I was wondering if someone could enlighten me on some example us cases where one would be better of using a Buchner funnel with a fritted disc (example), as opposed to a Buchner "style" filter (example) that requires a filter paper (example).

A few times in the past when I was looking to filter a specific substance and asked about fritted discs, most of the replies were "don't use a fritted disc, just use a funnel with the filter papers instead," and this got me wondering when using a fritted disc would be preferable over a filter paper. Originally, in my chemistry naivety, I mentioned that I may end placing a filter paper inside a Buchner funnel with a fritted disc, to "get the best of both worlds" I suppose, but this idea was shot down pretty quickly.

Heres the pros/cons list for both filter types that I have thus far, hoping some can add to it:

Buchner "style" filter with filter papers

  • Pros
    1. The filter papers are cheaper
    2. Changing the filter paper pore sizes are much easier, as it's just a matter of getting the filter papers with the desired pore size
    3. One can easily cut the filter papers to the proper diameter if needed
  • Cons
    1. ??

Buchner filters with fritted discs

  • Pros
    1. Filters are reusable if cleaned properly
    2. ???
  • Cons
    1. Fritted discs are much more expensive than filter papers
    2. Fritted discs don't seem to have specific pore sizes
    3. Fritted discs seem like they can be a pain to clean properly

Thanks in advance for any input!

  • 2
    $\begingroup$ You say "filter papers" but there are Buckner filters made from glass fibers. // A filter is a filter. All sorts of filter materials and filter apparatus types are available. eg Micropore's offerings // Obviously you don't want filters or filter apparatus for solutions that would be attacked by solution being filtered. For example using a paper filter to filter a conc. sulfuric acid solution would be a bad idea... $\endgroup$
    – MaxW
    Jul 16 '18 at 16:58
  • $\begingroup$ @MaxW - I linked to examples of exactly what I was referring to. $\endgroup$
    – Justin
    Jul 16 '18 at 17:20
  • $\begingroup$ Fritted Glass is easy to clean with warm Iso. $\endgroup$
    – user87886
    Jan 13 '20 at 3:42

Buchner + filter paper cons:

  1. The filtering surface is not uniform. It filters only where the holes are, so most of the surface is not working.
  2. Some solid can slip between the paper and the filter. Then the filtrate must be filtered again.
  3. You have to cut the paper.

Fritted glass filter pros:

  1. Uniform filtering surface.
  2. Pore sizes from number 1 (coarse) to number 4 (fine). In organic chemistry, number 3 is the standard.
  3. Can be cleaned easily when the solubility of the product is known.
  4. Can be sterilized at high temperature.

I use them almost for everything except for filtering activated carbon and very dirty unknown samples. If the solid does not dissolve in solvents, we try with concentrated caustic, concentrated sulfuric acid or strong oxidants; in that order.

It is better to buy the ones without the vacuum connection. They are cheaper and have less points where they can break.

  • 1
    $\begingroup$ easy enough to add a layer of Celite too which will catch very fine particulate. I always use this for catching hydrogenation catalysts on carbon $\endgroup$
    – Waylander
    Jul 18 '18 at 10:28
  • $\begingroup$ True. But if it is not enough or you get a channel it will reach the fritted glass. And then, when you filter a white solid it always get stained. $\endgroup$ Jul 18 '18 at 10:31
  • $\begingroup$ What if you're filtering a known sample, but its the filtered residue you're after, not the filtrate? And if the residue is in a powdered form? And does it matter if its a base? $\endgroup$
    – Justin
    Aug 3 '18 at 16:46
  • $\begingroup$ Edit: Looks like I could just place a Celite pad on top of the frit, interesting. $\endgroup$
    – Justin
    Aug 3 '18 at 17:05
  • $\begingroup$ Raoul Kessels - If I want to filter out charcoal powder using a fritted disc, as long as I use celite or diatomaceous earth for padding, I should be fine, correct? I know its a bad idea to use charcoal powder with fritted discs (super difficult to clean afterwords), but I think it should be fine if I just create a padded layer. Right? $\endgroup$
    – Justin
    Nov 4 '18 at 20:33

I have been a synthetic chemist for 10 years and i would strongly recommend to avoid using fritted disks for performing any filtration. In the above answers some points are correct and some others not so much. Therefore i will summarize here:

Filter paper advantages:

  1. Low price.
  2. Variable filtering capacity, up to extra fine by using glass microfiber filter papers (only a couple of times in 10 years i had precipitates that managed to pass a glass microfiber filter paper).
  3. Can be cut to any size and shape.
  4. Can be purchased as circles to sizes that will fit the funnel so cutting is not necessary.
  5. It is disposable, so there is no chance for contamination with material from the previous filtration.
  6. The buchner funnel is easy to clean after use.
  7. Can be easily used with silica or Celite to ensure extremely fine solids dont go through.
  8. Can be sterilized: I have kept normal filter paper in a 180 C oven for several hours. It just turns slightly brown but the filtering capacity doesnt change. Glass micro fiber paper of course can be kept infinitely in the oven without any problems.
  9. Has other uses as well such as folding it for use in funnels for gravity filtration or use in cannula filters.

Filter paper disadvantages:

  1. Can get ripped, and if one scrubs the surface for reclaiming the last trace of solid one can contaminate the product with paper fibers.
  2. As Raoul mentions, some solid can slip between the paper and the filter. However i consider this a mistake form the users side since it wont happen if the filtration is set up properly (had it a few times and it was my mistake in all cases).

Fritted discs advantages:

  1. Less setting up, can be used straight away.
  2. Reusable (?).

Fritted discs disadvantages:

  1. More expensive.
  2. Fragile.
  3. Cant be used for cannula filtrations.
  4. And the biggest issue of all: THEY ARE A NIGHTMARE TO CLEAN. Eventually they will get clogged with all sorts of solids from the various filtrations where one keeps the solution and discards insoluble precipitates. After that point they are practically useless since they could contaminate your filtrate with whatever is stuck in the pores. We had success cleaning blocked frits like that by leaving them in the basebath, but eventually they dissolve making them less effective as filters. The way around this is to use silica or celite but eventually the particles will also get stuck in there (along with whatever else is adsorbed on them). Use of celite also beats the purpose since it is like adding a filter paper to it.

I only use fritted discs (coarse size) in combination with a syringe (had the glass blower fit it in the bottom of the syringe) along with a layer of glass microfiber paper and celite for quick filtrations of small amounts of suspensions. Works like a train toilet.


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