Pear-shaped Separating Funnels

A separating (or separatory) funnel is the tool for liquid-liquid extraction. Two immiscible liquids — say an aqueous layer and an organic solvent — are shaken together in the funnel so a compound transfers into one phase, then allowed to settle into distinct layers; the PTFE stopcock at the base lets the lower layer be drained off cleanly, separating the two.

The pear or conical shape is functional: it presents a large interface for the layers to settle, and tapers to a narrow point so the boundary between the layers is easy to see and the lower phase can be run off precisely.

Liquid-liquid extraction, organic synthesis work-ups, washing and phase separation, solvent extraction and sample clean-up, in research, teaching, pharma, natural-product and environmental labs.

A pear or conical borosilicate 3.3 body with a ground-glass stopper at the top and a PTFE stopcock at the base leading to a delivery tip. PTFE needs no grease, resists solvents and turns smoothly. The shape promotes clean layer separation, and the stopper seals the top for shaking.

Never fill more than about two-thirds full, support the funnel in a ring stand, and vent frequently while shaking — extractions with volatile solvents or that generate gas build up pressure that must be released through the stopcock with the funnel inverted. Let the layers fully settle before draining, and keep the matched stopper and stopcock with the funnel.

Blown from borosilicate 3.3 into the pear/conical form, fitted with a ground-glass stopper joint and a machined PTFE stopcock, then annealed. Joint and stopcock fit (for a leak-free seal under pressure) and a clean tapered tip are the key checks.