Forward pipetting is a commonly used method for dispensing aqueous solutions and blending samples into other liquids. To perform forward pipetting, you should fill the pipette to the first stop and then empty it by pushing the plunger to the second stop.
On the other hand, reverse pipetting is employed to introduce liquid into the upper fluid cell or to ensure accurate dispensing of viscous, volatile, and foaming liquids. To use this technique, you fill the pipette to the maximum extent, empty it by pushing the plunger to the first stop and then press the plunger to the second stop to return or discard the excess liquid. It is generally acknowledged that forward pipetting is more precise than reverse pipetting, especially for small volumes. However, reverse pipetting can be accurate for larger volumes if the proper technique is employed.
Here are some tips for effective pipetting:
- Use a calibrated pipette
- Use the smallest pipette possible
- Wipe the outside of the pipette tip before dispensing
- Change the pipette tip after each sample
- Maintain and calibrate your pipettes according to the manufacturer's instructions