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Test for citric acid in nickel phosphorous plating bath

 

I am looking for a test method to determine citric acid in nickel phosphorous plating baths. What about UV/VIS? What would be the right wavelength?

Terri Christison
- Fremont, California

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I have no experience with this problem. To the best of my knowledge, citric is only lost through dragout.

citric acid has no conjugated C=C/C=O bonds. I doubt that its extinction coefficient is high enough to let you see it with much accuracy through the noise in UV.

Off the top of my head, you might try:

1) Finding a transition metal ion that forms a highly absorbent citrate complex in the visible range, and making a series of standards to read in the visible range. Likely candidates that come to mind would be cobalt or manganese. You would not, of course, see the citric that is already complexed to the Ni in the bath. This might be gotten around by determining the total nickel, and matching this in the blank solution used to make up the citric/transition metal ion standards. The calibration curve would likely be nonlinear, so you'd need at least 5 standards.

2) To a measured aliquot of your Ni/P bath, add 30% hydrogen peroxide (I am assuming that this is an electroless Ni bath, and that hypophosphite is present) until a drop of the solution fails to decolorize a drop of 0.01 N iodine solution. Boil for a few minutes to decompose excess peroxide.

Then, add a known excess of ceric ammonium sulphate solution, along with enough sulfuric acid to reduce the pH to less than 1. Boil this for about ten minutes. Let cool, add ferroin indicator, then back titrate with ferrous ammonium sulphate solution to a red endpoint. By calculation, it will be possible to determine the number of equivalents of ceric consumed in the oxidation of the citric. It may be possible to calculate the titrimetric equivalent of the citric, or you might have to do a run on a known citric standard.

As I say, these are just rough ideas. You'd need to do a fair amount of experimenting to see whether either could become a viable method.

Check Meites Handbook of Analytical Chemistry ⇦[this on Amazon affil links]. It has numerous procedures for determining all kinds of substances. It's helped me many a time.

Hope this is of some assistance.

Dave Wichern
Consultant - The Bronx, New York

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Oops. I got the endpoint mixed up. In the backtitration with ferrous ammonium sulphate solution, it starts out red. The endpoint is indicated by the disappearance of the red color, and the solution turning pale blue. Sorry, I hope I didn't confuse you.

Dave Wichern
Consultant - The Bronx, New York

I need to do assay of citric acid by using UV/VIs.but I don't know what wavelength should I use?

Fayer Lau
Universiti malaya - Malaysia
2007