analysis of boric acid by LC-MS

[emanuele.scollo]

Dear All,

I am trying to analyse boric acid with an ESI source in negative mode. I am using ammonium formate (pH 8.4):acetonitrile 95:5 as mobile phase at a flow rate of 0.25 ml/min as mobile phase. I first tried direct infusion, that it is injecting with no column but I could not get this compound to ionise.
I would grateful if you could advise whether any of you has had any experience of analysing boric acid by LC-MS or refer me to any published method in the literature.

Thanks

[Jetjamnong]

Try to derivatise with some organic compounds such as Triethanolamine and find the new one compound.
Please see the following link for your guidline, http://www.sciencedirect.com/science/ar ... 0509009635

[dk23]

Dear Emanuele,

Were you able to carry out boric acid LC/MS analysis and if yes, would you mind sharing the conditions you used?

Thank you.

[Alp]

I did a quick search and found something interesting:

according to the boric acid wiki

There are conflicting interpretations for the origin of the acidity of aqueous boric acid solutions. Raman spectroscopy of strongly alkaline solutions has shown the presence of
B(OH)4−
ion,[3] leading some to conclude that the acidity is exclusively due to the abstraction of OH– from water:[3][4][5][6]


Might explain your problem.

Alp

[JMB]

Boric acid can form cyclic borates with polyhydroxy compounds, e.g. carbohydrates; I suggest that you try a simple mixture (1:1), then "dilute and shoot " approach via direct infusion before actually running LC-MS.

[dk23]

Thank you, JMB. I would like to determine the quantity of unreacted boric acid in a fairly complex mixture, containing polyalcohols as well. The idea would be to determine boric acid in the solvent mixture mimicking the mixture I need to test and then run the test mixture to see if boric acid can be found in it as well. If yes, I would build a calibration curve and determine the quantity.

I find LC/MS to be best suited method as boric acid is not very volatile (boiling point of 300 C). I assume this is a problem as the methods developed for GC are based on derivatization due to low volatility of boric acid. However, I haven`t found any literature on determining boric acid by LC/MS.

I am not sure about other methods - 11B-NMR is not quantitative, FT-IR would be very difficult to read. There are UV methods with curcumine complex, but from what I was reading, curcumine forms a complex with boron and is not able to distinguish amongst different boron-containing molecules - giving a false reading for boric acid.

[JMB]

[quote="dk23"]

I find LC/MS to be best suited method as boric acid is not very volatile (boiling point of 300 C). I assume this is a problem as the methods developed for GC are based on derivatization due to low volatility of boric acid. However, I haven`t found any literature on determining boric acid by LC/MS.

quote]

This paragraph actually contradicts itself. The ready availability of GC/MS methods vs. the lack of a single LC/MS method should tell you something. If you have access to a GC/MS system, consider using derivatization (maybe to TMS ethers); the polyalcohols will give -(OTMS)n and free boric acid should give B(OTMS)3, which will be very recognizable due to strong [M-Me]+ signal with characteristic isotopic pattern due to isotopes of B.