My Pipettes Haven't Been Calibrated In Forever. Now What?
- Should I be concerned?
Yes, you should. If your pipettes have not been calibrated recently, the quality of your results and the integrity of your data are questionable. Especially when resources are scarce, labs must be able to depend on the quality of their liquid handling processes, and cannot afford to repeat their tests or experiments or waste their materials. Maintaining regulatory compliance is another good reason to have a robust pipette calibration system.
- Why would pipette performance change over time?
Pipettes are high-precision instruments, even though not many people think of them in that way. A number of moving parts within each pipette can fail during regular use or as a result of damage from incorrect use. Mechanical failures can include leaky seals and O-rings, damage to the nose cone of the shaft, corrosion and contamination of the piston— to name but a few.
- Should I be worried about my data?
For sure. The longer the time since your last pipette calibration or performance verification, the greater the threat to your data integrity. A rational step would be to do an “as found” performance check on each of your pipettes. If a pipette is not performing to specification, all data collected since your last calibration with the failed pipette are potentially flawed.
- Is remedial action required?
If your data integrity has been compromised, it is very likely that remedial action is required. Determine what regulations you are subject to and consult the relevant guidelines and SOPs. Of course, if any of your results are in doubt, you need to take action from not only a regulatory compliance standpoint, but also to ensure the enduring quality of your lab operations.
- Why did I allow so much time to elapse before I calibrated my pipettes?
Understanding how you got here is important in crafting an effective solution. Perhaps laboratory staff members find it burdensome to calibrate. Possibly your SOPs are not clearly documented and accountabilities are vague. Or, if you outsource calibration, you may simply be having difficulty with the price or performance of your provider. Whatever the case, you now should determine the ideal calibration program for your lab to ensure pipette quality.
- What options are available for calibration?
There are many options for pipette calibration and the right choice depends on the relative importance of accuracy, precision, traceability and the volume range of the pipettes. Gravimetry, fluorometry, titration, single-dye photometry, and ratiometric photometry are all techniques that can be utilized to calibrate your pipettes. Gravimetry, for example, offers good accuracy at high volumes but is problematic for low volumes and in difficult environments. Fluorometry and single-dye photometry provide good precision information but limited accuracy information. Titration is typically time consuming and the results are subjective. Ratiometric photometry offers high levels of precision and accuracy. If utilized as a system with prepared reagents, a high performance photometer and data management software, it can also provide fast and objective results at all volumes.
- How often should I calibrate?
The appropriate pipette calibration interval depends upon several factors including the degree of confidence required in your results, the amount and type of use a pipette receives, and the accuracy and precision required for specific procedures. In some cases, pipette performance should be verified daily. In other cases, monthly or quarterly is sufficient. One solution many labs have implemented is to partner with an outside provider for annual calibrations, while also utilizing an in-house program to perform interim verifications. An internal system—typically less rigorous than a full calibration and easy to implement—enables you to ensure the quality of your ongoing operations whenever necessary. For instance, you may want to verify pipette performance before critical procedures, or when you suspect a mechanical failure of the pipette.
Also important is your target reliability level, which is determined by the quality mandate and established tolerances in a given lab. Your quality assurance objectives and the appropriate regulatory standards should also be taken into consideration when deciding on calibration frequency. While all of this may sound complex, there is expert guidance available from sources such as LHTalk.org, and other web-based discussion groups.
- How do I prevent this situation from arising again?
You now need to implement a liquid handling quality assurance program. This should include the appropriate procedures, training, and a clear accountability structure for enforcement. With a good calibration program in place, you’ll have greater confidence in your data, prevent the erosion of lab efficiency, and rest assured your processes are compliant and in control.