Definition
A graduated pipette is a laboratory glass or plastic instrument used to measure and transfer variable volumes of liquid. It features a series of calibrated markings (graduations) along its length that allow the user to dispense a selected amount of fluid with a reasonable degree of precision.
Overview
Graduated pipettes are commonly employed in analytical chemistry, biology, and other scientific disciplines for tasks such as titration, solution preparation, and sample handling. Unlike fixed‑volume (volumetric) pipettes, which deliver a single, highly accurate volume, graduated pipettes permit the user to select any volume within the instrument’s range, typically from a few milliliters up to 100 mL, depending on the model. Two principal designs are recognized:
- Mohr pipette – a graduated pipette that terminates before the tip, requiring the user to discard the final drop to achieve a “to deliver” (TD) measurement.
- Serological pipette – a graduated pipette whose scale extends to the tip, allowing the last drop to be included in the delivered volume (also TD, but calibrated differently).
Graduated pipettes are calibrated for use at a standard temperature of 20 °C (68 °F) and are usually made of borosilicate glass due to its chemical resistance and thermal stability; disposable plastic versions are also available for low‑risk or contamination‑sensitive applications.
Etymology/Origin
Pipette derives from the French word pipette, a diminutive of pipe (itself from Latin pīpa, meaning “a pipe or tube”). The adjective graduated originates from the Latin gradus meaning “step” or “degree,” referring to the incremental markings along the instrument’s length.
Characteristics
| Feature | Typical Details |
|---|---|
| Material | Borosilicate glass (e.g., Pyrex) or disposable polypropylene/plastic |
| Capacity range | 1 mL – 100 mL (common sizes: 5 mL, 10 mL, 25 mL, 50 mL) |
| Calibration type | To deliver (TD) – calibrated to dispense the indicated volume; some are to contain (TC). |
| Markings | Linear or non‑linear (e.g., for specific analytical methods); engraved or printed. |
| Accuracy | Typically ±0.5 % to ±1 % of the indicated volume, depending on size and quality. |
| Usage procedure | 1. Rinse with the solution to be transferred. 2. Fill above the desired graduation. 3. Adjust the liquid level to the required mark (Mohr) or dispense until the meniscus reaches the mark (Serological). |
| Cleaning & maintenance | Glass pipettes are washed with detergent, rinsed with distilled water, and dried; plastic pipettes are generally single‑use. |
Related Topics
- Volumetric pipette – a fixed‑volume pipette calibrated for a single, highly accurate volume.
- Micropipette – a precision instrument for dispensing volumes in the microliter range, often using disposable tips.
- Burette – a graduated glass tube with a stopcock, used for delivering variable volumes in titration.
- Serological pipette – a type of graduated pipette that includes graduations up to the tip.
- Mohr pipette – a graduated pipette that stops short of the tip, requiring discard of the final drop.
- Analytical balance – a high‑precision weighing device often paired with volumetric equipment for quantitative analysis.
This entry reflects information compiled from standard laboratory equipment references and peer‑reviewed analytical chemistry texts.