45000

Calibration of Titrations? [California] 

May 2, 2007

Hi,
My name is Robin Smith and I am a ceramic engineer, working at plating the end terminals of ceramic capacitors. We plate nickel and tin onto the capacitors. Our medical customer (ie parts go into pacemakers, hearing aids, implantable devices) is asking for more calibration and control. Specifically, they are asking for a calibration for plating titrations of our nickel and tin titrations. How is a titration calibrated?

Any suggestions are greatly appreciated.
Sincerely,

Robin Smith
Capacitor Manufacturer - Valencia, CA

Yeah... that isn't the easiest to answer directly is it?

What I have done here when the question has arisen is to make sure that my supplier (presumably a lab) can show me some traceable or verifiable certificates for my lab chemicas (presumably they have to certify the concentration - that is all I mean).

Then, make a known sample using lab grade chemicals and titrate it a few times to discover how accurate your readings are and to make sure that they are centered on the correct level.

You may have to use more than one operator doing the titrations and do some statistical analysis of the results (look up R&R studies - Repeatability and Reproduceability Studies and the gauge controls that were, in the past, required by QS9000) before your customer is satisfied with your answer, but that is the basic method.

Good luck!

Jim Gorsich Accurate Anodizing Inc. Compton, CA, USA

Hi Robin,
I have heard (but not seen) auto titration dispensing units for various titrants. This does not include determining end point colors, turbidity, etc. You may want to talk to the customer to let them know you don't have this type of equipment. They probably have a QA person that may not understand laboratory apparatus, and methods of titrations. Some equipment in the lab can be calibrated, and some can't. If a flask or graduated cylinder says 100 mls, we trust that is what it is.
If they insist on documentation of titration calculations and bath additions, maybe that would satisfy them. Some customers demand that the standards be supplied by a laboratory supply house, instead of your lab tech or chemist making them up. That can get expensive as you know. Good luck with the customer.

Mark Baker
Process Engineer - Syracuse, NY, USA

There is an ISO specification that many companies are gradually going to. I think that the number is 15020.
Normally, if you are using burettes, you will uses a calibrated balance to weigh a specified percentage of burette dispensed distilled water. A 50 ml burette might have 5 - 10 samples taken. Pipettes are full quantity and in this case, you would pay for class A glassware. DI water is also weighed.
Another kicker is you normally have to do a 2 point calibration of the balance before and after use.

James Watts
- FL

One common method is the known addition, whereby you make a standard addition of the component being measured to the sample after the titration is performed and then further titrate to the new endpoint. For example, when looking to measure % HCl, you would titrate the sample to the endpoint, make a known addition of HCl, then titrate further to the new endpoint. You can then calculate the % recovery of the known addition as a QC indicator of the titration.

Another method is to titrate a known standard concentration of the analyte in question. You can then adjust the calculations of the titration to account for variations in the titrant solution.

James Totter, CEF - Tallahassee, FL

I've been in your situation before and have a few ideas that may be useful. First, have you tried convincing your customer that this process doesn't require calibration? If your glassware is like mine it has a qualification marked on it; mine has TD 20C, meaning it's set To Deliver the marked volume at a temperature of 20C. As long as your pipettes and burettes are not chipped or broken they are designed to maintain their volumes and don't need to be calibrated. The titration method is based on a chemical reaction that hasn't changed in recorded chemical history. Therefore there isn't anything that can fall out of calibration, so the process doesn't require calibration.

Not all customers will be swayed by the above argument. If the customer is adamant about getting calibration data for the titration process then you can go about verifying the calibration of your glassware. At room temperature one milliliter of distilled water weighs 1.00 grams. Fill your burette or pipette with distilled water and discharge a measured amount onto a tared container on a scale (assuming, of course, that the scale has been calibrated). Record the weight. Do this at least 10 times for every piece of glassware. You now have enough data to calculate a standard deviation or percent error or whatever you need to make your customer happy.

If that isn't good enough then you can prepare some plating solutions at known nickel or tin concentrations and titrate those. Once again you should repeat the test at least 10 times and develop whatever statistical data your customer requires. You may need to prove that your chemicals are certified in their concentrations. A certificate of compliance or some other form of written verification from the chemistry supplier should cover that requirement.

Good luck with your customer relations. I hope that was helpful.

