Chromatography Forum

Hi 2 every body

How to select the right membrane filter for my application, for example, for mobile phase of Acetonitrile with water which is a hydrophilic reagent, shall I use a hydrophilic membrane or hydrophopic membrane for filtration?

Thank u

I use Nylon-66 membrane filters for acetonitrile, methanol, and aqueous mobile phases.

Depending on the type and amount of organic, some mixtures will pass readily through PTFE as well. You need to try it, then you may have some options.

You also should pass some anlyte through filters, and compare to unfiltered, to make sure all your analyte passes through.

the right membrane depends first of all on the compounds in the sample
after that also the solvent compatibility is important
than you learn that not all membranes are equal and that not all vendors are equal
there are several kinds of PTFEs and PVDFs or Nylons.
in order to see that you have the right membrane you need to check against a sample that was centrifuged and not filtered, and see recovery

there are compounds that will go using whatever (very few)
there are those that will stick to almost anything, triton-X for example
and there are those that will prefer PTFE better than PVDF or the opposite
proteins like more PVDF or PES, amino acids will prefer PES

we use these days filter-vials. great way to make the process easier and faster.
for the bio applications we do the dilution right away within the filter vial.
we know they are going to come out soon with a Nano-vial that will have a very low dwell volume and a maximum pick up capacity.
for the applications that they are suited, they cut down the work time and the amount of workspace and the amount of waste we generate so much that they are very much worth while.
the best thing about them we found out is that they can very well replace most of those very costly GHP and the pre-filters types.
for the UPLCs because it makes us filter the standards and the diluents all the time, we saw we got a lot less dowtime on the HPLCs.
and because in our company purchase was buying the cheaper syringes, without the luer lock design, we cut down the incidents due to sample squirting around, and also the syringe exploding for over filtering