Hi Ryu

After ethanol fixation you can store your sample in -20C for a month.

While running make sure to remove ethanol by washing it with PBS .

I usually store EtOH-fixed cells at 4°C for weeks, sometimes months, and it still works (detection of BrdU, EdU, PI/7-AAD), although I never actually compared the same samples before and after long storage to check for signal loss.

I agree with Vincent,

the importance is not to compare the samples before and after long time storage, if not to compare all the samples from a single experiment using the same parameters (i.e. the same time of storage), where some hours more or less are irrelevant. Yo can store them in ethanol for weeks (more than 4).

Thank you all for your helpful comments.

Indeed, you can store the ethanol fixed cells at low temperatures for a long time, at 4 degC for a week and at minus 20 for one to two months. However, staining with propidum iodide should be done fresh before acquiring the cells on a flow cytometer.