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huiqi's picture

Hi guys, i ran formic acid analysis using LCMS (ESI) that day and when i was using purified H2O as my mobile phase, there wasn't any peak of formic acid but when i changed the mobile phase to 0.1% TFA in water, i was able to recover the formic.

I'm not very sure of the theory behind, can anyone please enlighten me with regards to the observation mentioned?

Thanks ;D

Dr. Analytical
Dr. Analytical's picture
We need a little more

We need a little more information on your system. What column were you using? What were the ESI parameters?

Formic acid is a "weak" acid, and so would be ionized at neutral pH. The format ion will have little retention in reversed phase LC; it probably eluted in the void volume. In acidic solution, the formic will be neutral, which gives it somewhat more retention. However, it is still quite polar and is barely retained on most systems. There are some "acid analysis" columns that will retain it along with other acids.

And then there is TFA itself, which is known to cause some unusual ion pairing effects.

Write back with more details and maybe we can come up with an explanation.