration using the method I am used too.

Jason D
- Grand Rapids, Michigan



October 9, 2010

Whether using fluorescein or chromate, it is important to control the pH of the sample as you are titrating, as both indicators are sensitive to pH. Add approximately 0.5 gram of calcium carbonate to the diluted sample, swirl, then add the indicator of choice and titrate..

Mike Burnson
- Chicago, Illinois, USA


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