The Effects of Hot and Dry Conditions
on Pipette Performance

The use of air-displacement pipettes in conditions of low humidity and high temperatures induced consistent inaccuracies on the volumes of delivered aqueous solutions.

Without pre-wetting the pipette tips prior to aspirating and dispensing the sample, data acquired in Death Valley National park at 7% relative humidity and 44°C showed consistent under-delivery of the samples. These delivery errors were incurred regardless of the pipette brand or its set volume, as shown in Figure 1. Twenty of the twenty-two volume settings exceeded the manufacturers’ specifications, as denoted by the red asterisks in the graph.

When sample solution was aspirated and dispensed five times prior to delivery into the cuvette of the PCS® instrument, the inaccuracies were reduced consistently, as shown in Figure 2. While pre-wetting the tips reduced the magnitude of the errors, it did not completely compensate for the extremely dry and hot conditions encountered in Death Valley. Several pipettes now dispensed volumes, which met the manufacturers’ specifications for that particular set volume. Even at set volumes, at which the specifications were not met, the error was consistently reduced by pre-wetting the tips.

The magnitude of errors observed in both studies demonstrates clearly that small volumes are more susceptible to the influence of humidity and temperature than larger volumes. Additionally, inaccuracies were found to be significantly smaller when pipettes are used at their nominal volume, than at or close to their smallest recommended volume. This fact has also been observed in previous studies investigating the effects of thermal disequilibria and changes in barometric pressure.

CONCLUSIONS

Many technicians and scientists have limited control over the room temperature and humidity settings in their laboratory. In many laboratories, these parameters are determined or affected by the geographic location of the laboratory, the type of laboratory, and the equipment used therein. Significant influence on the relative humidity is exerted also by the heating and air conditioning systems with which the laboratory is equipped.

While most laboratories do not operate under conditions as extreme as experienced in Death Valley, it is not uncommon to encounter extremely low humidity levels (particularly during the winter heating season), or significantly elevated temperatures where many high-powered instruments or heating equipment are used, or even gas burners, as in many microbiology labs. Oftentimes, environmental conditions can vary significantly between rooms on the same floor in the same building.

It is common practice to develop experiments in one location, and then transfer the protocol to another laboratory for routine use. Sometimes the new laboratory is situated just across the hallway, other times it may be located in a different part of the country, or even on a different continent.

Regardless of where experiments have been developed and where they are eventually being conducted; when comparing results, it is imperative to keep these potential sources of error in mind, in addition to the “usual suspects” — sample and reagent quality, instrument error, operator error, and flawed protocol, to name but a few.

Reliability and trust in the obtained results begins with the delivery of accurate volumes!