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Cyanide Brass/Copper plating solution analysis

October 6, 2021

Q. Hello! I am employed by a small plating company and just recently our lab has been having trouble analyzing our brass and copper strike plating baths for free cyanide. Our titration method uses the bath sample, DI water and 10% KI titrated with 0.1 N silver nitrate to a pale yellow endpoint. Instead of the pale yellow, our solution is turning a gray-black. Initially we thought that we were experiencing high sulfides thus causing the precipitation of silver sulfide. Lead acetate was added to try to remove the supposed silver sulfide with no success. Does anyone have any other suggestions as to what could be causing this method interference? Funny thing is that we are plating just fine. Thank you in advance for your help.

Rebecca Batty
- Peru, Illinois

October 11, 2021

A. Hello Rebecca. In your case, it looks like "pale yellow" should not be the endpoint. The endpoint is turbidity. You want to stop at the earliest sign that the turbidity is not disappearing because permanent turbidity is the indication that you have passed the equivalence point. All that is needed is a bit of patience in those last few drops of silver nitrate. If you think you may have gone too far, it is always a good idea to repeat the titration and were more careful the second time.

The method I used for free sodium cyanide in a copper strike bath is a variation from published methods in that I increased the sample size in order to get a more accurate result for free NaCN range of the bath that I was using (~6g/L).

a. Pipette 25.0 mL of bath sample into a 250 mL Erlenmeyer flask.
b. Add about 50 mL deionized water and about 5 mL of 20% potassium iodide.
c. Titrate with 0.100 N silver nitrate to a faint permanent turbidity.
d. Free Sodium Cyanide g/L = 0.392 x mL of 0.100 N silver nitrate.

Jon Barrows
Jon Barrows, MSF, EHSSC
GOAD Company
supporting advertiser
Independence, Missouri

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Q. I have problem with an analysis. Can anybody help me with how to test Rochelle salt in Copper plating solution?


Benigna Skorobogatiene
electrical components mfgr. - San Jose, California

(to provide context, hopefully helping readers more quickly understand the Q&A's)

The "Metal Finishing Guidebook" was an annual publication included with a subscription to Metal Finishing magazine. Metal Finishing closed in 2013, so the Guidebook is not published anymore..

A. The Metal Finishing Guidebook and Directory has a method. The subscription is worth the money for the Guidebook alone!

The basic method is MFG, comments are mine.

1. 5 ml sample (into Erlenmeyer flask)
2. Add 25 ml 20% sulfuric acid (fume hood!)
3. Filter the precipitate. Wash the flask and filter paper twice each with DI water. Discard the precipitate (contains copper cyanide!)
4. Collect all the filtrate and boil 5 minutes (fume hood!)
5. Titrate solution with 0.1 N potassium permanganate to pink endpoint (this will fade, you need to get it to hold for 10-20 seconds)

Calculate: oz/gal KNaC4H4O6.4H2O = ml x 1.25 X N

Please respond if you notice any errors!

bill vins
Bill Vins
microwave & cable assemblies - Mesa (what a place-a), Arizona


A. Pipette 5 ml Copper cyanide solution into a 250 ml beaker. In a hood, add 10 ml DI H2O and 5 ml HCl. Boil to destroy CN, but not to dryness. Cool, then add 2g Zn dust and allow to react for 30 minutes. Filter into a 250 ml flask and wash the paper. Add 1 g MgSO4, 10 ml 25% H2SO4, 50 ml DI water and exactly 50 ml of KMnO4. Heat to 89-90 °C (do not boil) for about 30 minutes. Cool and add 10 ml 10% KI and titrate with .1M sodium thiosulfate and record volume used as V.

g/l Rochelle salt=(50-V) x 0.938

James Totter
James Totter, CEF
- Tallahassee, Florida


A. This is a fairly straightforward analysis. Take 5 mL of sample by pipet and transfer to a 100 mL Erlenmeyer flask. Add 25 mL 25% Sulfuric Acid to the flask. WARNING: this will evolve Hydrogen Cyanide! Perform in a fume hood. Filter. Wash the flask and filter paper twice with DI water. Boil the collected filtrate for 5 minutes. Allow to cool. Titrate with 0.1N KMnO4 to a pink endpoint.

Calculate Rochelle Salt Conc. (g/L) = mL used x 0.9375

Best of Luck,

Ira Donovan, M.S.F.
Kansas City, Missouri

"The Chemical Analysis of Electroplating Solutions"
from Abe Books

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October 31, 2011

A. Another method that does not need filtering is as follows:
Take 5 mls of plating solution into a flask.
Put in a fume cupboard, add 10 mls of H2SO4, Hydrogen Cyanide gas will go up the fume cupboard. Put the flask on a hot plate and heat until white SO2 fumes appear after the water has all boiled off. Remove from the hot plate, add 100 mls of water. Then add conc. ammonia until a deep blue colour just appears and remains. Add a few drops of 1-(2-Pyridylazo)-2-Naphthol (PAN) as indicator, then titrate to a green end point with 0.1 M EDTA. The colour may go back to purple a couple of times before you get the green end point to remain with addition of further EDTA.

