ARTEL Study Shows that Pipetting Warm and Cold Liquids Causes Error of up to 37 Percent
News Jul 17, 2007
Data taken at Yellowstone National Park during Mission #2 of the ARTEL Extreme Pipetting Expedition show that pipettes deliver volumes inaccurate by up to 37 percent when handling fluids at temperatures different from the pipettes.
Called thermal disequilibrium, this source of error is prevalent in today’s laboratories, as many assays and tests require the addition of liquids which are warmer or colder than the laboratory environment and the actual pipettes.
Yellowstone was selected for Mission #2 of the Expedition because it is emblematic of thermal variation and disequilibrium. The Extreme Pipetting Expedition is a multi-phase, year-long scientific study to investigate and illustrate the impact of laboratory conditions on data integrity.
ARTEL is releasing the results from Mission #2 of the Extreme Pipetting Expedition at the 2007 AACC Annual Meeting & Clinical Lab Expo, San Diego, CA, July 17-19, Booth #4143. The data will also be published at www.artel-usa.com/extreme.
“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.”
Data taken at Yellowstone show that error caused by thermal disequilibrium was significant when using smaller volume pipettes at their minimum volumes. For example, a two-microliter variable-volume pipette set to deliver 0.2 microliters over-delivered cold liquid (3oC) by 37 percent and under-delivered warm liquid (45oC) by 24 percent, compared with liquid at room temperature (21oC). When set to deliver its maximum volume (two microliters), the pipette over-delivered cold liquid by one percent and under-delivered warm liquid by seven percent.
As expected, error was present, but smaller, when working with larger liquid volumes. The 20-microliter pipette set to deliver two microliters over-delivered cold liquid by four percent. When the pipette was set to deliver its maximum volume of 20 microliters, the overdelivery amounted to 0.6 percent.
“There are not many laboratory managers who would knowingly accept error of more than a few percent, let alone error of 37 percent,” says Doreen Rumery, Quality Control Manager at ARTEL and Extreme Pipetting Expedition member. “Yet many technicians frequently pipette warm and cold liquids in critical testing and assay work without accounting for volume variation.”
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.
“Since the magnitude of error is dependent on a number of protocol-specific details, such as pipetting speed and type of sample container, a one-size-fits-all correction factor does not currently exist,” says Rodrigues. “ARTEL will continue to study thermal disequilibrium to help laboratories develop strategies to minimize this source of laboratory error.”
Volumes were measured using the ARTEL PCS® (Pipette Calibration System), a portable measurement technology based on ratiometric photometry.