Linda Corrie
- Orland Park, IL, USA

A Certificate of Analysis (C of A) for the standard EDTA you use might do for documentation.

Or, you could purchase standard solutions of nickel and tin from a supply house. 10 g/l solutions, (or 1.33 oz/gal) are available for use as ICP standards. Then, you could document how your observed values match up with the true, and generate control charts, if you like.

Or, you could have a known plating solution prepared by some outside vendor, and use that the same way.

The common theme is documentation.

Dave Wichern - Bronx, NY, USA

Robin
A chemist would not have to ask. This is a serious point. If you are processing parts for a critical application like pacemaker circuits, you have to take the control of bath chemistry seriously. Electroplating is a high tech business and chemical control is another. Neither can be picked up from books or the internet. I think you should take advice on bath control from your supplier and/or a competent analytical chemist.
The direct answer to your question is to buy in certified titration standards. No chemist would find it cost effective to standardise his own. It takes time and skill to get accurate results.

Geoff Smith Hampshire, England

Robin,

One good way is to make lab solutions that mimic your process baths as close as possible. But make sure that you know the exact metals concentrations in your lab solutions.

Then titrate these lab solutions and see what your accuracy and reproducibility is. One big benefit of this approach is that it will help account for interferences.

Terry Tomt
- Auburn, WA

To standardise a titration, you begin with known concentrations of solutions that you will titrate against each other. This is fundemental analytical chemistry. All solutions are made up freshly to precisely known concentrations. The simplest one to do is to titrate N/10 sulphuric acid against N/10 sodium hydroxide. The sulphuric acid is the standard and this is used to find teh exact concentration of sodium hydroxide. The problem with sodium hydroxide is that is absorbs carbon dioxide from the air to form sodium carbonate, so the concentration of sodium hydroxide will alter with time. You need to ensure that the solutions you will use for titrating the nickel and tin baths are standardised. Decide which ones are the important ones and then accurately make up known concentrations of these reagents. Compare them with the relevent standard solutions suitable for your analyses.

There is, of course, an alternative and that is to use either AA or ICP analysis. In both cases, start with an accurately known solution that is about 2-3 times the strength of your working (ie analysis) samples. Then accuratey dilute this solution a number of times and use these diluted solutions as your calibration standards of the AA or ICP. You can then put a sample of your plating solution into the AA or ICP and see what adsorption you get and compare it to your calibration graph. In the case of nickel, I suggest you use nickel sulphate as the standard because nickel chloride can have different amounts of water of hydration and this will affect your nickel concentration. Similarly, I would use tin sulphate and not tin chloride. As a general guide I would recommend you use analytical standard chemcials, not GPC.

Trevor Crichton R&D practical scientist - UK

I have just read the contributions to date - none of which would satisfy a chemical process auditor.
Comparing analysis with a standard plating solution is no good - how do you guarantee the accuracy? At best it monitors precision not accuracy.
You cannot use either sulphuric acid or sodium hydroxide to prepare primary standards - both are hygroscopic and NaOH absorbs carbon dioxide. Acids are standardised against sodium carbonate.
Water weighs 1.00g/ml - but only at 4 degrees C. Glassware is certified at 20C (27C in tropical climes)
Suggesting AA, IPC or an autotitrator is like buying a Formula 1 racing car for a learner driver - in the unlikely event of actually getting the thing to work, you just head for disaster that much faster. (Many people seem to suggest IPC but I have yet to see one in regular use and AA can explode if you get the flame conditions wrong!)
To be practical
Get a copy of "Analysis of Electroplating and Related Solutions [link is to book info at Amazon; also avail. from this link at this link at Abebooks]", Langford, Published by Draper.
Get a copy of any analysis sheets from your plating process supplier.
Get your balance calibrated; use the levelling device. (If you buy your titration standards you may not need a balance)
Learn to use a pipette properly - this is important
Buy certified purity chemicals and titration standards
B grade glassware is sufficiently accurate - but it must be marked.
Record; Method of analysis, bath, date, results, calculations,additions to the bath, bath dilutions dumps etc.
Plot a graph of concentration for all constituents and investigate any unexpected fluctuations.
Take a representative sample for analysis; top up the bath to a standard volume and mix well before taking the sample.
OR - you could just send a regular sample to either your supply house or an accredited lab for analysis.

Geoff Smith Hampshire, England