Cu g/l = Titre X 3.169.

Mark Lees
- Isle of Man Great Britain

Can't see color change in titrating for Copper Cyanide


Q. I am having problems seeing a color change while titrating for Copper Cyanide in a Copper Plating bath, here is the method I am using:
2 ml sample, 100 mls H2O, 15 mls Concentrated Nitric Acid, heat to Blue color, add concentrated ammonium Hydroxide to deep blue and then acetic acid to light blue, add 5 g KI, titrate with 0.1N Sodium Thiosulfate to pale yellow, add Starch indicator and continue titrating to a clear endpoint.

My problem is that I am having a hard time seeing the original color change to blue after heating, if anyone can offer any advice or a better method, please help.

Tony Schmaltz
- Kent, Washington


A. Your method requires modification. It is necessary to destroy the cyanide first but then you must get rid of the nitric acid as it is an oxidant and will effect the thiosulphate endpoint. It is usual to add sulphuric acid and nitric acid and then boil until you see the white fumes of sulphuric acid when all the nitric has been also boiled away. This MUST all be done in a fume cupboard. Also fluoride needs to be added at this stage to complex any iron contamination If you don't have a fume hood find a method using EDTA and PAN indicator where the cyanide is destroyed with hydrogen peroxide.

Geoffrey Whitelaw
Geoffrey Whitelaw
- Port Melbourne, Australia


"Analysis of Electroplating & Related Solutions"
by Langford & Parker
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A. We use a similar method, which is very accurate and repeatable. Probably the differences lie in the details. Here is our method:
a) Pipette 10 ml sample into a 250 ml Erlenmeyer.
b) Add 5 ml Sulfuric conc. and 1 ml Nitric conc. Acid while shaking under a hood. WARNING! dangerous HCN gas is evolved.
c) Boil until dense, white sulphur trioxide fumes are evolved, to eliminate all nitric acid.
d) Cool and add 100 ml deionized water.
e) Add Ammonium Hydroxide conc. until the solution is colored dark blue and a definite ammonia odor can be noted.
f) Boil for 15 minutes or until all excess ammonia has been vaporized.
g) Add 2 gr Ammonium Bifluoride and 10 ml Acetic Acid (5N) and at this point the solution turns to light blue.
h) After cooling at room temp. add 25 ml Potassium Iodide (20%) and shake.
i) Titrate with 0.1N Sodium Thiosulfate until the brown color of the solution begins to turn yellow.
j) Add 2 ml starch indicator solution, 2 g Ammonium Thiocyanate and continue titration until the blue color disappears and does not return for about 1 minute.
k) Let A ml be the volume of Sodium Thiosulfate consumed.

CALCULATION. Copper Cyanide, g/l= A x N (of Sodium Thiocyanate) x 8.94

Angela Nikolaou
aerospace industry - Tanagra, Greece

Copper plating solution analysis, Potassium Cyanide


Q. I have a problem with an analysis. Can anybody help me with how to test Potassium Cyanide in Copper plating solution?

Avel Berroya
- Harbor City, California


A. Avel Berroya, you can have the analysis from metalfinishing.com, then go to chemical analysis of plating solutions or control, analysis and testing.

popat patel
Popatbhai B. Patel
electroplating consultant - Roseville, Michigan


A. That's not hard. Combine 5.0 ml of plating bath with about 100 ml of distilled water in a flask. Add about a gram of potassium iodide, and swirl the flask until it is dissolved. Then, titrate the mixture with 0.1 N silver nitrate solution. The endpoint is a persistent yellowish white cloudiness. Then, multiply the mls silver nitrate used by 0.347 for "free" potassium cyanide, in ounces per gallon.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

EDTA and PAN indicator method


Q. I'm working in a electroplating company as Lab assistant. I had to analysis the copper cyanide solution, but I need to use the method which use the EDTA and PAN indicator. Please give me the information?

Png Aik Fong
electroplating - Singapore


A. Pipette 2 ml sample
Add approx. 1 g ammonium persulphate Warm to decompose CN
Add 10 ml of ammonia and approx. 100 ml DI water
Add PAN indicator and titrate with 0.1M EDTA.

