Chromatography Forum

I use Waters Spherisorb ODS-2 column (4.6 x 250 mm; 5 um). Column is 4 months old. Mobile phase is 10% methanol:90% water. Column shipping solvent was acetonitrile. At the beginning of my work, my supervisor told me I could wash column in methanol at the end of day (and leave it in methanol). 3 weeks ago I start washing and keeping my column in acetonitrile. I wash column for 30-45 minutes (flow = 1 ml/min) at the end of day, with acetonitrile. 2 weeks ago I noticed increase in retention time of my analyte - each day I had changes in retention time. Now my analyte has retention time 11 minutes, and 3 weeks before, retention time was 5 minutes. I have cca 30 injections per week. What can I do to decrease RT ?
Thanks for advice.
Veronika[/img][size=9][/size][size=12][/size]

What is the nature of your analyte? Is it a basic compound?

The analyte is 5-hydroxymethylfurfural (HMF; CAS.no: 67-47-0).

In order to bring the retention back to where it was, increase the methanol concentration in the mobile phase.

Thank you very much for the answer.

OK, I'll increase methanol in mobile phase.
What do you think, should I wash the column in methanol instead of acetonitrile ?

I would continue to store the column in acetonitrile.

Thank you very much for the answer.
Best regards,
Veronika