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Determining ammonia Concentration in a Brass Plating Bath

Q. Is there any way of testing the ammonia [on eBay or Amazon affil links] concentration of a brass plating bath?

Jason Deible
- Grand Rapids, Michigan

A. Maybe ISE would work.

James Totter
James Totter, CEF
- Tallahassee, Florida

Analysis for ammonium in brass plating baths

Q. Hello, Could you please advise on analysis of ammonium in brass plating bath? I only found one application bulletin which says with Kjeldahl method. Is there another way to find out the concentration of ammonium in my solution so as to keep stable the ratio of Cu:Zn 70:30 in my deposit?
Thank you so much for your help

MATINA Tsolaki
November 2, 2015

A. Mr. Trotter is right on, as usual.

Do ISE via an ammonia selective electrode. It will be necessary to use the method of additions, if you want to avoid the distillation. The math is kind of complicated but it's doable.

Or just go ahead and do the darn distillation. It is not so hard and you can then get to your answer via simple acid base titration.

dave wichern
Dave Wichern
Consultant - The Bronx, New York
November 6, 2015

A. Hi Matina.
I run a 400 liter brass plating bath using barrel to plate chain components. I use brass salts from chemical suppliers. ammonia is added daily about 100 ml per operation day. On longer shutdown...200 ml. I do not titrate for ammonia content. I have no problems keeping the Cu/zinc deposition ratio. Hope this helps

SK Cheah
- Penang Malaysia
December 1, 2015

Q. Hello, is there anyone that has done Kjeldahl analysis to determine ammonium in brass plating bath? I have found an analysis that says 5 ml sample with 4 mo FeSO4 and 15 ml NaOH 20% to the distillation flask and begin distillation immediately. The ammonia is distilled in a solution of H3BO3 2% and then titration with HCl 0.1M.

One question is: do we put all reagents together from the beginning? Shouldn't we first do the digestion with sample and FeSO4? And then distillation with NaOH?
If someone knows an analysis please advise.
Thank you,

MATINA TSOLAKI [returning]
November 26, 2015

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