46008

Badly need guidance on Albaloy plating bath analysis [Massachusetts] 

August 2, 2007

Hi, my name is jerry and I'm a plater for a electronics company. My question is about the albaloy bath I use. Can I determine the copper, tin, and zinc concentration by using titration methods? My vendor tells me the only way is by AAS. I am currently using an x-ray machine but, this method seems to be inaccurate and inconsistent. If I can use titration methods PLEASE, can you tell me the procedure for each metal?

thank you,

Jerry Hannibal
lead person - Beverly, Massachusetts, USA

Hi Jerry

You should be able to use your x-ray machine for all three of these metals - especially if you are trying to measure them at g/L or % types of levels. I would use the method of standard additions and it should work.

Terry Tomt
- Auburn, WA

A Google search on "Albaloy" tells me that it is a cyanide based alkaline formulation, also known as "white bronze."

Zinc can be determined as in a brass solution: titration with EDTA after blending with a pH 10 NH3/NH4Cl buffer, and a formaldehyde addition. The indicator used is eriochrome black 'T'; the endpoint transition is red to blue.

Copper, plus zinc, will come up in an EDTA titration also. The cyanide is destroyed, via the addition of hydrogen peroxide, and subsequent addition of HNO3 and H2SO4 (caution! cyanide gas released!)and heating to white fumes. Water is added after cooling, aqueous ammonia added just to a blue color, PAN indicator solution added, and the mixture titrated at about 140 F with EDTA to a light green endpoint. A little arithmetic, subtracting the Zn number, yields the Cu number.

Tin can be determined as in a bronze solution. A suitably sized sample is combined with about 40 ml of conc HCl (caution! cyanide gas released!) and heated until gas evolution ceases. About 60 ml of water and 2 - 3 g iron powder are added, and the mixture boiled until the iron dissolves. About a gram of NaHCO3 is added, the mixture covered loosely, and allowed to cool. A bit of starch indicator is added, and the mixture titrated to a blue endpoint with iodine solution.

If I was mistaken about this being a cyanide formulation, and the complexant is some kind of organic chelator, the zinc determination has to be finagled - a good sharp acid digestion, followed by ammonia addition to pH 10, will get rid of the chelator and allow titration in the usual fashion.

Dave Wichern - Bronx, NY, USA

Minor emendation: If you do the acid digestion for Zn in a non-cyanide formulation (if that is what you have) after the post digestion elevation of the pH, you need to add 300-400 mg of sodium cyanide to mask the copper. When you add the formaldehyde, the zinc will be unmasked, but not the copper.

Dave Wichern
- Bronx, NY, USA