Widely used and used in a variety of laboratories, mechanical pipettes are durable tools. They are typically used for several hours a day, so ergonomics and personal preference, including operator comfort, are crucial selection criteria.
When looking for the best pipette for the job, other relevant factors must also be considered, such as the application, laboratory workflow, physical properties of the sample, desired volume range, and requirements for accuracy and precision.
Accuracy and Precision
Accuracy and precision are the two main aspects of choosing a good pipette. Accuracy means that the delivered volume meets the set volume. Precision is an expression of how close several pipetting results are. Here are some examples:
accurate but not accurate
The results are accurate but not accurate: the average volume agrees with the set volume, but individual pipetting results differ from each other.
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accurate but not accurate
Results are precise but inaccurate: there is only a small difference between pipetting results; however, the average volume is independent of the set volume.
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precise and accurate
Results are accurate and accurate: the average volume equals the set volume; there are only minor differences between pipetting results.
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The terms Accuracy and Precision are shown in the pipette's specification as Systematic Error % (Inaccuracy %) and Random Error % (Inaccuracy %). It is important to note that these specifications are only valid when using the manufacturer's own pipette tips.
Best accuracy is achieved with high quality, professionally calibrated and well maintained pipettes and the necessary high quality tips. On the other hand, precision is largely influenced by pipetting experience and good laboratory practices, such as proper pipetting angle, consistent pipetting rhythm, and optimal pipetting speed.
To ensure the highest level of accuracy, the user should select the smallest volume pipette capable of handling the relevant volume. This is critical as pipetting accuracy decreases when the volume dispensed approaches the minimum volume of the pipette.
For example, using a 1 ml pipette when dispensing 10 μl of liquid will result in poor precision, a 300 μl pipette is better, and a 10 μl pipette is even better.
Additionally, to ensure good pipetting results, it is critical to choose a pipette with low pipetting, tip loading and tip ejection forces.
High forces are more likely to cause arm and hand muscle fatigue, leading to the risk of insufficient results, especially in long pipetting series. Users are advised to be aware of the following characteristics, which can affect the performance and reliability of pipetting results:
Color coding of the pipette or pipette cap - this helps the user select the correct tip for the pipette.
Easily calibrate different kinds of liquids. It is also beneficial if the settings can be saved for later use.
Volume Adjustment Lock - This feature helps reduce accidental volume changes during pipetting. Special attention should also be paid to the reliability, ergonomics and intuitiveness of the mechanism.
Ergonomics
Pipetting is one of the most frequently performed tasks in the laboratory. Studies have shown that continuous pipetting is associated with an increased risk of upper extremity musculoskeletal disorders, with over 40% of laboratory professionals potentially suffering from pipetting-related disorders. *
In addition to causing discomfort, hand or arm injuries can limit performance levels and can have knock-on effects when it comes to accuracy, precision, and reliability of results. In order to be as ergonomic as possible, it is important to pay close attention to the following qualities when choosing a pipette:
Grip Design and Balance
The fit between the pipette and hand should be comfortable, and the finger support should make holding the pipette effortless. Additionally, a well-balanced pipette with a center of mass close to the palm provides stability, greatly reducing hand muscle strain and wrist torque.
Required pipetting force
As pipetting force increases, so does the risk of RSI. Additionally, it reduces the accuracy and precision of long pipetting series. The force required to move the plunger to the first stop is typically between 3 and 15 N. However, the force required to press the plunger to the second stop can reach 40 N.
A simple test can compare the pipetting force of two pipettes by pressing the plungers against each other. The plunger showing the lower pipetting force will move first.
Suitable for right- and left-handed users
The pipette should be suitable for right-handed and left-handed users. All operations should work equally well in both directions. Also, the display should be easy to read regardless of orientation.
suction head output
Tip ejection usually requires more force than pipetting. The high tip ejection force of mechanical pipettes can pose a risk of injury, especially when performing repetitive pipetting. Typical tip ejection forces range from 15 to 30 N.
Tip loading
In addition to tip ejection, tip loading requires the greatest force during the entire pipetting process. Tip loading force is the force required to securely attach the tip to the pipette. Unsuitable tips need to be tapped, shaken or even hand-tightened to ensure proper sealing. Forces can be limited by using properly fitted tips.
Range display
To prevent the pipette from being in an awkward position, the volume should be easy to read during normal pipetting. Also, the larger the number, the easier it is to read.
Range adjustment
Adjusting the pipetting volume should be easy and ergonomic. To prevent any unnecessary pressure on the thumb, it should be easy to adjust the volume with both hands - hold the pipette with one hand and turn the adjustment wheel with the other.
weight and length
If the pipette is lighter and shorter, it is more ergonomic.
*Bjorksten, MG, B. Almby and E., S. Jansson. 1994, Frederickson, K. 1995
prevent pollution
To prevent the spread of aerosols or sample droplets when the tip is ejected, make sure to choose a pipette with gentle tip ejection. When the tip is gently ejected, the droplets or aerosols left behind are less likely to spread over a large area.
For quick, convenient decontamination procedures, choose mechanical pipettes that can be autoclaved without disassembly - this is also available on multi-channel models. The choice of pipettes should be based on the possibility they offer the use of filters on the tip cones.
The cone filter prevents aerosols and liquids from entering the internal components of the pipette. They are also a frugal and efficient way to avoid sample contamination. Alternatively, filtered pipette tips can be used in the application.
Single-channel or multi-channel pipettes?
Single channel pipettes are the workhorse of liquid handling. They are available in a range of adjustable and fixed volume models. Adjustable volume pipettes mean that the volume dispensed can be changed as needed, while fixed volume pipettes always dispense the same amount of liquid each time.
Fixed volume pipettes prevent dispensing errors due to incorrect volume selection. They are ideal for applications with constant fluid delivery and are ideal for beginners and non-certified technicians.
Here are the most important points to consider when choosing a multichannel pipette:
Check the position of the lower part of the pipette to see if the pipette can be adjusted 360 degrees to ensure ergonomic pipetting.
Check that the tip can be easily ejected.
Make sure the pipette provides fast, safe and simultaneous tip loading for all tips. It should be possible to install the tip evenly without too much force.
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Air or volumetric pipettes?
There are two types of mechanical piston pipettes: air displacement pipettes and volumetric pipettes.
Developed with general laboratory work and water samples in mind, air displacement pipettes have an air column between the piston and the liquid. This type of pipette is used for most pipetting work in the laboratory.
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How Air Displacement Pipettes Work
Volumetric pipettes are designed to handle demanding samples such as extremely viscous, volatile, radioactive or corrosive liquids. With this pipette, the plunger is in direct contact with the liquid, reducing the risk of contamination to near zero.
Volumetric pipettes require the use of special tips and are therefore more expensive than air displacement pipettes.
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