A pipette is a volumetric instrument used to transfer small amounts of liquid. The liquid to be transferred is drawn into one end of a glass cylinder by squeezing the rubber ball at the opposite end or by sucking. The glass pipette is marked with white ceramic to allow the accurate transfer of the required volume.
Types of Pipettes
There are three types of volumetric pipettes: volumetric transfer, measuring, and serological. Because of volume gradations, the serological pipettes can dispense varying volume of liquids. While using the serological pipette, do not include the tip region in the volume measurements. These pipettes are graduated with white ceramic along their sides. Do not drain or blow out the measuring pipettes when delivering a solution because the extra volume in the tip is not part of the pipette’s calculated volume. The volumetric pipettes are designed to dispense one specified volume of liquid, whereas the measuring pipette is calibrated to dispense different volumes. Unlike the serological pipette, both of these pipettes are designed to include the tip region in their entire dispensed volumes.
To fill a measuring or serological pipette follow the following method:
- Draw the solution to be transferred just above the volumetric level, then let the solution fall to the calibration mark.
- Remove the pipette from where the fluid is drawn, and wipe the tip with a laboratory tissue to remove any excess solution drops from the outside of the pipette.
- When dispensing the fluid from a measuring pipette, let the tip touch the side of the receiving container and let the fluid flow. If one is dispensing the liquid by hand, control the flow rate by placing the thumb on the end of the pipette. However, never let the thumb wander away from the end of the pipette because it will let the fluid flow uncontrollably.
- Thoroughly drain the solution from the pipette.
- Do not remove the tip with an upward or downward motion.