Chromatography Forum

I'm running an analysis once a day at a different location using a Nova-Pak C-18 column and a mobile phase of methanol/water (30:60) with one percent acetic acid. There isn't time to flush the mobile phase each day and replace it with methanol/water. Is it safe to just shut off the flow when I'm not analyzing and leave the column in the acetic acid mobile phase?

I run almost the same mobile phase and have instruments idle for a couple of days every few weeks. I haven't seen any detrimental effects. As long as the sample components have eluted completely, you probably don't need to worry. I replace my columns every 6 months as a preventative measure but that's after 7000+ samples.

We oftentimes leave mobile phase with 0.4% acetic acid in the aqueous phase in the columns for weeks or longer. No issues.

When I am using the same mobile phase every day, at the end of the day I flush the column with pure solvents. For example, if i'm using metanol/water with one percent acetic acid, at the end of the day I would flush the column with the same ratio of metanol and water (but pure,without acetic acid).
I think that kind of column care can prolong the column lifetime, although acetic acid does not make problems at the moment.

Best regards
Zoran

We only flush if we have dissolved solid modifiers in the mobile phase. That's one reason we only use such solid modifiers 10% of the time (only when really needed).

Thanks for the replies. You've set my mind at ease and saved me a lot of extra work. Usually I do flush out the columns after the analysis is complete but in this case it would be very inconvenient to do so. Isn't this forum great?