Summary for boric acid analysis method Discussion
Boric acid analysis method questions in this thread focus on how to measure boric acid in solution, especially for nickel baths and quality-control documentation. Greg Conti first asks for more detail, noting the method depends on the type of solution being tested. Jenn Wright gives a practical titration procedure for nickel baths: take 2 mL of solution, add bromocresol purple, titrate with 0.1N NaOH to blue, then add mannitol to shift the color back and titrate again; she gives the calculation as boric, oz/gal = mL of 0.1N NaOH × 0.412. Dave Wichern says the topic was already covered in another thread. Daniel Montañés explains why mannitol, xylitol, or sorbitol are used: they complex with borate and make the weak acid easier to titrate visually. Denise Frank later asks for QC methods for registering a boric-acid product, but no specific method is provided in the excerpt.
Q. I just want anybody help to analyze boric acid, but I need a single but exact method. I will be appreciated if anybody can help.
Thanks a lot,
Carlos Antonio
– Guatemala
2002
A. Give a little more info. What kind of solution do you need to analyze?
Greg Conti
– Chino Hills, California, USA
2002
A. The method commonly used is as follows: (for Nickel baths) pipette
[pipettes on
eBay or
Amazon [affil link]
2 mls of solution into 250 flask add 2-3 drops bromocresol purple
⇦ on
eBay or
Amazon [affil link]
titrate with a few drops of 0.1N NaOH
⇦ on
eBay or
Amazon [affil link]
until solution turns blue add 5-6 grams solid mannitol, this will turn back to green color titrate with 0.1 N NaOH until blue. boric, oz/gal= mls of 0.1 N NaOH X 0.412
Jenn Wright
– Dayton, Ohio
2002
A. This has been well covered in 15586.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2002
Q. I would like to know the role of manitol or sarbitol in the boric acid analysis
Porchezhiyan Vedapuri
analyst – Cheyyar, Tamilnadu, India
August 28, 2012
A. The mannitol or sorbitol (I have also seen methods where glycerol is added) forms some kind of complex that increases the acidity of the H3BO3. Otherwise, you couldn’t titrate it directly.
Dave Wichern
Consultant – The Bronx, New York
August 29, 2012
A. Dear Mr. Porchezhiyan,
Boric acid reacts with mannitol, xylitol or sorbitol forming a complex with borate, stabilizing the negative charge and increasing the strength of the acid.
This is because boric is a acid so weak that it cannot be measured by visual titration unless the strength is increased somehow.
Hope this can help you solving your issue! Regards,
Daniel Montañés
fasteners manufacturer – Cañuelas, Buenos Aires, Argentina
August 30, 2012
Q. Can anyone guide me to the “methods of analysis for quality control of boric acid?” I am seeking to get a homemade product registered with the Belize Pesticide Control Board… and the application requires this data. Any help and guidance would be most appreciated!
Denise Frank
– Belize City, Belize
September 20, 2012