Baseline issues (again)

[magda roth]

I need to develop an HPLC method for analyzing lactic and C8, C10 carboxylic acids. I am using solvent A: water adjusted to pH 2.5 with Phosphoric acid, solvent B acetonitrile. Unfortunately my baseline shows a major "dip" during the gradient and again is fine at the end, when I have 100% AcCN. I am using HPLC water and acetonitrile from Alfa Aesar - could this be the issue. Suggestions?

[Redi]

Magda:
Can you post the chromatograms? Do you now, at the time the "dip" starts, what are the proportions between A e B?
Try add some acetonitrile to A solution (5% if possible).

[magda roth]

Oh, thanks for your interest. I do not know how to attach the pdf file. Can you give me your e-mail address so I can send it? I am at magda.roth@geagroup.com