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Is there a general rule of thumb in terms of how one chooses the volume of separatory funnel used for an extraction? It's my understanding that it is the amount of product that determines this as opposed to the volume of the solvent it is present in. If that is correct I was wondering if someone could post what the general ranges in grams of product would be appropriate for the following sep funnel sizes:

250 mL, 500 mL, 1 L

David Reed
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    This is a good question, but it may be hard for it to have one definitive answer. For example, I have always chosen my funnel based on volume of solution. If my compound is dissolved in 100 mL of solvent A and I plan to extract into solvent B, I generally choose equal volumes solvent B (100 mL), and thus the 250 mL funnel. – Ben Norris Jan 20 '19 at 03:55

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If a general rule must be given than the volume of the separatory funnel is mostly dictated by that of the liquid to be treated.

Indeed is better to extract the product by repeating several steps each using small portions of extracting solvent. This ensures a more efficient extraction based on repartition, I.e. a more quantitative recovery of the product as well as a more convenient work-up (cost-effective, less time consuming, less waste).

I am not considering difficulties due to a slow phase separation which might prevent the use of a narrow funnel but in general use the smallest that allows an easy shaking and inter mixing. (When you get to know the actual separation you might even prefer a specific funnel shape not just that V).

Example: 200 ml to be treated with three to four 25 or 50 ml portions : 500 ml funnel.

Alchimista
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