Improving data quality and reproducibility (Part 3): temperature differences affect assay data quality
May 25, 2016
Can differences between sample and ambient temperatures affect the quality of your assay data?
In short, yes – and here is what is happening: When the temperature of a liquid sample is significantly different from the air temperature of the surrounding environment, pipetting accuracy and precision are affected. This phenomenon introduces variability to your assay data, but just how much inaccuracy should you expect and what can you do to minimize the resulting variability?
To bring attention to how environmental conditions affect data quality, a team of Artel scientists traveled to several extreme locations that mimic these conditions. In the article “The Effect of Fluid Temperature on Data Integrity”, Yellowstone National Park provides the setting for studying how the difference in temperature between a sample and the surrounding environment affects pipetting performance. We’ve summarized the findings below, and you can take a closer look at the test details and collected data by reading the full article.
It’s all about air
If you’ve read previous Digest posts about pipetting technique, or Artel Lab Report 2 , you’re familiar with the physics of the pipetting mechanism and how it can be affected by temperature. In short, the way the column of air inside the pipette tip behaves when it interacts with the liquid sample affects the accuracy, precision, and trueness of liquid handling, and it all stems from the Ideal Gas Law:
Affecting pipetting accuracy
Let’s start with a sample that’s warmer than room temperature. Before aspiration, the pipette tip is filled with air that’s at room temperature. Once the warm sample enters the pipette tip, the air inside the tip starts to heat up and expand, pushing liquid back out of the tip. Less liquid is aspirated and subsequently dispensed, leading to differences between the expected volume and the actual volume that is delivered.
The reverse is true for colder liquids. The air in the pipette tip cools down and the air volume shrinks, pulling more liquid into the tip. The net result is over-aspiration followed by over-delivery of liquid.
Affecting pipetting precision
With liquids that are colder or hotter than room temperature, it’s not just pipetting accuracy but also precision that can be affected. This is especially true if the same tip is reused for several aspirate and dispense cycles, or when operating in multi-dispense mode using an air displacement pipette. As the colder or hotter liquid in the tip equilibrates with the environmental temperature, the volume of the air in the pipette tip also changes, leading to variable volume delivery over time.
The situation is dynamic, i.e., depending on rates of heat transfer. Pipetting speed, type of sample container, and volume of captive air in the pipette tip all affect the speed of temperature change and will have a noticeable impact on the delivered volume.
Will this variability affect the quality of assay data?
Exactly how variability in pipette performance will affect the quality of your data depends on your particular assay and how critical the affected volume delivery step is to assay performance. In addition, the inaccuracy of your volume delivery will depend on protocol-specific factors, such as how much volume is being pipetted and the volume ranges of both the pipette and the pipette tip.
The effect can be considerable – in some situations, we’ve found as much as 37% inaccuracy in volume delivery.
So take a look at the full article “The Effect of Fluid Temperature on Data Integrity” to better understand the factors involved, and how your assay data may be affected. You’ll also learn 5 steps that can help minimize the risks associated with ambient and sample temperature differences.
- Blog: Pipetting in extreme environments: Science, adventure, art and the “Why”
- Lab Report: Impact of Pipetting Technique
- Publication: Best Practices for the Use of Micropipets
- Publication: Minimizing Liquid Delivery Risk: Pipettes as Sources of Error
About the Author
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.