Beyond Pipette Calibration: Setting Tolerance Limits

Setting Tolerance Limits

Are your pipettes performing well?

Setting Tolerance LimitsThis sounds like a simple yes or no question but, like many things, the reality is more nuanced. Here’s an example of what I mean:

A few years back I received a call from a lab that had just received a batch of brand new pipettes (handheld). They had been testing the pipettes’ performance and were dismayed to find that the pipettes didn’t perform to the manufacturer’s specifications. This lab had invested a lot of time into adjusting and re-testing their pipettes but they were unable to deliver volumes with the accuracy and precision stated by the pipette-maker. They reached out to us to see if we had any insights, and after some digging around and further conversations with the lab we were able to determine that, despite not meeting manufacturer’s specs, the pipettes were performing just fine, thank-you-very-much.

How could this be? It turns out that for the assays and types of liquid dispensing this lab was doing, the manufacturer’s specifications were too stringent. After careful examination of the work being done by this lab, we were able to develop a set of performance specifications and tolerance limits that kept the lab’s studies reliable and reproducible, and were achievable by the new pipettes.

Here are a few of the key insights that we shared with that lab, and that are generally applicable:

1. Manufacturers don’t test every single pipette

Like many manufacturers, most pipette makers don’t verify the performance of every pipette they make but rather sample a fraction of each lot. This usually works very well, but every once in a while some pipettes can go through that don’t really meet specifications. For this reason, we recommend that labs test the performance of all new pipettes.

2. Pipette performance depends on environment

Another reason your pipettes may not quite meet manufacturers’ stated specifications could be due to environment. Humidity and temperature can affect pipette performance,1 and very likely the manufacturers’ test environments differ from your working lab.  So, to best understand and manage your pipettes’ performance (and in comparing their actual performance to manufacturers’ specs) make sure to test your pipettes in the lab(s) where they will be used.

3. Manufacturer’s specifications may not be right for your lab

It turns out that there are no consistent standards for how manufacturers set performance claims. In addition, it’s possible that the manufacturer’s specifications are more stringent than your lab really needs. Before investing time in trying to meet manufacturer’s specifications, it’s worth taking a moment to review the assays, and the liquid dispensing needs for your lab, and developing the acceptable and achievable tolerance limits.

Calibration is just a start—develop a pipette performance plan that works for your lab

The lab I mentioned in the example above started well by checking the performance of their new pipettes before putting them into service, and then ran into a slight roadblock.  By not having a pipette performance plan in place that took into account the work that they did, they were unable to meet manufacturers’ tolerances. Which is not surprising—it’s human nature not to think about problems until they are, well, problems. And unless your pipettes are really not performing well or you work in a tightly regulated environment, you might not think very much about how much accuracy and precision you really need in a pipette. But developing a plan for pipette performance including tolerance limits can go a long way to balancing time and effort with reproducibility and experimental excellence. So take a few hours and set up a pipette performance plan that’s appropriate for your lab. You can learn how in Artel’s Lab Report 5: Setting Tolerances for Pipettes in the Laboratory.

Additional Resources


1. Piston-Operated Volumetric Apparatus—Part 2: Piston Pipettes. ISO 8655-2:2002.

About the Author

Doreen Rumery

Doreen Rumery, Laboratory Technical Manager and Quality Control Manager at Artel, is a certified Medical Laboratory Technologist and ASQ Certified Manager of Quality/Organizational Excellence with more than 30 years in the clinical laboratory and manufacturing industries.  Doreen oversees all laboratory activities at Artel, including technical operations, method validation, technician training and conformance with current regulatory standards.

Download Lab Report 5: Setting Tolerances for Pipettes in the Laboratory