Chromatography Forum

Does the needle wash has to be same organic used in M.P.? For example we have Acetonitrile/H2O 80/20 as our M.P. B, do I have to use Acetonitrile(or acetonitrile/H2O) as needle wash or can I use methanol instead?

Thanks!
Apple

It depends. The solvent used for the needle wash should be compatible with your mobile phase, your sample, and impurities you wish to wash out. It should also not cause any background issues with your detector settings. That said, methanol could be used with an acetonitrile/water mobile phase as long as it does the job of washing out the carryover and not causing sample precipitation.

I have always used 30% methanol in water for needle rinse/wash, and it seems to work fine with most mobile phases. Of course, of methanol is known to be completely incompatible with your particular mobile phase, you should probably avoid it.