A volumetric pipette – also known as a bulb pipette or belly pipette – is designed for high-precision measurement of liquid volumes, typically accurate to four significant figures. Each pipette is calibrated to deliver one fixed, exact volume of liquid.
These pipettes feature a large central bulb with a long, narrow stem above it and a single calibration mark, similar in concept to a volumetric flask. Common capacities include 1, 2, 5, 10, 20, 25, 50, and 100 mL. They are widely used in analytical chemistry, especially for preparing solutions from stock reagents and for titration procedures.
Accuracy and Standards
The ASTM E969 standard defines accuracy tolerances for volumetric transfer pipettes. Accuracy varies by capacity. For example:
- 0.5 mL pipette: tolerance of ±0.006 mL
- 50 mL pipette: tolerance of ±0.05 mL
These values apply to Class A pipettes; Class B pipettes allow approximately double the tolerance.
Specialized Variant
A specialized version is the microfluid pipette, capable of dispensing very small volumes – down to about 10 μL – using a circulating-liquid tip that produces a self-confining droplet at the outlet.
History
Pyrex began producing laboratory glassware in 1916 and quickly became a preferred material for scientific work due to its borosilicate composition, which offers exceptional resistance to chemicals, thermal fluctuations, and mechanical stress.
