Pipettes are the most essential and most frequently used tools in any clinical or research laboratory. So take your time to choose an ergonomic model that meets your needs.

Usually manual pipetting involves five steps: depressing the pipette’s plunger, holding the plunger down, aspiring the liquid, dispensing it and expelling it. After the last step the tip is ejected and a new one applied. Pretty mundane stuff I hear you say, but have you ever wondered how often your thumb depresses the plunger or tip ejector and how much cumulative force is used in carrying out a normal day’s lab work? The plunger force of a traditional manual pipette is equivalent to between three and four kilograms. This means that if you press the plunger, say, 150 times a day, your thumb has to move a total mass of nearly half a ton.

Tingling hands

Small wonder that many pipette users complain of thumb pain or experience tingling in their hands, fingers and shoulders. According to a study published in 1994 by Marianne G. Bjornsten and collegues from the University Hospital in Uppsala, Sweden, lab workers who wield their pipettes for more than six hours a week attract a significantly higher risk of repetitive strain injuries. Indeed, an astonishingly high risk of strain and muscle injuries is associated with heavy pipetting. One of the most well known hazards is carpal tunnel syndrome, which causes severe pain in the hand and fingers, especially the thumb.

Health problems can be avoided by choosing pipettes not only according to their precision and accuracy but also by taking a closer look at their ergonomics. The plunger force of modern ergonomic manual pipettes is much lower than that of traditional pipettes. Usually it does not exceed 0.5 to 1 kg in the aspiring and dispensing step. However, you should check the force required to eject tips, noting that ejection forces can be much higher than plunger forces.

Some ergonomic pipette models are equipped with an additional trigger that controls the aspiring step. You pull this trigger with your forefinger to aspirate a liquid before dispensing it by depressing the plunger with the thumb. Forces that could overstrain your fingers are thus significantly reduced.

Push the button

The easiest way to get rid of the plunger force associated with manual pipettes, however, is to buy an electronic pipette. Instead of pushing the plunger with your thumb, you simply touch a button. Though the plunger force is reduced to zero, electronic pipettes have some disadvantages. Prices are approximately two times higher than that of manual pipettes and some models are rather heavy.

The typical weight of an electronic single-channel pipette ranges between 150 and 300 g, in contrast to weights of between 90 and 140 g in manual pipettes. Nevertheless, an electronic pipette may be the right choice, especially if you are working with 96-multiwell plates requiring a multichannel pipette.

Pipetting slaves made of steel

If you are planning high throughput applications in your lab, such as screening assays that rely on 96- or 384-well plates, consider buying a pipetting robot. Pipetting slaves made of steel and plastic free you from mundane and time-consuming pipetting. They never grumble about repetitive pipetting for hours, work faster than the best skilled technician and make almost no errors so long as they are properly programmed.

Sounds too good to be true? There is indeed one small drawback: pipetting robots are expensive. You can easily spend 20.000 to 50.000 euros on a liquid handling robot. But they do almost anything for you, including RNA, DNA and protein purification, SNP-genotyping, sample preparation for MALDI-TOF mass spectrometry, powder dispension, real time PCR sample preparation and so on. Most liquid handling robots can be integrated into bigger workstations or can serve as an interface to other equipment such as plate readers and washers.

Over the next few pages you will find more detailed information about the pipettes and pipetting robots that are currently on the market.

(First Published: Harald Zähringer, Lab Times 02/2006. We expressly disclaim liability for this information.)