Pumps, Valves & Liquid Handling
Are you using the right micropipette? Lukas Keller, PhD, Marketing Communications Director, Integra Biosciences
Lab professionals can spend numerous hours a day with a micropipette in their hand, and it is often a challenge to improve pipetting effi ciency and guarantee reliable results. Selecting the right micropipette for any given application is key to the success of lab work; not only does it ensure the performance of any experiments, but it can also boost effi ciency. Understanding the needs of a pipetting workfl ow allows users to select pipettes that are accurate and reproducible, but there are a number of other factors that should be considered to improve pipetting results and guarantee the success of an experiment.
Physical properties of the liquid
Broadly speaking, there are three main categories of liquids: aqueous, viscous and volatile. Most liquids are of the aqueous type, making air displacement pipettes the fi rst choice for many. Although the majority of liquids will work perfectly well using this pipette type, positive displacement pipettes should be chosen used when working with very viscous or volatile liquids. The differences between these pipette types are shown in Figure 1. It is also essential that the correct pipetting technique is used – regardless of the liquid type – to achieve excellent results.
Figure 1
Figure 2
And it’s not just the pipette that needs to be considered. Pipette tips can cause all manner of problems if they loosen, leak or fall off. This common issue in laboratories is normally caused by the use of universal pipette tips, as such tips frequently require ‘hammering on’. This process stretches the pipette tip rim, and can lead to leaking or misalignment of tips, or even cause them to fall off the pipette completely. Choosing high quality micropipettes that were designed together with specifi c tips ensures a more secure connection, offering much higher levels of reliability and better results. In addition, something as simple as colour coding pipettes and tips also helps users to make sure that they choose the right tips for their pipette.
Accuracy and precision
Two of the most critical parameters affecting pipetting results are accuracy and precision (Figure 2).
There are several criteria that should be kept in mind in order to achieve maximum pipetting accuracy, precision and reliability. As a rule of thumb, users should always choose the smallest pipette capable of handling the required transfer volume. This is important, because accuracy decreases when the set volume is close to the pipette’s minimum capacity. For example, if you dispense 50 µl using a 5,000 µl pipette, results may be poor. Using a 300 µl pipette will give you far better results, while a 50 µl pipette offers the best results. Additionally, volumes set on traditional manual pipettes can change while pipetting, due to unintentional plunger turns. This is why some pipette manufacturers have developed locking volume adjustment designs, preventing inadvertent changes while pipetting to further ensure accuracy. Calibration is another important aspect, helping to safeguard reliable results by certifying a pipette’s accuracy and precision. The process should be easy for users; for instance, some electronic pipettes can set a calibration reminder, or save the calibration history.
Effi ciency
In a high throughput setting, it is important to be as effi cient as possible while keeping pipetting processes reliable and consistent. There are many ways to improve pipetting effi ciency, including the use of multichannel and/or electronic pipettes. These versatile instruments usually offer multiple different pipetting modes – such as reverse pipetting, variable dispensing, programmed serial dilutions and many more – streamlining processes. For example, programs such as repeat dispensing are perfect for dispensing multiple aliquots of the same volume, without having to refi ll the tips.
Transferring samples between labware of different formats can quickly become very tedious and error prone using single channel pipettes. Multichannel pipettes allow the transfer of multiple samples at once, in the blink of an eye. This not only improves effi ciency, but also helps to prevent pipetting errors and repetitive strain injuries (RSIs). Some pipettes are even able to change tip spacing during pipetting, allowing parallel transfer of multiple samples between different labware sizes and formats, which can save hours of time (Figure 3).
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