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Using titration to find nickel concentration in Zn/Ni electrolyte

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Q. I was wondering if anyone has experience with zinc-nickel plating and knows of any titration methods for determining zinc and nickel metal content. The bath we use is an Enthone product. It is made up of ammonium, nickel and zinc chloride. Aside from not able to use the testing procedure supplied from Enthone with any accuracy the other problem with the bath is the zinc metal climbs much faster than the nickel. Can nickel only be raised by adding nickel chloride, or is there another way to raise nickel without overloading the chlorides.

Kevin G [last name deleted for privacy by Editor]
- Trenton, Ontario, Canada


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Q. Hi everyone,

Does anyone know how to make nickel analysis in an alkaline Ni-Zn plating bath without using atomic absorption (AA) method?

We are currently working on a project involving Zn-Ni plating. However, plating solution manufacturer wrote in their technical document that only AA can be used to analyze the nickel content of their bath. The big problem is that we don't have any AA (shame on us!). I was thinking about using UV/VIS spectrophotometry, but I don't know if there is possible interferences.

Anyone can help me?

Regards,

Daniel Picard
research council - Boucherville, Qc, Canada


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A. To find the Nickel concentration in an alkaline Zn-Ni bath by UV-Vis, you can use nioxime (1,2-cycloheanedione dioxime). A typical procedure for about 2 g/L nickel would be to acidify an aliquot to break the nickel complex. Add a complexing agent for interfering impurities, e.g. Fe, such as ammonium citrate. Add a pH 5.5 acetate buffer to control the pH. Add a supporting dispersant of 50 g/L Gum Arabic (about 1:99 volumes). Then add the nioxime reagent, prepared at 5 g/L in 9:1 aqueous ethanol, at 2 mL per 100 ml for a maximum 4 mg/L nickel solution. The red suspension absorbs at 550 nm. A calibration curve should be prepared.

Billie J. Page
- Cleveland Heights, Ohio


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A. Dear Daniel,

There may be a couple of alternatives to the AA for your application. The first method is an ion selective electrode. This technology has been used in the metal finishing industry as a cost alternative to more expensive and accurate equipment. Here is the drawback, these electrodes have many interferences and in some cases lack the necessary accuracy required for analysis. The second method is to use your aforementioned UV/Vis. There are a few different methods, of which the most reliable that I have found is the use of Dimethyl Glyoxime. This method uses forms a complex which is easily measured at 445 nm. The last method is a complexometric titration using automated titration equipment. The new advances in the titration equipment industry can allow the nickel to be determined separately from the zinc. It is preferred that you contact appropriate manufacturers of equipment to determine the proper fit to your need.

Best of luck.

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


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A. Dear Daniel,

I currently have a plating operation where we are plating zinc-nickel, and have used several methods for measuring zinc and nickel solution concentration. Yes you can measure nickel concentration with spectrophotometry with less than 2% error. The procedure that I use takes forty minutes to perform. A good chemical supplier can provide with this test method. You can also measure both zinc and nickel concentration using a XRF analysis or X-ray thickness tester with a solution cup. I found that this method has an error about 8%; however, the analysis only takes 4 minutes to perform. In my shop, we used the XRF method 99.9% of the time because it is fast to do, baths can be checked more often, and we find the error acceptable.

Karl Weyermann
- Lebanon, Kentucky


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thumbsup2Thanks a lot everyone for your answers. It's greatly appreciated.

Daniel Picard
research council - Longueuil, Qc, Canada


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Q. Dear Karl Weyermann,

Can you please tell me more about using XRF/X-Ray thickness tester to determine Zn and Ni concentration in an alkaline Zn-Ni bath?

Thanks.

Prabhu Ganesan
University of South Carolina - South Carolina



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Q. Hi,
I work with Zn-Ni solutions made by mixing the sulfate salts of these metals in water. We use this solution for coating and after a few coating trials we don't know the amount of Zn and Ni left in the solution. Can we do simple titration to determine the amount of Zn and Ni? What is the method and what are the chemicals needed?