1ml EDTA = 0.00637g Cu

Geoffrey Whitelaw
Geoffrey Whitelaw
- Port Melbourne, Australia

March 4, 2017

A. Mr. Whitelaw offers sound advice, as usual. The only thing I'd do different is to use H2O2 for prelim. CN destruct.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

Ammonia and Muroxide indicator method

July 18, 2008

Q. I'm working in a electroplating company as Lab assistant. I had to analysis the copper cyanide solution, but I need to use the method which use the Ammonia and Muroxide indicator. Please give me the information?

marwa nour eldin ibrahim
Cairo, Egypt

April 2, 2011

A. 10ml sample solution dilute to 100 ml
get 5 ml sample
add 50 ml water
add 10 ml ammonium hydroxide
add 2-3 ml of muroxide solution
endpoint purple

6.35 x F x V

- Cebu, philippines

How to correct 3% to 4% error


Q. Dear Sir,

I'm working in a Pharmaceutical company (R&D) as Lab assistant. I had to analyze copper cyanide, I am not having the correct method of analysis of the same. My results are varying about 3 to 4 %. Please give me correct method with specification. Which precautions do I have take at the time of analysis? I will very thankful to you.

Thanking you,

Babasaheb E. Dalvi
Lab assistant - Kharghar, Navi Mumbai, Maharashtra, India

Hi Babasaheb. We appended your question to a thread which may answer it, but please get back to us with any further questions.


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

April 2, 2009

Q. How to analyse hydroxide in cyanide copper plating onto zinc?

Olga Tubin
Lab technician - Canada

January 31, 2012

Q. Hello folks,

My name is Bruno Pires and I am from Brazil. I work in a aeronautic company that supplies non destructive tests, chemical treatments and painting.

We are developing a small line for copper plating. I found some potentiometric bath analysis method, but we don't have this equipment.

I would like to know if there is another kind of bath analysis instead of potentiometric method, for example by titration and color change.

Bath composition:
Caustic Soda [affil link] : 13,7 g/l
Sodium Cyanide: 4,7 g/l
Copper Cyanide: 37 g/l
Rochelle Salt: 49,8 g/l
Temperature: 50 - 60 °C

Bruno Pires
- Sao Jose dos Campos, Sao Paulo, Brazil

February 3, 2012

A. Hi Bruno,

There are some really useful volumetric methods in this publication by Charles Rosenstein and Stanley Hirsch. You will find most of what you are looking for:

Emily Gardiner
Chemist - Poole, Dorset

May 28, 2013

I have two questions:

Q1. Can someone help clarify the solution analysis procedure for free potassium cyanide in a copper cyanide bath? We have two different sources with different analysis and we are unsure which to use. Both sources have the same procedure: 10 mL sample, add 100 mL DI water, and 5 mL of 10% potassium iodide. Titrate with 0.1N Silver iodide until a faint yellow precipitate.

Source 1: mL 0.1N Silver nitrate x N silver nitrate x .173 = oz/gal free KCN
Source 2: mL 0.1N Silver nitrate x .173 = oz/gal free KCN

The differences are a factor of 10 (the normality of the silver nitrate). Can someone please help clarify which to use?

Q2. For a cyanide copper bath that uses KCN, CuCN, KOH, and brighteners, what is the difference in measuring the "free cyanide" or the "free potassium cyanide"?

Thank you in advance

Karen Gibbs
- Mount Prospect, Illinois, USA

June 2, 2013

A1. Hi Karen. On the thread we appended your inquiry to, Dave Wichern has told us that Source 2 is the correct one. Further, the Source 1 formula sounds like a very awkward way of expressing the situation, so I'd guess it's just a typo or transcription error; my bet is they meant to say multiply the mL of silver nitrate titrant times its normality times .173 -- which would make it agree with Source 2 and with Dave.

A2. I don't think there is any difference between "free cyanide" and "free potassium cyanide". Some cyanide plating baths are based on sodium cyanide rather than potassium cyanide, in which case I don't think there would be any difference between "free cyanide" and "free sodium cyanide". But I'm no chemist so corrections are certainly welcome.


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

July 25, 2013

Q. Hi, I've tried Mr. Totter's Rochelle salt analysis procedure. It's a better titration than titrating with KMnO4. But actually there is something wrong with my Rochelle amounts. I've tried with 0.1N KMnO4 addition. It shows up to be 3 times larger than I've expected. Can you help me about how I can adjust the normality of my KMnO4 solution?


Nilufer Ulgudur
- Ankara, Turkey

March 2, 2017

Q1. Hi sir,

please help me to know criteria to decide if copper cyanide is good or know to use it in copper cyanide bath.

I had copper cyanide containing 55% copper metal. It is acceptable or not?

