Chromatography Forum

Hey All, I know phosphoric acid is a fairly common acid used in RP-HPLC, but is it common to get impurity peaks from the H3PO4? I've used two bottles of it, both HPLC grade, and my baseline is never clean for the blank. One MP system I used was just Water/0.2% H3PO4 as MPA and ACN/0.2% H3PO4 as MPB, there the peaks really didn't come off until the end of the gradient, out of the way of any peaks of interest. In another gradient I used the same MPA but 50:50 ACN/IPA 0.2% H3PO4 as MPB, now I'm getting peaks coming out all over the chromatogram (I'm guessing b/c IPA is a stronger eluent). I'm just wondering if this is common with H3PO4 or if it could be something else. This is a new column btw and I'm just running water blanks.

Thanks!

Buffer capacity of H3PO4 is very low, so you don't get an equilibrium on your column. I would recommend to use a real buffer system. Good luck.

"garbage" peaks in gradient blanks are common. The buffer (or phosphoric acid in this case) is one possible source. Others include the water system, contact with pH electrode, or residual detergent. Some time back we did a "mini-seminar" on the problem:
http://www.lcresources.com/more_resourc ... hp?f=3&t=5

You will have to register separately to access it.