Buchner funnel filtration as an alternative to micron filters

[seep]

(I would put this in OD except that it has the word Buchner)

I actually just ran across Captain Heroin's excellent Micron Filtering Megathread. The early and predictable objection some people had there is that there's a lot of stuff to buy, and keep buying, and keep buying. My reaction was a bit different and had a lot to do with maximizing yield.

I'm wondering whether anyone has gotten mileage out of converting pills to gook-free IV solutions with a Buchner funnel.

This fucker here retails for $50:

Obviously the only thing you need to repurchase are the filters. The porcelain funnel is 125 mm in diameter, and so is quite capacious. Or, if you don't need to entertain Wrigley Field, you can buy a much smaller model cheaper.

 

[Black]

i imagine won't work nearly as good. filter papers that are as fine as micron filters (if they exist) would be expensive. besides that you would also need a good vacuum pump and furthermore there'd be a much greater chance for contamination.

 

[xxl]

This would only work for bigger quantities of liquid.

Remember that micron filters are 3D structures, they work like several filter papers stacked upon one another.

 

[mimac]

The buchner filter sucks up a lot of liquid (up to 10 mL)!

Consider using a syringe micron filter like this:

http://www.shelfscientific.com/cgi-...vb.ukz&lpg=/lab/filtration.tam&lpt=1243468531

Usually you can find them at less than 0,5$ per piece (if you buy in bulk). For volumes less than 3 mL you can buy the 0,5 cm diameter filter, for more than 3mL (up to 5-10 mL) take the 3cm diameter ones.

The 0,2 um should catch all bacteria and most of the spores. The problem is that it clogs up quite quick!

 

[xxl]

The 0,2 um should catch all bacteria and most of the spores. The problem is that it clogs up quite quick!

This is why prefiltering is necessary. I wonder whether using a 0.45 + 0.22 in sequence is a better option than using cotton + 0.22. What I would be worried about is the retention. You don't want half of your liquid to remain in the filters.

 

[Ylide]

A standard buchner setup is probably better suited to being used as a prefiltration step. If money isn't an object, there are glass fritted filter assemblies that take large size membrane filters available. They're usually used in the preparation of HPLC solvents. However they are rather expensive and rather fragile.

 

[mimac]

This is why prefiltering is necessary. I wonder whether using a 0.45 + 0.22 in sequence is a better option than using cotton + 0.22. What I would be worried about is the retention. You don't want half of your liquid to remain in the filters.

The best option IMHO would be a coarse filtration + 0,2 u filtration and then washing with pure solvent (water/saline/weak acid).

 

[seep]

i imagine won't work nearly as good. filter papers that are as fine as micron filters (if they exist) would be expensive.

Yep. I'm seeing 0.7 micron (pore size) sheets running at about $1.64 a piece (glass microfiber).

There's a Japanese supplier that sells 0.3 micron pads for filtering sa-ke. I can't tell what the price is. They're made from cellulose fiber and "diatomaceous earth". The 0.3 micron aspect doesn't refer to pore size, but rather to experimentally-determined retention (using precipitated barium sulfate).

I suppose I can't just get some kind of specialized stock from Home Depot and go at it with a bandsaw.

The advantage of a flat, open ceramic filtration vessel is versatility. You can do successive hot and cold filtrations, multiple washes, etc. An aspirator would provide a ready vacuum source.

 

[MurphyClox]

Büchner-funnels (with "ü", not "u" ) are definitively not fine enough to provide sterile filtration resp. the ones with a suitable fine pore-size usually need proper vacuum equipment. But, as was already mentioned before, they suffice for pre-filtration of samples so that the micron-filters do not clog this easily.

I would recommend the following setup:

Use glass frits for micro-scale work, like those:


Instead of the usual vacuum flasks as shown in the picture in post #1, use such modified test tubes instead:

(without the screw cap, of course)

Vacuum can be applied with a simple aspirator

This works for very small quantities like 1-2 ml without any considerable losses. Before injecting use a micron-filter to ensure sterility!!!

Glass frits are available in the following sizes:
G00 (250-500 µm pore size)
G0 (160-250 µm)
G1 (100-160 µm)
G2 (40-100 µm)
G3 (16-40 µm)
G4 (10-16 µm)
G5 (1.0-1-6 µm)

On the american market sizes are often designated as follows:
Extra coarse (170-220 µm), coarse (40-60 µm), medium (10-15 µm), fine (4-5.5 µm), very fine (2-2.5 µm) and ultra fine (0.9-1.4 µm).

For comparison: Sterile filters for syringes have a pore size smaller than 0.2 µm!

Usually G4 is fine enough for all visible precipitates; with G5 it is already quite difficult to suck any aqueous solution through it due to the high surface tension of water. In other words: A plain aspirator is not suitable anymore.


Cheers! - Murphy

 

[negrogesic]

Its good for larger volumes. Also, its a good idea to run your solution through a 1.2 or 2 micron filter first, then run it through a .2 micron filter. This prevents clogging of the .2 micron filters. Obviously, you may yield less, which can be compensated by additional drugs....

 

[xxl]

So you would say running it first through a 0.45, then through a 0.22 micron filter would not be that great, owing to the difference in pore size being too small between 0.45 and 0.22?

 

[negrogesic]

^^^Yes, that would result in more waste. If you filter first through something 1.2-2 micron, then the resulting solution will pass quickly through the .2 micron filter and will not clog.