Chromatography Forum

I'm curious why you would discard CH3CN after a week. The short lifetime obviously works for you, but your bean counter might be losing a few beans.

Acetonitrile can sit in the manufacturer's bottle for up to 3 years ( Merck HPLC grade ) and still meet specification, and provided your filtering systems don't contaminate it, or the storage bottles allow significant moisture or evaporation, the lifetime should be at least several months.

Bruce Hamilton

We noticed that if we reused AN too long (even though it is filtered every day when the reservoir gets topped up) we had baseline problems. There would be irregular large negative peaks or baseline fluctuations. Actually, irregular is not quite correct. The problem always seemed to appear on or near a peak of interest. Switching to all "fresh" AN would fix the problem. May cost a bit more, but having a large hump or negative peak in the chromatogram was more than slightly irritating. One weird thing is that the problem did not gradually appear. One day it was fine, the next day it was garbage.