At Death Valley for mission No. 3 of the Extreme Pipetting Expedition, Artel, Westbrook, Me, found that pipettes under-deliver by up to 35% in dry and hot environments. While volume-delivery errors were partially reduced by prewetting pipette tips, under-delivery still persisted, and the pipettes were found to operate out of specification in most instances.
Lab technicians often encounter dry heat in their work environments, which can affect pipette performance and compromise assay results. Labs using analytical instruments, ovens, incubators, freezers, and other devices requiring high power or open flames are prone to heat and low humidity. Heating and air-conditioning systems not equipped with humidifiers may also contribute to dry heat, and to ensure pipetting accuracy and precision and strengthen data integrity, it is useful for lab scientists to understand and compensate for this source of error.
The expedition is a multi-phase, yearlong scientific study to illustrate the impact of lab environmental conditions on pipetting performance and data integrity.
As in previous missions, error caused by the environmental conditions at Death Valley was greater when pipettes were set to their minimum volumes than when they were set to their maximum volumes. A 2-microliter pipette set to deliver its minimum volume of 0.2 microliter without pre-wetting under-delivered by 34.7%. Pre-wetting reduced the error to 30.9%, but the pipette was still operating outside its minimum-volume accuracy specification of 12%. When set to its maximum volume of two microliters without pre-wetting, the pipette under-delivered by 7% without pre-wetting and by 4.8% with pre-wetting, both outside of the manufacturer’s accuracy specification.
When working with larger liquid volumes, errors were also induced by the hot and dry conditions, but on a smaller magnitude. Without pre-wetting, a 20-microliter pipette at its minimum volume under-delivered by 16.8%, which is a lower inaccuracy than exhibited by a non-pre-wet 2-microliter pipette at its minimum volume (34.7% error). Pre-wetting the 20-microliter pipette prior to dispensing its minimum volume of two microliters reduced error to 7.4%.
Humidity and temperature can vary across labs in different regions, between labs on different floors, and within areas in labs.
Liquid-handling error experienced in dry heat is largely due to evaporation. The evaporation of a miniscule amount of liquid inside the pipette tip showed a large effect on pipetted volumes, especially when target volumes were in the microliter range. When one microliter of liquid evaporates, it converts into more than 1,000 microliters of gas, expanding by a factor of 1,250 to 1,450, depending on temperature. The expansion prevents the pipette from aspirating the desired target volume.
A 3.3-million-acre desert, Death Valley was picked for the mission because of its iconic hot and dry climate. Surrounded by mountains, the valley captures and retains extreme amounts of heat to create one of the hottest environments on earth, commonly exceeding 49oC (120oF). Death Valley is also the driest locale in the United States, receiving fewer than two inches of rain annually.
Previous missions explored how barometric pressure and pipetting warm and cold liquids affect data integrity.
The company planned to release the results at the Association for Molecular Pathology (AMP) 2007 annual meeting Nov 7-10 at the Hyatt Regency Century Plaza Hotel in Los Angeles. For more information, visit [removed]www.artel-usa.com/extreme[/removed].