P George
Engineer - USA


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A. Zinc: Dilute a 10ml bath sample to 100ml in a volumetric and pipette a 10ml aliquot of the dilution into a 250 ml flask and add 10 ml 10%NaCN solution. Add 100 ml DI H2O and 10 ml of pH 10 buffer (70 g NH4Cl, 570 ml 88 Be NH3, balance DI to 1000 ml in a volumetric). Add 10 ml 10%HCHO and .1g erichrome black T indicator. Titrate immediately with .1M EDTA to a blue endpoint. g/l Zn=(ml EDTA)*6.54

Nickel: Make the following:
Solution A: 30g sodium pyrophosphate, 50 g NH4Cl, 2g KI to 1000ml total with DI.
Solution B: 25.5g NaCN, 1.7g AgNO3 to 1000ml total volume in a volumetric flask with DI (transfer this to a dark glass container and store in the dark).

Pipette 5ml bath into a 250ml flask and add 50ml solution A. Add 88 Be NH3 until the pH is >8.0. Titrate with solution B until the turbidity just disappears. g/l Ni=(ml solution B)*1.5

totter James Totter, CEF
- Tallahassee, Florida


March 3, 2009

Q. My company has recently added 2 alkaline Zinc/Nickel electroplating bath. However, the photometer that we use to find Nickel concentration is unable to accurately find the nickel concentration due to interference in the electrolyte. I want to ask if it is possible to use do chromatography and then use titration to find the concentration. If yes, how can I do it? Thanks in advance!

Yong Quan Lam
plating employee - Singapore


First of two simultaneous responses -- March 6, 2009

A. Since you say photometer rather than spectrophotometer, I think that you do not have an adequate piece of equipment. If it is using "color" slides to determine frequency, it definitely is not adequate. You need a precise control of the light frequency to do an analyzes for nickel in a solution that has other items that react at a broad frequency.

James Watts
- Navarre, Florida


Second of two simultaneous responses -- March 7, 2009

A. I would do two EDTA titrations - one with aqueous NH3 added, using murexide indicator. This will give you the total metal.

Then, a second, with pH 10 NH3/NH4Cl buffer, Eriochrome T indicator, and 0.3 - 0.5 g potassium or sodium cyanide added. 10 ml of 10% v/v formaldehyde should be added right before starting the titration, which should be carried out as quickly as possible. This will give you the zinc number - the cyanide will mask the nickel.

Nickel can then be determined by simple arithmetic, subtracting one number from the other.

dave wichern Dave Wichern
- The Bronx, New York

March 17, 2009

Q. No disrespect, but I read that cyanide masks the zinc instead of nickel right?

Lam Yong Quan
- Singapore


March 19, 2009

A. No, the cyanide masks the nickel. It forms a complex that is too strong for the formaldehyde to break.

Another idea I had is; dilute to a suitable concentration (10 - 20 ppm Ni) and analyze with the dimethylglyoxime colorimetric method, employing the method of additions. Or, make up Ni standards in a matched matrix, and read directly.

Dave Wichern
- The Bronx, New York

March 23, 2009

Q. I have a few questions. The first test to check the no. of mol of total metals, what concentration of NH3 should I use? Second, won't the excessive cyanide mask the zinc? Won't it affect the reading of Zinc? Lastly can you roughly describe the Colorimetric Determination of Nickel with Dimethylglyoxime.

Thanks a lot!

Lam Yong Quan
- Singapore


March 26, 2009

A. The amount of cyanide I said to use may be excessive - you would have to experiment. As long as there is an excess of formaldehyde the zinc will be unmasked.

Dimethylglyoxime method: Add enough 1:1 HCl to bring the pH of a 10 ml sample to approximately 5; then, add 1.0 ml more. Add roughly 0.3 g ammonium persulfate; shake till dissolved. Add 1.0 ml 10 % sodium citrate solution, shake. Now, add 1.0 ml 1 % dimethylglyoxime solution in alcohol, and immediately add 2.0 ml 1:1 aqua ammonia. Shake well. Wait 10 minutes, then measure the absorption at 420 nm.

Dave Wichern
- The Bronx, New York

April 10, 2009

Q. One last question, what is the concentration of ammonia used? I have a bottle of 25% ammonia, hence I need to know how much I need to dilute it with. Thanks alot!

Lam Yong Quan
- Singapore


April 11, 2009

A. If I recall correctly, standard aqua ammonia, or, "ammonium hydroxide", is 29% by weight.

Go ahead and use what you have, it should do.

