Formic Acid Quantitation

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jn2008
jn2008's picture
Formic Acid Quantitation

Hi all,
I am trying to quantitate formic acid by GC-FID(PE Clarius 600) by converting formic acid in to methyl ester using acidified methanol. Does anybody know what acidified methanol specifically means? Is any acid good for it at any concentration? The abstract that I am following does not have details.
Please help!!

John Bland
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That usually means HCl

That usually means HCl/Methanol. You can purchase this from Sigma-Aldrich or you can make it by this procedure:

HCl-methanol – HCl gas was generated by dropping concentrated sulfuric acid on reagent grade sodium chloride. The HC1 gas was then bubbled through methanol until 5-10% in methanol was obtained as determined by titration.

Heat in a sealed vial at 50oC for 5-10 min.

jn2008
jn2008's picture
Does it mean that combining

Does it mean that combining the acid with Methanol will not work?
I was trying to make a 0.01M solution of HCL in both Methanol and Ethanol to methylate formic acid.

Dr. Analytical
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The acid you would use (e.g.,

The acid you would use (e.g., conc. HCL) is still mostly water, which can reduce the reaction yield. Anhydrous conditions are best.

You can also make methyl esters with BF3/Methanol. This combination is also available from Aldrich. I think the reaction conditions are a little milder. I know this method is used for fatty acids.

huiqi
huiqi's picture
sorry to bug in. i'm also

sorry to bug in. i'm also trying to come up with a method for formic acid quantification. i tried to make methyl formate using 2N KOH (what i used to methylate my fatty acid) and apparently it doesnt work. was thinking to use methanol + sulfuric acid, i read that 5% of sulfuric acid can force the formation of methyl formate but my fear was that the conc of sulfuric acid seems to be too high and i'm afraid that it might spoil my gc column.

hope that we can all share our findings and i really need the help of you guys :) thanks a lot in advance!

(edited) there was a typo error. i mean 2N methanolic KOH. sorry about it :D

Dr. Analytical
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A strong base such as OH is

A strong base such as OH is going to hydrolyze acids. You generally digest/saponify/hydrolyze biological adducts to release the acid. However, this does not create the ester. You need a methyl group to do that.

Carboxylic acid + alcohol, with an acid catalyst, will create a methyl ester, but the reaction is an equilibrium situation, and may not go to completion.

And remember, methyl formate has a bp of 32 C, so if it does form, it will evaporate quickly. And if you are using GC, it is likely to elute with the solvent, unless you are doing headspace.

There are several ways to make methyl esters. The following like gives a list.

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Write back if you have more questions.

Dr. Analytical
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Here's another thought.

Here's another thought.

The following link lists a set of different BF3/alcohol combinations from Aldrich.

In particular, you might try the BF3/butanol. This would produce a butyl ester which would have a higher bp, and would be easier to separate by GC.

huiqi
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is it possible if i were to

is it possible if i were to make my own BF3/alcohol? because of my budget constraint.

jn2008
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Hi everyone,

Hi everyone,
Thank you so much for all your suggestions.

huiqi,
Today I worked on the method development and used 0.001M alcoholic Ethanol as my diluent to convert Formic acid to Ethyl Formate. The column used was DB-FFAP. I injected a stock of Ethyl Formate in acidified Ethanol to confirm the RT.
Try it!!

huiqi
huiqi's picture
ic. thanks a lot of the helps

ic. thanks a lot of the helps from you guys (esp. Dr analytical, jn2008 and Dr john). i will give it a try next week. :)

thanks! have a nice week ahead!