Degassing or Filtration

[gregm]

We currently use a glass filtration setup attached to a pump using 0.45um millipore membrane filters. The flask contains a magnetic stirrer. As the solution passes the membrane filter, gas bubbles appears on its surface. As soon as the solution has completely passed through the filter the vacuum pump is turned off and the solution is poured from this setup into another bottle and stoppered until use (up to 3-4 days time). The hplc equipment has inline degassers which are routinely used.

Besides filtering is this setup degassing?

I thought to effectively degas a solution the solution should remain under vacuum for a longer period than the time it takes to filter?

Should we be using this setup to filter/degas HPLC grade solvents or commercial mobile phases?

Thanks in advance

[tom jupille]

Besides filtering is this setup degassing?

Yes, to some extent.

I thought to effectively degas a solution the solution should remain under vacuum for a longer period than the time it takes to filter?

Depends on what you mean by "effectively". In the case of pre-mixed mobile phase, vacuum filtration is probably sufficient. All you have to do is to give the excess air (bubbles) a place to go. In the case of "on-line mixing", the job is a lot harder, because you have to get the dissolved air levels in each component down far enough that you will be below the saturation curve when you mix them. In any case, as soon as you expose the solvents to the atmosphere, they start to re-saturate.

Should we be using this setup to filter/degas HPLC grade solvents or commercial mobile phases?

HPLC grade solvents are typically filtered through 0.2 micron filters at the bottling point.