How Accurate are Your Pipettes?
Your pipettes are probably most used tools in your lab and (I’ve said it before, but it’s worth repeating) without accurate pipetting you are asking for problems with your experiments.
Pipette manufacturers quote accuracy of pipettes but the truth is that pipetting accuracy is a very personal thing. It depends not only on the condition of your pipettes but also on your own pipetting technique.
It’s a very useful exercise to periodically measure your pipetting accuracy because this error is incorporated into every pipetting action you perform in the lab.
For most experiments the error might be too small to be significant but in some cases it might be very significant – e.g. if you are using a pipette to measure out a dilution for a very sensitive technique like HPLC.
The point is this: to know whether you pipette is accurate enough for the job you want it to do, you need to know the systematic error in your own pipetting.
It’s easy to measure your pipetting accuracy – just pipette the same volume of water ten times onto a tared balance, note the weight each time. Then measure the relative standard deviation in the dispensed masses by calculating the standard deviation and expressing it as a percentage of the average. This is your pipetting error.
Repeat this for several different volumes using each of your pipettes and you’ll get a pretty good idea of your overall pipetting accuracy that you can keep in mind when deciding whether your pipetting is accurate enough for the experiment you are doing.
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Accurate pipetting is not always an absolute essential; it depends on what you’re doing. Whilst it’s a good idea to look after your pipettes and aspirate as accurately as possible, most cloning procedures, for example, don’t require absolute accuracy and slight variation is fine. I say this because i come from a lab that calibrates their pipettes every 3 months, which given our role, is completely unnecessary and far too often. On the other hand, those preparing stock solutions for assays and the like, well then accurate pipetting is a must.
Nick, I didn’t think about that possibility. Thanks. Maybe you would, but do you think PIs would be willing to pay for those training? I guess depends on how much is the total cost, huh.
@Steve – I agree, this sort of thing is very frustrating. All we can do it try to educate! 🙂
@t-mac – I think having your pipettes calibrated is definitely worth it. It’s very difficult to do accurate and reproducible work when your basic tools don’t work accurately or reproducibly. If the agents you know of are too expensive, try shopping around or find out whether someone in your institute is trained to calibrate pipettes and could do it for you. Alternatively, it could be a good investment to find a course where you can be trained to properly calibrate your pipette yourself.
Hi. Do you think it is worthy to have one of many pipet calibrating agents to check your pipets? I feel like they charge somehow too expensive. Any idea other than asking them?
While I believe this sort of attention to detail is fundamental to quality research I’m not so sure other researchers feel the same way. If I had a nickel for every time I’ve seen someone drop their pipette over three feet onto a hard surface, pipette obvious bubbles, pipette sideways, or fail to understand how the final expulsion plunge on the pipette works I would be a very rich man. I wish it wasn’t this way in my lab and I do what I can to combat it, but in the end it’s futile.