How to Use a Pipette Correctly: A Short Guide for Beginners

Pipettes are essential tools for measuring and transferring small amounts of liquid in scientific research. They can help you perform experiments and tests with accuracy and precision. However, pipetting can also be a source of error and variability if not done properly. In this article, we will show you how to use a pipette correctly and avoid common mistakes that can affect your results.

What is a Pipette?

A pipette is a device that uses air pressure or vacuum to draw up and dispense a fixed or variable volume of liquid. There are different types of pipettes, such as air-displacement pipettes, positive-displacement pipettes, and repeater pipettes, each with its own advantages and disadvantages. The most common type of pipette is the air-displacement pipette, which uses a piston to create a vacuum in the tip and draw up the liquid. The volume of the liquid is determined by the position of the piston, which can be adjusted by turning a dial or pressing a button.

How to Use an Air-Displacement Pipette?

An air-displacement pipette consists of three main parts: the body, the plunger, and the tip. The body contains the piston and the volume indicator. The plunger has two stops: the first stop corresponds to the set volume, and the second stop corresponds to an extra volume that expels any remaining liquid in the tip. The tip is a disposable plastic cone that attaches to the body and holds the liquid.

To use an air-displacement pipette correctly, follow these steps:

1. Set the volume on the pipette by turning the dial or pressing the button until the desired volume is displayed on the indicator.
2. Attach a new tip to the pipette by gently pushing it onto the tip cone until it clicks into place.
3. Optional: Pre-wet the tip by aspirating and dispensing the liquid three times before taking the final sample. This will ensure that the tip is at the same temperature and humidity as the liquid and prevent evaporation or condensation.
4. Hold the pipette vertically and immerse the tip slightly into the liquid (about 2-3 mm for aqueous solutions and 6-10 mm for organic solvents). Avoid touching the bottom or sides of the container to prevent contamination or bubbles.
5. Press the plunger smoothly to the first stop and release it slowly to aspirate the liquid into the tip. Wait for about one second before removing the tip from the liquid to allow it to stabilize.
6. Transfer the liquid to the target container by touching the tip against the inner wall at a 20-45 degree angle. Press the plunger smoothly to the first stop and then to the second stop to dispense all of the liquid in the tip. Wait for about one second before removing the tip from the container to allow it to drain.
7. Eject the used tip into a waste bin by pressing the ejector button on the pipette. Do not reuse the tip as this can cause cross-contamination or inaccurate measurements.

How to Avoid Common Pipetting Errors?

Pipetting errors can arise from various factors, such as human error, environmental conditions, pipette calibration, tip quality, and liquid properties. Some of these factors are unavoidable, but others can be minimized or eliminated by following good pipetting practices. Here are some tips to avoid common pipetting errors:

• Use the right type and size of pipette and tip for your application. For example, use positive-displacement pipettes for viscous or volatile liquids, and use narrow-bore tips for low-volume measurements.
• Check the pipette calibration regularly and recalibrate it if necessary. Follow the manufacturer’s instructions for calibration and maintenance of your pipette.
• Use quality tips that fit your pipette well and are free of defects or contaminants. Discard any tips that are cracked, bent, dirty, or wet.
• Use the same technique for aspirating and dispensing every time. Avoid changing the speed, angle, depth, or pressure of your pipetting actions as this can affect the volume delivery.
• Use the reverse pipetting technique for foamy or viscous liquids. This involves aspirating more than the set volume by pressing the plunger to the second stop, and dispensing only the set volume by pressing the plunger to the first stop.
• Avoid exposing your pipette or tips to extreme temperatures or humidity changes as this can cause condensation or evaporation in the tip.
• Avoid mixing different liquids in the same tip as this can cause dilution or chemical reactions.
• Avoid pipetting air bubbles or droplets as this can cause inaccurate measurements or clogging of the tip.

Conclusion

Pipetting is a skill that requires practice and attention to detail. By following the steps and tips outlined in this article, you can improve your pipetting technique and ensure reliable and reproducible results. Remember to always use a clean and calibrated pipette, a new and appropriate tip, and a consistent and smooth pipetting action. Happy pipetting! 😊