Interesting paper in Chromatographia re: formic acid MP's

[juddc]

Journal: Chromatographia

Publisher: Springer-Verlag

Title: Peculiarities of Mobile Phases Containing Formic Acid

Author(s) Eric Loeser
DOI 10.1365/s10337-009-1001-7
Online since February 05, 2009
Page 807 - 811

It describes how formic acid acts as a co-solvent in highly aqueous MP's due to the fact that only a small percentage of the formic acid in solution is actually dissociated. Also it describes desolvation during acetonitrile gradients, causing a spike (low UV) at the beginning of such gradients.

Not rocket science, certainly but I think something to be aware of for practicing chromatographers.

[HW Mueller]

Do you mean "demixing" as in

viewtopic.php?t=10570

with your "desolvation"?

Do the authors say anything about the dissociation state of formic being dependent on pH?
We have discussed this possible solvation effect of acetic acid some time ago.
Mostly with inorganic acids this sort of thing is apparently addressed via ionic strength.