What are the effects of liquid temperature?

Answer

Liquid temperature can affect volume accuracy up to 37%. Temperature changes the fluid dynamics and other physical characteristics of fluids in different ways. Generally, lower temperatures increase viscosity and surface tension while decreasing vapour pressure. The opposite is true with hot liquids. The flow rate should be slower with colder liquids.

The difference between the ambient temperature and the liquid temperature also has an effect. When the aspirated liquid is cooler than the ambient air, the dead air volume will be cooled on contact. The temperature drop causes the dead air pressure to increase and the air volume to shrink. This means a slightly greater volume of liquid is drawn into the pipette, resulting in a greater volume being dispensed at the target. The opposite is true for a liquid hotter than the ambient.

In general, cold liquids over-deliver where hot liquids under-deliver. The degree of error is affected by many other factors relating to the liquid temperature.

• The greater the difference in temperature between the liquid and the ambient environment, the greater the degree of error.
• Larger dead air volumes exacerbate the liquid volume error by increasing the difference the air pressure has on the dead air volume.
• Smaller dispense volumes also experience more accuracy error. As the liquid temperature fluctuates the fluid dynamics change, like the viscosity, so the flow rate may no longer be suitable.
• The sample labware can affect the error. The material the labware is made out of and the volume it holds can affect how quickly the liquid temperature adjusts to the ambient temperature.

The best advice is to allow the liquid to equilibrate to the ambient temperature where possible. Reduce the dead air volume either through larger liquid volumes or smaller tips.

Finally, if you really want to be more accurate with an extreme temperature (not recommended), it’s possible to calculate the exact degree of error caused by the extreme temperature and simply correct the volume transferred. However, this is very specific to the protocol, pipette module, volume etc. This is extremely time-consuming to calculate and only for the truly determined, it should be considered a last resort.

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