Dave Wichern
- The Bronx, New York

April 13, 2009

Q. I am currently doing the titration for both nickel and zinc. I added 10 ml of 25% ammonia and 0.1 g of murexide indicator to the electrolyte and titrated with 0.1 mol of EDTA. However, there is no distinct colour change. The end point and the start point looks pretty similar. Am I doing anything wrong?

Lam Yong Quan
- Singapore


First of three simultaneous responses -- April 14, 2009

A. First; 0.1 g is far too small a sample size. Try 10 ml.

Second; this bath contains powerful complexants, or chelating agents, to keep the Ni in solution at the operating pH of the bath. It may be necessary for you to do a very aggressive acid digestion to eliminate them for the traditional titrimetic methods to work.

I would take 20 ml of plating solution, add 25 ml DI water, 10 ml nitric acid, and 10 ml sulfuric acid. Then, I would heat to white fumes (with adequate ventilation, of course) until a clear green solution was obtained. It might be necessary to add more sulfuric acid, if you see charred products of the complexant oxidation.

Let cool, add water cautiously with lots of mixing. Let cool again, transfer quantitatively to a 200 ml volumetric flask. Make up to volume, and split into two 100 ml aliquots, for the Zn and Zn/Ni titrations, respectively. Each 100 ml will contain 10 ml of sample; make your calculations accordingly.

You will need to neutralize all of the acid you added with aqua ammonia. Make sure to do this before adding any cyanide!

Perhaps, you now begin to see why the plating vendors suggest using AA. :)

Dave Wichern
- The Bronx, New York

Second of three simultaneous responses -- April 14, 2009

Q. To add on to what I say, the starting point was purple which was also the colour of the "end point". My suspicions are either the excessive murexide indicator, the low concentration of nickel ions (they can go as low as 0.5 g/L) or the other chemicals present in the electrolyte that causes interference. However I am not sure. I am currently doing more tests based on these suspected problems.

Lam Yong Quan
- Singapore


Third of three simultaneous responses -- April 15, 2009

A. Far too much indicator. You literally need a few crystals, otherwise the colour change becomes impossible to see. Try about 5 crystals initially. You may need to added two or three more if the colour is not definite enough.

Alternatively mix the indicator with solid sodium chloride (about 1% indicator), then add at about 0.1 g of mixed NaCl/Murexide. Again you may have to play to get the right mix.

Brian Terry
Aerospace - Yeovil, Somerset, UK


April 15, 2009

Q. Well I do realise that this is getting more n more complicated. My boss' refusal to invest in a machine means I have to find it in this way.

Anyway, thanks for the suggestions, I have found an easier way to find Zinc via using xylen orange. Now I need to either find the total amount of metals in it by using Eriochrome Black T or I find the amount of nickel by adding phosphoric acid and ammonia then murexide indicator. I wonder if this will work.

Lam Yong Quan
- Singapore


December 20, 2011

A. The method suggested by Dave Wichern is the best for you. Take 10mL of the solution to be analysed. Add 10mL 25% Ammonia and 0.5g Murexide indicator. If colour is not yellow or dark yellow, add more ammonia. Add 80mL water. Titrate against 0.05M EDTA from yellow to violet. This gives the total metal (Zn + Ni). Next, take another 10mL of the solution. Add 0.5g KCN or NaCN. Add 0.5M buffer of pH 10.5 (NH4OH/ NH4Cl). Shake well. Add now 10mL Formaldehyde (40%). Add 0.5g Eriochrome Black T indicator. Add 70mL water. Titrate against 0.05M EDTA from wine red to blue. This gives zinc. Difference in EDTA volumes give the volume consumed by Nickel. Calculate now nickel. You can have confidence in this method.

1. Murexide and Eriochrome Black T - Prepare 0.5 g in 100 g KNO3 or NaCl
2. If your company uses very strong complexing agents (not stronger than EDTA of course) then the solution upon addition of ammonia will not turn completely yellow. It will remain greenish yellow. If you can smell ammonia strongly that usually will do. Check pH. Should be around 11 - 12.
3. In case your company uses strong complexing agents, reaction with EDTA will be slow and drop-wise addition with 2 - 3 mins time between drops may be necessary.

I think I have covered most of the points.

V.T.Damodaran
- Chennai, Tamilnadu, India

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