Speed of Mobile Phase filtration

<p>Filtering of 10mM Ammonium Formate (95:5, H20:ACN) through a 0.2 um nylon filter is extremely slow. Any tips on filter composition, filter technique to increase the speed of filtration. Is 0.2 um filter necessary or is larger pore size recommended?</p>


  • How much solvent are you filtering? How are you doing it now? What is the source of your water?


  • 500 mL (poured in all at once).

    Filtration under house vacuum.

    18.2 millipore Barnstead system.

  • I assume that your water purification system has a 0.2 um filter at the point of use. Most water purification systems have a filter on the outlet of the unit. If you are unsure, contact the manufacturer. As this is likely the case, there is no need to filter the water (by itself).

    Also, your ACN is most likely filtered as well. Therefore, there is no need to filter this either. Frankly, I suggest you NEVER filter organic solvents because 1) there is no need to; 2) possible incompatibility with the filter material.

    Here's what I am getting to. Dissolve your buffer salt in as little ultrapure water as possible. Filter that only. Then add the remaining ultrapure water, adjust pH, add your ACN, etc. as you normally do.

    This is the best and fastest way to filter the aqueous portion of your mobile phase, assuming you are working with high quality, previously filtered solvents and water.

    I hope this helps.


  • Doug, thanks very much for the recommendation!

  • Hello

    Here is another thought, if you still need filtering, place two filters in line the first being 0.45 and then 0.22 and it will go faster!


  • Liz, thanks a lot for suggestions.

    We thought again if there is a need to filter the mobile phase although it has been recommended in some of Waters training slides for Acquity. We think as long as the grades of reagents used for buffer mobile phase are high and the salt can be easily dissolved, the likelihood to clog the tubing is not that much. But we do need to be extra careful when switching between mobile phases to avoid any clog due to precipitation.

  • Yes, I do agree!