What is the difference between a volumetric pipette and a volumetric flask?
A volumetric pipette delivers one fixed volume of liquid, while a volumetric flask contains one fixed volume and is used to prepare solutions of a precise final volume. The pipette is calibrated to deliver (TD), and the flask is calibrated to contain (TC). They are often used together when making dilutions.
What each piece of glassware does
A volumetric pipette has a long thin stem, a central bulb and a single graduation mark above the bulb. You fill it just above the mark, adjust the meniscus to the line, and let the liquid drain freely into another vessel. The tip is touched to the inner wall for a few seconds, and the small amount left in the tip is not blown out.
A volumetric flask has a flat base, a wide pear-shaped body and a long narrow neck with one ring mark. You add the solute and some solvent, dissolve it, then top up carefully until the meniscus sits on the ring. A stopper allows you to invert and mix the contents thoroughly.
Key differences
| Feature | Volumetric pipette | Volumetric flask |
|---|---|---|
| Calibration | To deliver (TD) | To contain (TC) |
| Purpose | Transferring an exact volume | Preparing a solution to an exact total volume |
| Typical sizes | 1 to 100 ml | 5 ml to 2 litres |
| Mark | One mark on the stem | One mark on the neck |
| Draining | Allowed to drain, tip touched to wall | Not emptied for measuring; contents poured out as needed |
| Storage of liquid | No | Not for long-term storage |
Why TD and TC matter
When liquid drains from glass, a thin film stays behind. A TD instrument is calibrated with that film in mind, so the volume that leaves the pipette is the stated volume. A TC instrument holds the stated volume when filled to the mark, but the amount you can pour out is slightly smaller. For that reason you should never use a flask to measure out a volume by pouring.
Both are marked with a temperature, usually 20 degrees Celsius, because glass and liquids expand with warmth. Using them at a very different temperature adds a small but real error.
Using them together
A common routine is making a diluted standard. You pipette a precise aliquot of stock solution into a volumetric flask, add solvent until the meniscus touches the mark, stopper the flask and invert it several times. The pipette fixes the amount of stock taken, and the flask fixes the final volume, so the dilution factor is known accurately.
- Rinse the pipette with a little of the stock before filling it.
- Do not rinse the flask with the stock; a little water inside does no harm because you are adding solvent anyway.
- Add the last few millilitres of solvent with a dropper or wash bottle to avoid overshooting.
- Mix by inverting; do not shake with the mark unobserved.
Accuracy
Class A glassware has tighter tolerances than class B. A 10 ml class A pipette is typically accurate to about 0.02 ml, and a 100 ml class A flask to about 0.08 ml. Those figures are for guidance, and the exact tolerance is printed or specified in the relevant standard. Cleanliness is essential: grease on the inside surface causes droplets to cling and distorts the meniscus.
Vanliga frågor
Can I use a volumetric flask to store a solution?
It is better not to. Flasks are made for preparing solutions, and long storage can contaminate the liquid or etch the glass. Transfer the solution to a suitable labelled bottle.
Can I heat a volumetric flask?
Avoid it. Heating and cooling can change the glass volume permanently, which ruins the calibration.
Why do I not blow out the last drop of a volumetric pipette?
The calibration already accounts for that small remainder, so blowing it out would deliver slightly too much.
Choosing droppers for your product
Laboratory pipettes and flasks are precision tools. A dropper on a product bottle works differently: it is an assembly of a glass pipette, a teat and a collar that dispenses liquid in drops and is not calibrated to a certified volume. Packaging.si assembles DIN18 droppers in Slovenia and supplies matching amber glass bottles from 5 to 100 ml.
