Determination of the concentration of gold solution

"Gold Plating Technology"
by Reid & Goldie
-- hard to find & expensive; if you see a copy cheap, act fast!


on Amazon or eBay
or AbeBooks
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A. Hi Maria. Reid & Goldie has a 25-page chapter on Analysis, including gravimetric methods. Unfortunately, I can't tell you where you can source an affordable copy of this increasingly hard to find book :-(
But according to worldcat.org, the University of Birmingham, which they claim is 18 miles from Coventry, has a copy :-)

Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Maria
Nearer to you then Birmingham is PMD Chemicals, a major supplier of plating solutions who have their main office in Coventry.
Gravimetric gold is not quite as simple as the books suggest and it helps to see a demo. If you contact PMD and ask nicely you might be invited to the lab or even get a visit from their technical rep.

A. Hi,
There are approx. 8 to 9 methods of gold assay: volumetic, gravimetric, fire assay, by potassium iodide, XRF, and so many.
I suggest you put an ash-less filter paper in plating bath, burn it; you will get the residue, purify it again, and check the assay.

A. Most people would use atomic absorption spectroscopy ⇦ on eBay or Amazon [affil link] .

XRF Coating Thickness Analyzer

on Amazon or eBay
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A. Corrine,
If you don't have access to an AA, there are a couple of other methods you could try. If your company uses an x-ray fluorescence spectroscope to measure thicknesses, you can install software in it which will quantitatively analyze gold ion in plating baths. It's a fairly simple procedure, but standardizing is tedious. Also, if you don't calibrate it on a regular basis, your results will be about as accurate as a scud missile.
Gravimetric analysis is another option. By reacting a 5 or 10 mL sample of your solution with sulfuric and nitric acids, with heat, followed by complete reduction using hydrogen peroxide, you can extract gold metal which may be weighed on an analytical balance. That procedure is widely known and available.
Best bet? James was right. Atomic Absorption.

A. By whatever means that is recommended by the mfgr. of the solution or the salts.

Barring that, get an analysis book and find a method that will work for your particular alloy (hopefully in your budget also). The best methods are expensive.

A. I used to do this: I had a piece of platinum clad titanium gauze, about 15 cm2. I'd take a bath sample, add a gram of sodium cyanide, dilute to a suitable volume, and make it the cathode in a little plating cell I made out of a cut down plastic bottle. I used a little piece of 12 mm stainless rod as the anode. Apply current for about 40 minutes, with stirring.

Weigh before and after.

A. Dilute 1.00 ml solution to 100 ml with distilled water.

Digest 10.00 ml of this solution (in a fume hood) with 5 ml aqua regia. Hydrogen cyanide will be evolved. Warm gently until all solids dissolve.

Transfer quantitatively to a 100 ml volumetric flask [100 mL flasks on eBay or Amazon [affil link] and dilute to volume. If your bath Au concentration was 5 g/l you'll get 5.00 mg/l in your sample prep. This ought to be within the linear working range for Au. You may have to dilute the sample prep. a little more.

Evaluate concentration by comparing to s standard curve made with distilled water and at least three Au standards.