Burette, PTFE Key

Quick Answer: A PTFE key burette is a graduated glass burette whose stopcock plug is made of PTFE instead of glass. PTFE needs no grease and does not seize, so the burette suits alkaline titrants and routine titrations without stopcock maintenance.

Why a PTFE Plug Replaces Glass

The stopcock is the part of a burette that gives the most trouble. A glass key must be greased to turn smoothly and seal, the grease can creep into the bore and tip, and alkali solutions can cement a glass key in its barrel. A PTFE key burette avoids these problems because PTFE (polytetrafluoroethylene) is slippery, resists almost all laboratory reagents and does not bond to glass, so the key turns freely without lubricant.

The key is usually held in the glass barrel by a threaded nut and washer on its narrow end. Tightening the nut presses the tapered plug into the barrel to stop leaks; loosening it lets the key turn more easily and allows it to be removed for cleaning. PTFE is softer than glass and can slowly cold-flow, so the tension may need a small adjustment from time to time.

This makes the PTFE key burette the practical choice for sodium hydroxide titrant, for student benches where grease tends to be over-applied, and for titrations in which grease would contaminate the delivered liquid.

Care & Handling

• Do not overtighten the retaining nut; a key clamped too hard is stiff to turn and can crack the barrel.
• Remove the key before drying the burette in an oven, because PTFE and glass expand differently and the key may loosen or distort.
• Wash the key and barrel separately and check the bore for particles that would block delivery.
• Store burettes vertically in a burette stand or flat in a padded drawer, never leaning where they can roll.

Applications

• Acid-base titrations with sodium hydroxide titrant, which would seize a glass key
• Student titration practicals where no stopcock grease is wanted
• Non-aqueous titrations in organic solvents, which dissolve stopcock grease
• Redox titrations with potassium permanganate or iodine, which rule out rubber-tube burettes

Specifications

Why Choose LabEquip

College chemistry departments, pharmacy laboratories and schools replacing seized glass-key burettes often switch to PTFE keys. LabEquip lists this burette alongside the straight bore glass key burette in its chemistry lab equipment range; send sizes and quantities through the contact page.

Frequently Asked Questions

Does a PTFE key burette need stopcock grease?

No. PTFE is naturally slippery and seals against the glass barrel without lubricant. Adding grease is unnecessary and can make the key slide out of position or contaminate the tip.

Why is a PTFE key better for sodium hydroxide?

Alkali solutions slowly attack glass and, when they dry in a ground glass joint, can fuse a glass key to its barrel. PTFE does not bond with glass or react with alkali, so the key stays free even if some solution is left in the burette.

My PTFE key is leaking. What should I do?

Check that the washer and nut are in place and tighten the nut a little at a time until the leak stops while the key still turns smoothly. If it still leaks, look for scratches on the key or particles trapped in the barrel.

Can the key be taken out for cleaning?

Yes. Unscrew the nut, remove the washer and draw the key out of the barrel. Wash both parts, keep the small pieces together, and refit them before the burette is next used.

Is a PTFE key suitable for organic solvents?

PTFE resists almost all common solvents, so it is often chosen for non-aqueous titrations where grease on a glass key would dissolve into the titrant. Check that any plastic nut or washer also resists the solvent used.

How do I read the burette accurately?

Clamp it vertically, bring your eye level with the bottom of the meniscus and read against the graduations, estimating between the smallest marks. A white card with a black strip held behind the burette makes the meniscus sharper.

Last Updated: September 2026