Factors Affecting Pipette Accuracy

Quick links

• Forward, Reverse, Repetitive, & Heterogeneous Sample Pipetting
• Pipetting Recommendations for Different Sample Types
• 10 Steps to Improve Pipetting Accuracy
• Pipette Accuracy vs. Precision
• Preventing Cross Contamination

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Temperature

Temperature has many effects on pipetting accuracy. The factor that has the greatest effect is the temperature difference between the delivery device and the liquid. The air gap (dead air volume) between the liquid surface and the piston experiences thermal expansion effects unique to the case. This either reduces or increases the liquid amount aspirated into the tip, along with other effects.

Density

The density (mass/volume ratio) affects the liquid volume that is aspirated into the tip. A smaller dose of liquid with higher density than water is aspirated compared to a similar operation with water. With lower density liquids the effect is the opposite. This is caused by the flexible dead air volume along with earth’s gravity. The density of liquids also varies according to temperature. Typically the density of liquids also varies according to temperature. Typically the density for water is 0.998 kg/dm3, for ethanol 0.79 kg/dm3, and for sulfuric acid (95–98% h₂SO₄) 1.84 kg/dm3 (the values apply at the temperature of 20 °C/68 °F).

Altitude

Geographic altitude affects accuracy through air pressure. Air pressure decreases in higher altitudes, and the conversion factor Z decreases as well. Also, with some liquids, the boiling point decreases quite close to room temperature, which will increase the evaporation loss dramatically.