Filtration, gravity

When you re through cooling, filter the crystals on a Buchner funnel. 

Dry them and take a melting point, as described in Chapter 9. 

If you find yourself with a flask full of hot solvent, your product dissolved in it, along with all sorts of trash, this is for you. You ll need more hot solvent, a ringstand with a ring attached, possibly a clay triangle, some filter paper, a clean, dry flask, and a stemless funnel. Here s how gravity filtration works. 

Fold up a filter cone out of a piece of filter paper (Fig. 42). It should fit nicely, within a single centimeter or so of the top of the funnel. For those who wish to filter with more panache, try using fluted filter paper (see world famous fan-folded fluted filter paper, Fig. 52). 

Get yourself a stemless funnel, or, at least, a short-stemmed funnel. Why Go ahead and use a stem funnel and watch the crystals come out in the stem as the solution cools, blocking up the funnel (Fig. 43). 

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Tneory of Centrifugal Filtration Theoretical prechc tions of the behavior of sohd-hquid mixtures in a filtering centrifuge are more (difficult compared to pressure and gravity filtration. The area of flow and driving force are both proportional to the radius, and the specific... 

Extremely wet solids (solid floating in water). Set up a gravity filtration (see Gravity Filtration ) and filter the liquid off of the solid. Remove the filter paper cone with your solid product, open it up, and leave it to dry. Or remove the solid and dry it on fresh filter paper as above. Use lots of care though. You don t want filter paper fibers trapped in your solid. 

Fig. 45 A wire triangle holding a small funnel in a large iron ring for gravity filtration.

Set up the gravity filtration and filter off the carbon. It is especially important to wash off any product caught on the charcoal, and it is really hard to see anything here. You should take advantage of fluted filter paper. It should give a more efficient filtration. 

Soil solution samples from saturated soils can be obtained by simple filtration. Simple gravity filtration is preferable to vacuum filtration methods because vacuum filtration can lead to distortions in the composition of analyte composition in filtrates. Syringe filters are usually not capable of handling soil and so are not recommended. Also, some filters can retain analytes of interest. 

Vacuum filtration involves carrying out filtration under reduced pressure and provides a faster method of separating a precipitate from a filtrate than traditional gravity filtration methods. A Buchner, Hirsch or sintered glass funnel can be used during vacuum filtration. 

Any product dissolved in an organic solvent is usually treated with an anhydrous salt such as anhydrous magnesium sulfate. Any water remaining in the organic solvent Is absorbed by the anhydrous substance, which can then be removed by vacuum or gravity filtration. 

Isolation of the products is usually carried out by filtration. Suction filtration is faster and preferable to gravity filtration. When pyrophoric noble metal catalysts and Raney nickel are filtered with suction the suction must be stopped before the catalyst on the filter paper becomes dry. Otherwise it can ignite and cause fire. Where feasible centrifugation and decantation should be used for the separation of the catalyst. Sometimes the filtrate contains colloidal catalyst which has passed through the filter paper. Stirring of such filtrate with activated charcoal followed by another filtration usually solves this problem. Evaporation of the filtrate and crystallization or distillation of the residue completes the isolation. 

A soln of the Ser[PO(OC6H4-2-tBu)2]-peptide H-Leu-Arg-Arg-Ala-Ser[PO(OC6H4-2-tBu)2]-Leu-Gly-OH 3 TFA (5.8 mg, 0.004 mmol) and Pt02 (30.0 mg) in TFA (4 mL) was charged with H2 and stirred rapidly until the cessation of H2 uptake. The platinum was removed by gravity filtration and the solvent removed under reduced pressure. The peptide was precipitated by the addition of Et20 (10 mL) and the solid triturated with Et20 (2 x 10 mL). The crude peptide was dissolved in H20, filtered (20-prn pore)... 

The salt is rapidly removed by gravity filtration, washed with 5 ml of a 1 1 (v v) mixture of absolute ether and absolute alcohol and then with 10 ml of ether. For the next step the moist product is added to pyridine as described below. 

Preparation of the crude aqueous sample extract (Basic Protocol 1) requires 30 min for extraction, 15 min for gravity filtration (-2 min if vacuum filtration is used), and 30 to 40 min for rotary evaporation. This protocol can be completed in less than 2 hr. 

Kiene, R.P. and D. Slezak. 2006. Low dissolved DMSP concentrations in seawater revealed by small-volume gravity filtration and dialysis sampling. Limnol. Oceanogr. Meth. 4 80-95. 

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