Pipetting tips to improve accuracy and precision
Pipetting tips to improve accuracy and precision
Pipettes are routinely used in life sciences laboratories, yet some researchers still have inconsistencies in their liquid handling technique, even when following the same protocol every time. This can lead to poor data and reproducibility concerns, compromising the integrity of results. While quality assurance efforts in liquid handling typically place emphasis on pipette calibration, repair and maintenance, ensuring correct and consistent pipetting technique is just as critical for efficient workflows and successful projects.
At INTEGRA, our application team has decades of combined experience in liquid handling, so we have put together this video series to provide you and your laboratory colleagues with general rules, tips and tricks for correct pipetting. Following these simple guidelines will help to ensure:
- Accuracy and precision for every aspiration and dispense, further increasing the reproducibility and reliability of results
- Consistent operation of both manual and electronic micropipettes
- Improved pipetting of ‘problem liquids’ – such as viscous and volatile liquids
- Correct maintenance for long-term operation
What is accuracy and precision, and why are they important for pipetting?
Pipetting accuracy is how close the volume actually dispensed is to the set value, while precision covers how consistent the volume is over numerous dispenses. A well-maintained pipette provides confidence that you are working with a precise tool, but the accuracy of each dispense is determined by correct use of that tool, and the experience of the operator. This video covers the importance of both accuracy and precision in pipetting, to help you identify where you may be having difficulties in your own workflows, and how simple adjustments can improve results.
When should I use a manual or electronic pipette?
Manual or electronic? Manual pipettes can be fantastic tools for a few dispenses of individual samples, but the higher throughput and repeat dispense functionality offered by electronic pipettes can help to ease your workload. Electronic pipettes also offer better precision – because the action of the plunger is controlled by a motor – and a more ergonomic solution, requiring less physical effort and fewer aspiration/dispense cycles. This video helps you to make a more informed decision whether to use manual or electronic pipettes for each task in your workflow.
Should I use a pipette over the full volume range?
We always recommend working within 35 to 100 % volume range of any pipette. This is because the accuracy and precision decreases below 35 % of the maximum specified volume. However, this is only the tip of the iceberg! For more useful information and tips on pipetting volume, check out this video.
Why are my tips dripping?
After aspiration, the liquid in a pipette tip can begin to evaporate almost instantly, due to atmospheric differences between the tip, the liquid and the laboratory environment. This can lead to an increase in the air pressure inside the tip, which might result in liquid being forced out and dripping. This problem is most common when working with volatile liquids – such as ethanol, acetone, or chloroform – and the impact can be wide ranging, from a reduction in the precision and accuracy of pipetting to contamination of the workspace. This video covers simple solutions to this issue, such as how to properly pre-wet your pipette to equilibrate the air pressure and humidity in the tip.
How should I hold the pipette in order to pipette more accurately and precisely?
Pipette handling is a skill that is second nature to most researchers, but bad habits can reduce overall precision and accuracy. This can have a significant knock-on effect on results down the line.
Fortunately, improving your pipetting technique is something that is simple to do, and that can be implemented right away. For example, did you know that holding your pipette at the same angle as much as possible is important? Or that, for very low volumes of under 50 μl, the pipette should be held completely vertical?. All of this, along with real life demonstrations, can be found in this video.
Does it matter how deep my pipette is inserted in the liquid when I aspirate?
In short, yes it does. The immersion depth of the pipette tip is crucial, because the deeper it is submerged in the source liquid, the greater the chance of excess liquid sticking to the outside of the tip. This can result in aspirating slightly more liquid than intended, with detrimental impacts on your workflow and results, especially when pipetting very small volumes. Ideally, the tip should only be inserted 2-3 mm into the source liquid for aspiration, using the wall of your source vessel to help guide you. There are exceptions to this though, so watch this video to find out more.
After dispensing, there is a drop on my tip. What should I do with it?
There may be a drop of liquid on the end of the tip after dispensing. This is part of the target volume liquid, and must be added to the liquid already dispensed. This requires ‘tip touch’ or ‘touch off’ – but there are three options for how to perform it. Watch the video to learn which to use for your application.
How should I pipette very viscous liquids?
This can be one of the biggest pain points when it comes to pipetting in life sciences laboratories. Firstly, you need to pipette at a slower speed, and pause before finishing every aspiration or dispense. It is also a sensible idea to use a reverse pipetting technique – aspirating more liquid than you need, dispensing the desired amount, and discarding the small post-dispense volume as waste.
How should I pipette volatile liquids?
Pipetting volatile liquids also means you will have to alter your technique slightly to ensure you aren’t under-dispensing. This is because volatile liquids evaporate much faster, which can lead to dripping tips and the loss of liquid between aspiration and dispensing. The best way to combat this is to pre-wet your tip with the liquid you will be pipetting. This equilibrates the air pressure and humidity within the tip. It is also sensible to pipette faster after aspiration than you normally might – getting your liquid into the target vessel as quick as possible. Lastly, reverse pipetting can help as well. However, there are some exceptions to these rules, so watch this video to find out more!
Is there anything I can do to increase my accuracy and precision for repeat dispensing with an electronic pipette?
You should always discard the first and the last aliquot when repeat dispensing. This is because the mechanism inside the pipette needs to change from the aspiration to the dispense direction, potentially affecting the accuracy of the first dispense. Similarly, the final aliquot is an accumulation of all the dispense accuracy errors from the other aliquots, and may differ from the target volume. This video covers all of this, along with demonstrations.
How can I ensure that my pipette will perform as well as possible, for as long as possible?
Regular maintenance is the final key attribute in guaranteeing the highest degree of accuracy and precision for the lifespan of your pipette. Correct storage when not in use, combined with regular cleaning, leak testing and calibration, are all important. Watch this video for our handy guide covering all of these.
Has any of this been helpful? Do these challenges sound at all familiar to you? Download a poster of these tips and tricks to place in your laboratory!
Further reading: The complete guide to micropipettes