"Air Flushing" 13mm 0.22um PES Filters?

[PatchyFog]

I can't remember which other platform it was, but somewhere I came across holdback (I believe) test results comparing several brands of 13mm PES filters. In those tests, both BAC flushing and "air flushing" were used — the latter meaning a seemingly full syringe of air was forced through the filter to clear it once the liquid was done.

While recon-ing today, I figured that seemed like a handy approach, since it would free me from having to set aside reserve liquid for flushing. So once the peps were inside the vial/cart (I was doing both), I detached the syringe from the filter, pulled in a full shot of air, reattached the syringe to the filter, and attempted to drive the air through.

It sort of worked. Roughly 1/2 to 2/3 of the air in my 3 ml syringe went in without trouble, and I watched about 5 or 6 drops of holdback exit the filter and drip into the vial. After that, though, the plunger would not budge any further, and I got the feeling that pushing harder would rupture the PES membrane. The vial/cart was vented, yes, and even after taking the filter/syringe combo off the needle and trying to squirt the air into open air, it still would not push. That makes me suspect the filter material itself swells when air is forced into it, and/or it dries out and turns opaque. (Both Biologix brand and no-name generic.)

Anyway, I'm just wondering whether I "did it right" or whether an air flush requires some special technique I'm missing. I know this way of working is niche; I hadn't heard of it until I read this study. Also, since I'm working in a laminar-flow area, injecting a bunch of bio-loaded room air into the vial worries me less than it otherwise would.

Thanks for any insights.

 

[Aussiegreenmachine]

Based on what I've come across, the 4mm filters respond best to air purging, with roughly 1/3 to 2/3 of whatever liquid is left in the filter making it through. That comes from STG testing, as far as I remember. Those same tests indicated that although a bit of BAC might stay trapped in the filter, most of the peptide still gets pushed into the cart/vial, meaning the result is a marginally higher concentration (ie: not counting the 5 iu or so left behind). The conclusion was that this made no meaningful difference. Personally, I've landed on using air purging for 4mm filters and BAC purging for 13mm filters. TBH so far I've only worked with 4mm filters and they've performed just fine. Should I ever need to filter GHK-cu or a similar compound, I'll reach for a 13mm.

 

[Zelmar702]

If the plunger halts or pushes back while you're injecting air, that's usually a sign the vial has hit its pressure ceiling. Once that point is reached, no additional air can go in. The fix is simply to inject a smaller amount of air.

 

[PatchyFog]

Zelmar702 said:

If the plunger halts or pushes back while you're injecting air, that's usually a sign the vial has hit its pressure ceiling. Once that point is reached, no additional air can go in. The fix is simply to inject a smaller amount of air.

Like I mentioned, the vial had been vented. The plunger still wouldn't budge even once the needle came off (though the filter stayed on). Both of those point to the filter being the source of the resistance.

 

[Chili777]

PatchyFog said:

Zelmar702 said:

If the plunger halts or pushes back while you're injecting air, that's usually a sign the vial has hit its pressure ceiling. Once that point is reached, no additional air can go in. The fix is simply to inject a smaller amount of air.

Like I mentioned, the vial had been vented. The plunger still wouldn't budge even once the needle came off (though the filter stayed on). Both of those point to the filter being the source of the resistance.

All filters come with some level of "dud" rate. That rate varies between manufacturers. If it clogs right away, either you got a dud or it did what it was supposed to. If you've already pushed a couple mL through and got 5 or 6 drops of the hold back volume, I'd call it good with a 4 mm.