The authoritative public forum
  for Metal Finishing since 1989
-----

Taking a representative plating bath sample

Is there a difference between samples taken from a plating bath without barrel and with a (working) barrel inside?

If yes, what is the right way to take samples for concentration analysis?

Frans Michiels
Plating shop - Quer´taro, Mexico
2006

---

Hi Frans,
I was trained years ago to draw my samples without work in the tank. If you draw a sample while plating and you have soluble anodes, your sample will contain a slightly higher metal concentration then a sample drawn from an idle bath. During electrolysis there is constant anode erosion, so in effect you are sampling the ions before they have a chance to be deposited on the cathode. The higher the current density the more erroneous your sample will be. The most accurate method I have found is to sample when the bath is heated to temp, filter pump running, and tank idle. Good Luck!

Mark Baker
process engineer - Malone, New York
2006

---

Then, too, taking a sample with work in the tank may be a safety violation per OSHA (less likely) or per a company's internal safety standards (more likely).

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

---

Yes there is a difference. To properly take a sample a sampling tube (glass or appropriate plastic) is used to take a series of small samples from different areas and depths of the tank, placed together in one container this forms a representative sample which will mitigate the problems of varying concentrations near filter inlets, outputs, agitation areas, etc.
Please note that the tank should be at or near operating temperature and well mixed before taking any sample to insure that all salts are dissolved.

Gene Packman
process supplier - Great Neck, New York
2006

---

I have to agree with Mr. Packman on this one, we always take our samples, with the baths up to temperature,air on if applicable, and the filter pumps running. This way just as Gene has said you will stir up any undisolved salts from the bottom of the tank.

Best Regards

Brian C. Gaylets
- Scranton Pennsylvania, U.S.A
2006

---

2006

While I agree with the advice on sampling there is one critical thing not mentioned.
The solution level should be at a standard level.
So often the level will be down when a sample is taken due to evaporation, and suddenly the concentration has risen.
Say 2 inches down in a 36 inch deep tank is over 5% and makes the difference of 16g/l in a 300g/l nickel tank.
So if you sample when the level is down make a note and specify that the results are probably x% high due to this factor.

Geoffrey Whitelaw
- Port Melbourne, Australia