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Tech Focus : Apr 15, 2008 ( )
Quantifying Pipette Variability due to Humidity
Artel Investigators Examine the Effects of Extreme Humidity on Accuracy and Precision
Laboratory error can arise from a number of sources ranging from instrumentation malfunction to sample contamination and even operator error. The quality of laboratory data is dependent on the accuracy of the tools that are used to generate that information.
This article will discuss Mission #4, which visited the rainforest of Olympic National Park in Washington to test how humidity affects pipetted volumes. Understanding how pipettes perform in high humidity is critical for laboratory data integrity, because humidity levels can vary across laboratories and even within a laboratory itself.
According to regulatory standards, pipette calibration laboratories must keep their relative humidity at greater than 50%. Working laboratories are often significantly drier, though. By visiting Olympic National Park, Artel sought to determine how pipettes behave in a humid environment and whether varying humidity levels affect pipetting accuracy and precision.
Tools and Technique
The team conducted four experiments and in each, used a number of variable-volume pipettes from leading manufacturers that dispense a maximum of 1,000, 200, 20, and 2 µL. During the experiment, each pipette was used to dispense 10 data points, each at its maximum and minimum volumes.
Understanding the Effect
In an environment such as the Olympic National Park, both temperature and humidity must be evaluated to truly understand resulting volume variability.
In dry environments, evaporation occurs within pipette tips, leading to underdelivery of aqueous solutions. In an environment with constant relative humidity, greater evaporation occurs the warmer an environment is. The rate of evaporation is proportional to the evaporation potential, which is the difference between the partial pressure of water in air at saturation conditions and the actual partial pressure of water in air at ambient conditions. Understanding an environment’s evaporation potential is the first step in studying how humid conditions affect pipetted volumes.
To mimic pipette calibration laboratory conditions of 60% relative humidity and 20°C, Mission #4 was set for late September. In the morning of the first testing day, the humidity in the rainforest was above 60%, but the temperature was only 14°C. To understand pipette performance in the required temperature, the Artel team tested pipettes indoors at a hotel near the park. Pipettes performed accurately and precisely in this environment (Figures 1 and 2).
The next day, the team made its way to La Push First Beach, one of the beaches in Olympic National Park. Due to generator malfunctions, however, they were unable to run testing equipment. After finding a makeshift solution—a car battery—the team set up the equipment in the park at Rialto Beach. At 14°C and 74% relative humidity, the site had a very low evaporation potential, and the pipettes performed well (Figures 1 and 2).
Comparing and Correcting
Although pipettes demonstrated superb performance at Olympic National Park, most laboratories do not have similar environmental conditions. Except for pipette calibration facilities, laboratories typically operate at 15–40% relative humidity.
Doreen Rumery is lab technical manager and QC manager at Artel. Web: www.artel-usa.com. E-mail: firstname.lastname@example.org.
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