dangerous amateur
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Coffee filter vs. "folded" filter papers from lab supply
Hi guys,
how much better are in your opinion/experience the special lab filters?
Coffee filters seem to clog very quickly and let fine stuff through.
I recently used one for getting a barium sulfate suspension out of a solution (I know thats hard stuff for any filter) and the coffee filter did not
do a good job.
Lots of milk got through and i took a very long time 
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chemcam
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That is probably why professional labs use one of many types of lab filters not just one type.
Coffee filters are just that, COFFEE filters. There is not one filter that's fits all requirements. You have to think about size, material, chemical
resistance and the like.
If you look around this board you will find a post by Dr. Bob who gives a great explanation of filter usage.
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Dr.Bob
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There are many types available, but I have used coffee filters the same way. They work well for some things. I do have a very limited number of
filter papers available, but there are also many types available on Ebay, Amazon, and other sites.
For use with glass stems liquid funnels, I like the prefolded or pleated papers. They generally work well and are simpler than trying to fold flat
paper well, which never works as well as I think it should, since it seems easy in theory. For buchners, the premade circles are nice, they sell
them in thin (fast), medium, and thick - I have never used the thick, they clog instantly.
Bob
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amazingchemistry
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Per Vogel's Textbook of Quantitative Chemical Analysis:
"Colloidal properties are, in general, exhibited by substances of particle size ranging between 0.1um and 1 nm. Ordinary quantitative filter paper
will retain particles down to a diameter of about 10^-2 mm or 10um, so that colloidal solutions in this respect behave like true solutions and are not
filterable (p. 419)"
Thus, if your suspension is a true colloid (as it very well may be) full separation using filter paper is next to impossible. Have you tried salting
out?
Always remember to check your pride at the door and ask that "stupid" question. Learning comes from having your "stupid" questions answered.
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bfesser
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Celite™ (<a href="http://en.wikipedia.org/wiki/Diatomaceous_earth#Filtration" target="_blank">diatomaceous earth</a> <img
src="../scipics/_wiki.png" /> works wonders.
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Fantasma4500
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even cloth filters as of bedsheets can do as far as 1 micron, plus it goes very fast filtering and its not that easy to break
the only times i dont use cloth filter is when i have something thats very small where i dont want to loose the liquid at all (gold refining)
i did however see once a plastic/rubber coffee filter
dont know if i can get a hold of that thing anymore, it would me somewhat hard to shape as its plastic / rubber, but its chemical resistance would
plausible be very high, although paper is already pretty high
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Mildronate
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you dont need funnel for cofee filter, thats way i sometimes use it, but actualy the best opinion is vacum filtration and forget about cofee filters
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dangerous amateur
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Im going to expand my means soon.
I allready have a small buchner + a set op papers, but i was simply to lazy to use it, because i have to improvise, having no proper vacuum equipment.
The vacuum cleaner i use for sucking does of course not pull very good
But a coffee filter is set up very quickly.
| Quote: | | Thus, if your suspension is a true colloid (as it very well may be) full separation using filter paper is next to impossible. Have you tried salting
out? |
I used a pipette and a high cylinder to decant, what worked very well. I estimate losses to be less than 10%.
<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: fixed quote
tags]
[Edited on 7/14/13 by bfesser]
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bfesser
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The definitive answer, as <strong>chemcam</strong> hinted at, is that there is no "magic bullet." You need the right filter, funnel, and
technique for the job. Gravity filtration is generally better to clarify a filtrate, vacuum filtration is often preferred for the filtrant. Paper
works in some cases, glass fiber in others, and sometimes a filter aid is desirable.
I even have different types of syringe filters for special occasions.
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