I am having trouble separating formic acid from glycerol since they have the same retention time. My formic acid peak is supposed to be very small as compared to glycerol. I tried 0.2 flow rate at 60 and 70 C. And 0.5 at 60 and 70 C. My HPLC mobile phase is sulfuric acid. Can anyone give me any suggestion on how to resolve this issue? Thanks.