Pipetting Techniques - Getting the Best Results
Adopting good pipetting techniques is critical for the accuracy of your analysis.
"...a small mistake in pipetting can cause a large error in the final result. It is, therefore, of great importance to evaluate and to reduce, wherever possible, both random and systematic errors in liquid sample handling." Sari Ylätupa, PhD, "Choosing a Pipetting Technique Affects the Results of Your Analysis", European Clinical Laboratory
As with many forms of instrumentation, a pipette will only perform as well as the operator’s technique allows.
Despite the quality of the instrument and its calibration status variations in technique can alter delivery volumes.
What to consider to eliminate sources of pipetting error:
- The operating button should be pushed/released back slowly and steadily at all the times. Always control the push button movements with the thumb for consistency.
Take extra care while working with liquids of high viscosity (or use a positive displacement pipette). Never let the operating button snap back to the ready position while aspirating the liquid.
- Aspirate liquid into the pipette only when a proper tip is attached to its tip-holder.
- Always clean the tip holderwith a dry tissue paper before fixing the tip.
- Ensure that the tip is tightly fitted to the tip holder.
- Reject the tip if any liquid remains sticking on the inner wall of the tip even after the plunger is pushed to the second stage of pushbutton.
- While pipetting , the pipettor should be vertically straight and tip should be dipped only a few millimeters into the liquid.
- Allow liquids, Tips and Pipette to equilibrate with the ambient temperature.
- Pre-rinse the tip several times before use when pipetting at temperature different from ambient.
- Wipe the tip only if there is liquid on the outside of the tip, being careful to avoid touching the tip’s orifice.
- Don’t keep pipette in your hand while not working to avoid transferring of body heat to pipette.
- Select the correct pipetting technique(e.g, Reverse, forward etc.) depending on the nature of the liquid.
- Using excessive force to turn the push button outside the range specified for it may jam the mechanism and damage the pipettor.
- Regularly check pipettes for signs of wear., particularly on seals or o rings which can result in leaking. Damage to tip holders can affect air tightness and tip fit. Corrosion of pistons can affect calibration. Contacat firstname.lastname@example.org for further advice.
- Re-calibration is recommended every 6 months for a pipette used on daily basis. Re-calibration is also recommended in the following cases
When working with detergents or foaming liquids.
When working with high viscosity liquids.
In the event of dismantling of the pipette for servicing, greasing, O-ring replacement etc. www.pipetteservice.co.uk
- When not in use the pipettor should be rested upright on the pipette stand in the vertical position with the tip cone pointing downwards to prevent liquids entering the inside of the pipettor.
- Use disposable tips only once to avoid cross-contamination.
- Avoid using inferior quality tips to ensure accurate dispensing of the liquids.
Techniques among pipette users vary with background, personal preferences, and training. These differences in execution can affect the accuracy and/or the precision of results being released from the clinical or research lab. To ensure accuracy and consistency, facilities should adopt standard operating procedures for pipetting techniques and ensure that all operators are trained to an adequate level of proficiency. By increasing the level of consistency in results obtained, the level of quality and credibility of the facility will be enhanced.
1.Ylätupa Dr. S. "Choosing a Pipetting Technique Affects the Results of Your Analysis", Euopean Clinical Laboratory 1996. 10:14.