Liquid Pipetting Accuracy Is Influenced by Temperature

Thermal disequilibrium is a source of error prevalent in today's laboratories. Many assays and tests require the addition of liquids that are warmer or colder than the laboratory environment and the actual pipettes.

The extreme pipetting expedition is a multi-phase, year-long scientific study to investigate and illustrate the impact of laboratory conditions on data integrity. Yellowstone [U.S.] National Park (located in the U.S. states of Montana, Wyoming, and Idaho) was selected for Mission #2 of the expedition because it is emblematic of thermal variation and disequilibrium.

The aim of the extreme pipetting expedition is to raise awareness about common laboratory extremes that can affect data quality, including the thermal disequilibrium phenomenon. Restriction enzymes used in nucleic acid work, for example, are frequently handled at ice temperature (0°C), and higher temperatures are encountered when handling mammalian cell cultures (37°C) or polymerase chain reaction (PCR) solutions (60°C or higher).

The volume differences found in the study can be explained by the air displacement operation of pipettes. The dead air volume in pipettes acts to pull liquid into the pipette tip. When inserting the pipette tip into warm fluid, the air inside the tip is at ambient temperature. During aspiration, the pipette tip heats up, causing the air to expand and push liquid out of the tip. This causes less liquid to be dispensed, leading to variation between the target and delivered volumes. The opposite occurs when pipetting cold liquids.

Liquid volumes were measured using the Artel (Westbrook, ME, USA) pipette calibration system (PCS), a portable, robust measurement technology based on ratiometric photometry. Artel released the data from Mission #2 at the American Academy of Clinical Chemistry (AACC) Annual Meeting & Clinical Lab Expo, San Diego, (CA, USA) on July 17-19, 2007.

"From our testing at Yellowstone, it is clear that pipettes show a bias in volume delivery when dispensing fluids at different temperatures, and the error is especially significant when handling small liquid quantities,” says George Rodrigues, Ph.D., senior scientific manager at Artel and expedition leader. "Laboratories must account for this variation to ensure good accuracy and precision in test results.”


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