What is a dropper in a laboratory?
In a laboratory, a dropper is a simple tool for transferring small amounts of liquid one drop at a time. It is made of a narrow tube, usually glass or plastic, with a rubber or elastomer bulb at the top. Squeezing and releasing the bulb draws liquid into the tube and then expels it as drops. Droppers are used for non-critical tasks such as adding indicator solution, placing a drop of reagent or transferring a small sample.
What a laboratory dropper looks like
A laboratory dropper, also called a Pasteur pipette or a dropping pipette, has a tapered tip and a wider upper end that fits a rubber teat. Glass versions are common because glass resists many solvents and can be cleaned or sterilised. Disposable plastic droppers are widely used where cross-contamination must be avoided. Some bottles for indicators and reagents also come with a dropper fitted to the closure, so that the liquid can be dispensed without a separate tool.
What laboratory droppers are used for
- Adding indicator drops during a titration, such as a few drops of colour indicator in the flask.
- Placing drops of a sample onto a microscope slide or test strip.
- Transferring a small amount of liquid between test tubes.
- Adjusting a liquid level to a mark by adding the last few drops.
- Dispensing stains, buffers and other reagents in teaching laboratories.
How accurate is a dropper?
A dropper is not a measuring instrument. The size of a drop depends on the liquid, the temperature, the shape of the tip and the angle and speed at which the bulb is squeezed. As a rough guide, many aqueous liquids give about 20 drops per ml, but this figure varies widely and should not be used for quantitative work. When you need a defined volume, use a volumetric pipette, a graduated pipette, a burette or an adjustable micropipette instead.
Dropper compared with measuring pipettes
| Tool | Typical use | Accuracy |
|---|---|---|
| Dropper | Adding drops, transferring small amounts | Approximate only |
| Graduated pipette | Measuring variable volumes | Good, depends on class |
| Volumetric pipette | Delivering one fixed volume | High |
| Burette | Titration with controlled additions | High |
Using a dropper correctly
- Squeeze the bulb before placing the tip in the liquid.
- Immerse the tip and slowly release the bulb to draw liquid upwards.
- Hold the dropper vertically with the tip downwards, to avoid liquid running into the bulb.
- Squeeze gently to release one drop at a time.
- Rinse or discard the tip before using it with a different liquid.
Never allow liquid to enter the rubber bulb. Some solvents can swell or degrade the rubber, and residues can contaminate the next sample.
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Is a laboratory dropper the same as a pipette?
A dropper is a simple form of pipette, but it is not calibrated. Measuring pipettes are marked or calibrated for a specific volume.
Can a dropper be reused?
Glass droppers can be cleaned thoroughly and reused. Plastic droppers are often disposable. Use a clean one for each reagent to prevent contamination.
Why does liquid drip from the tip?
Warm air in the tube expands, or the liquid has low surface tension. Keep the dropper vertical and avoid holding the tube with your whole hand, which warms it.
Choosing droppers for your product
Laboratory droppers and the dropper pipettes used in product packaging are close relatives, but the packaging versions are fitted to the closure of a bottle. They combine a glass pipette, a teat and a collar on a DIN18 thread, and they are used for dispensing cosmetics, supplements and oils rather than for lab measurements. Graduated and laser-marked pipettes are available if you want visible marks for approximate dosing guidance on the label.
