Chromatography Forum

For a few tests in our lab we use Water w/ 0.1% Formic Acid and MeOh w/ 0.1% Formic Acid. We regularly get a low result for our quality control checks on our products so I am trying to see if has something to do with a problem on our end. Recently I read this article (http://www.chromatographyonline.com/sta ... 9&pageID=2) which says that formic acid degrades fairly quickly in MeOH. Is this a normal problem that anyone here has seen occur? How has it affected your results/runs?

Also, we purchase a premixed MeOH/0.1% Formic Acid solution from Honeywell here: https://shop-lab-honeywell.com/methanol ... cid-14276/

If degradation of Formic Acid is a known issue, why would they sell a premix? Should we just prep our own frequently enough to not worry about this as an issue?

Thanks.

Acid loss of formic acid in Methanol is a well documented issue. The pH changes over time (days), This can directly effect the method and results. Solutions should be made up fresh daily (specifically formic acid in pure methanol). Not recommended to every buy pre-mixed bottles of methanol with formic acid! What were they thinking?

We get a lot of questions about this during the classes we teach. This is an upcoming topic on the HPLC hints and tips blog ( https://hplctips.blogspot.com/2019/09/a ... ormic.html )

Thanks! Is there any similar issue with TFA in MeOH? We are thinking of switching to that

No, not that I am aware of. However, TFA is an extremely strong acid, grossly overused in our industry (often without purpose, because the person before them always used it). For any LC/MS applications, avoid the use of TFA or any strongly ion-pairing agents. Formic acid or high purity acetic acid are better choices. For non-MS applications, if you must, please use the lowest possible concentration of TFA that gets the job done (less then 0.1%, perhaps 0.05 or 0.01%).

That said, preparing freshly prepared mobile phase each day is routine and should not inhibit you from using 0.1% formic acid in Methanol if that is what works best for your application. Prepare only what is needed for the day.