The volume delivered by a Class B pipette can vary with changes in temperature due to thermal expansion of the liquid and the pipette material. At higher temperatures, such as 27°C or 30°C, the liquid expands, which can increase its volume slightly.
If the pipette is calibrated at 20°C, using it at a higher temperature without accounting for this expansion could result in delivering a volume that is slightly greater than the nominal volume specified (between 24.94 ml and 25.06 ml).
Additionally, if the bulb or other parts of the pipette are held in the palm, the warmth from the hand can cause local heating, further increasing the volume of the liquid or affecting the pipette's material properties (e.g., causing it to expand). This temperature variation can affect the precision and accuracy of the delivered volume.
Therefore, the limits for the amount delivered by the pipette at 27°C or 30°C may shift, typically leading to a higher volume than those delivered at 20°C.