Product Survey: Manual Micropipettes
It’s all about Ergonomics
by Harald Zähringer, Labtimes 01/2013
A good deal of daily laboratory work is still done by hand using manual micropipettes.
Micropipettes are essentially simple instruments made of only a few components that function according to a very basic concept. A piston inside a cylinder is pushed down by a hand-driven plunger and is forced to move in the opposite direction by a piston spring when the plunger is released. Liquids are aspirated into the pipette tips when the piston moves upwards and dispensed when it goes down. The volume is set by a screw that controls the length of the piston movements. Standard laboratory micropipettes work as air displacement pipettes. An air cushion between piston and the aspired liquid prevents the contact of the liquids with mechanical parts of the pipette. This fundamental design hasn’t changed since the invention of the micropipette by the German physician Heinrich Schnitger in 1957 and the further development of the first adjustable micropipette by Warren Gilson and Henry Lardy in the early seventies.
Micropipettes are, however, also extremely elaborate devices that have been brought to almost perfection by engineers and designers to attain the highest possible accuracy and precision. Pipette users may expect systematic errors (accuracy) as low as 0.5 to one percent if the instruments are operated at the maximum volumes and random errors (precision) between 0.2 and 0.7 percent. The differences in accuracy and precision between miscellaneous pipette brands are marginal and it should be taken for granted that modern state-of-the-art micropipettes work accurately and precisely.Stress for the thumb
Hence, pipette vendors focus on ergonomics to distinguish from competitors. The most obvious physical properties that have a significant impact on micropipette ergonomics are weight, plunger, blow-out and tip-ejection forces. The weight of a typical 200 µl single channel micropipette ranges between 70 and 110 grammes, except for VistaLabs Ovation pipette model that comes with a novel design and a considerably high weight of 160 grammes. A lighter pipette may reduce the stress on the muscles involved in holding the pipette. Some users, however, do not bother too much about the weight and even prefer the feel of a slightly heavier model.
The most important feature concerning ergonomics, however, is plunger, blow-out, and tip-ejection forces, which determine the workload on the thumb. Plunger forces are very similar throughout different pipette brands and range from around 0.4 to 0.7 kilogram-force (kgf). Much bigger differences are found for blow-out and tip-ejection forces. The latter may be as low as 0.4 kgf for VistaLab’s Ovation and as high as 4 kgf for Gilson’s Neo. That’s a remarkably wide span. So, why are classical Gilson pipettes, which are notoriously known for high blow-out and tip-ejection forces, still very popular amongst many life scientists? The answer is simple: whether a pipette has the right feel, grip or ergonomics, in the hand of an individual user is a very subjective decision and may even depend on emotional factors.
David Rempel’s ergonomics group at the University of California, evaluated the usability and ergonomics of five popular pipettes (Biohit mLine, Eppendorf Research, Gilson Neo, Rainin Pipet-Lite and VistaLab Ovation) based not only on objective measurements, such as tip-ejection forces, but also on usability ratings (Lichty et al., Work 39 (2011), 177-85).
According to objective data, VistaLabs Ovation having the lowest plunger, blow-out and tip-ejection forces should outperform all other pipettes. Lichty et al., however, report that the test users (21 participants with longstanding pipetting experience) struggled with the volume adjustment on the Ovation, which led to a significant downgrade in the cumulative usability rating. Interestingly, the test users attested at least one positive feature to each pipette model. However, and that’s the bottom line of Lichty et al.’s study, “None of these pipettes emerged as a clear, universal best choice for every user.” In other words: the only way to find a model that suits best individual ergonomic needs is by trying out and comparing as many pipettes as possible.
First published in Labtimes 01/2013. We give no guarantee and assume no liability for article and PDF-download.
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