Q2. My other question is about Role of Hydroxyl group in copper & brass Bath and How to determine it?

asmaa El-sayed
Chemical Engineer - Alexandria, egypt

March 15, 2017

A. For NaOH you titrate to a sulfo orange endpoint with 0.1 N HCl. Look up the factor.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

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pdf is currently available from academia.edu

March 2017

A. Hi Asmaa. Copper cyanide, CuCN, is 71% copper. But a plater might buy soluble K2Cu(CN)3 or Na2Cu(CN)3, thus about 34% or about 29% copper. Plating shops generally buy process chemicals from trusted sources, they don't simply find chemicals somewhere and then test for every possible contaminant which might be problematical -- they'd have no time for plating :-)

Copper cyanide plating is the subject of 20-page chapters in many plating text books, so it's hard to say how to use it in a paragraph or two... maybe you can be a bit more specific with your question? But in the meanwhile, the Metal Finishing Guidebook has a pretty good explanation of the subjects of your inquiry. Good luck.


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

March 30, 2017

thumbs up sign Hi.

Thanks, valuable book.

Q. Mr. Dave, can I use methyl orange instead of sulfo-orange indicator

Asmaa el-sayeda [returning]
Chemical Engineer - Alexandria, egypt

April 8, 2018

Q. Can anyone tell me the volumetric procedure to calculate sodium potassium tartrate in copper cyanide bath? Is there any volumetric procedure to calculate total sodium cyanide in copper cyanide bath?

General purpose tank used for cooper plating zinc based die casting should be like:
Copper cyanide: 30 grams per lite
Total cyanide: 48 grams per litre
Free cyanide: 15 grams per litre
Rochelle salt: 30 grams per litre
sodium carbonate / washing soda [affil link]: 15 grams ler litre
Sodium hydroxide: 5 grams per litre

Also tell me the procedure to calculate sodium hydroxide and sodium carbonate in the bath.

I am facing blistering problem after my object is subjected to heat and polishing or it is taken to nickel bath.
Is this due to low cyanide or high cyanide in my bath..
What is the perfect ratio for free cyanide and copper cyanide in copper cyanide bath.

I have checked my pre plating procedure several times
It is like:
Tri chloroethylene cleaning, ultrasonic cleaning, anodic cleaning, cathodic strike cleaning, Sulphuric acid dip in 3 percent solution for 10 secs and 10 sec dip in hydrofluoric acid and after that cyanide plating.

Nikhil sharma
SMC - Jalandhar, Punjab (India)

Chloride in Copper Cyanide Plating Bath

November 19, 2018

Q. Hi, my name is Lamberto and I work at a galvanic for the aeronautical sector. I am afraid of having chloride contamination and I would like to determine its concentration in the cyanide copper bath. Do you have a method to suggest? Can you tell me an acceptable maximum limit?
Thank you.

Lamberto Carlini
- Foligno, Umbria, Italia

December 19, 2018

A. Hi Lamberto. Google the Mohr method, or Fajans method. Each are relatively simple to perform, I typically use them for our acid chloride zinc bath. Do a bit of digging and ensure that it will function in an alkaline environment but I believe it should serve your purpose. As always when dealing with cyanide, take the necessary precautions; I am sure someone more knowledgeable on the subject may be able to offer better advice, but this should give you a place to start.

- Jordan

Jordan Egnatoff
- Huntington, West Virginia, USA

December 20, 2018

thumbs up sign Thanks for the directions, for now I tried with a colorimetric method that gave good results; I will try to compare them with those suggested.
Thank you

Lamberto Carlini [returning]
- Foligno, Umbria, Italia

December 20, 2018

A. Thinking about this further, those methods may work, but the silver nitrate is going to bind with the cyanide in solution as well. Not sure which would be preferential, I'd guess the cyanide, but if you did try it you could start measuring the chloride content once the precipitate appeared. Glad you got some results though, if you don't mind me asking, where do you think your source of chloride may have come from? Did it seem to cause any adverse affects on the plate?

Jordan Egnatoff
- Huntington, West Virginia, USA

December 21, 2018

Surely I will have to eliminate cyanides by acidifying the sample to avoid precipitation, I'm used to control the Rochelle. The chloride source is definitely the previous pickling, there are three rinses before going into copper, but sometimes the pieces are complex and can drag liquids, sometimes the guys in production are too fast ... small pinholes that can compromise subsequent heat treatments; however, increasing the time and flow of rinsing water the problem has disappeared.
Thanks again for the availability.

Lamberto Carlini [returning]
- Foligno, Umbria, Italia

June 24, 2020

← Posters: please describe Your actual situation.

Q. Hello friends,
What is the procedure to test carbonate levels in Rochelle based cyanide copper bath?

Arpit jain
- New Delhi , India

July 2020

thumbs up sign Hi Arpit. We appended your question to a thread where it has been discussed for 19 years now :-)

If the answers are insufficient for your needs, please expound with the details of your situation. Thanks!

Luck & Regards,

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

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