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Analytical technique for confirmation of 49% HF solution

May 6, 2010

Hello,

I thought my question seemed rather simple until I started looking on-line for a suitable answer. I am trying to set up an etchant solution for the removal of Si Oxides. My customer has requested that I confirm the initial concentration of HF to be 49% and I have not been able to find any mention of a suitable analytical technique. We currently do not perform any HF analysis and I have seen posts explaining the use of ferrous sulfate ⇦this on eBay or Amazon [affil links] , Thorium Nitrate and Specific Ion Electrode. What would be the most simple and least expensive method for confirming our solutions start with a 49% HF concentration?

Thanks for you help!

Rich Frits
Engineer - Derby, Connecticut

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Ed. note: the author of the posting surely knows it, but for the benefit of others in this one-room schoolhouse called the internet, 49% HF is one of the most dangerous materials you'll ever work with, diffusing through your skin to dissolve your bones, sometimes anesthesizing the area so you don't know it's happening.

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Ted's note at the bottom of your post is very important. Hopefully, you are starting out with 49% HF rather than diluting 70% with water. You can use small containers of 70% to top up with proper PPE.
An acid base titration is all you need as long as there are no other acids involved. Cheap, accurate, quick and reasonably safe.

James Watts
- Navarre, Florida
May 10, 2010

And I would go even simpler - buy it at 49% certified off the shelf and don't even test it. Just use it.

Terry Tomt
- Auburn, Washington
May 11, 2010

That is great for the initial start up, but as it is used it must be analyzed to maintain it within some preset limits.

James Watts
- Navarre, Florida
May 12, 2010