A micropipette transfers tiny, precise volumes of liquid using a spring-loaded plunger and a disposable plastic tip. Learning to use one correctly comes down to understanding two plunger stops, a few key techniques, and consistent habits that protect both your results and the instrument.
How a Micropipette Works
Most micropipettes in research and clinical labs are air displacement pipettes. A piston moves inside a cylinder, and a small column of air sits between the piston and the liquid in the tip. When you press the plunger and release it, that air column creates a partial vacuum that draws liquid up into the tip. When you press the plunger again, the air pushes the liquid back out. The liquid never touches the internal mechanism, only the disposable tip.
Positive displacement pipettes work differently. The piston makes direct contact with the liquid inside a specialized disposable capillary tip. These are designed for liquids that cause problems for standard air displacement pipettes: viscous solutions, volatile solvents, or anything that tends to foam. For everyday water-based solutions, air displacement pipettes are the standard, and the technique below applies to them.
Key Parts to Know
The plunger button sits at the top and is operated with your thumb. It has a resting position and two stop positions you can feel as you press down. The volume adjustment dial (usually a rotating wheel or ring near the top) lets you set the desired volume, which displays in a small number window on the body. The shaft at the bottom is where disposable tips attach by friction fit. Next to the plunger, a tip ejector button lets you pop off a used tip without touching it.
Setting the Volume
Each micropipette covers a specific range, such as 0.5–10 µL, 2–20 µL, 20–200 µL, or 100–1000 µL. Never dial the volume above the maximum or below the minimum printed on the pipette. Doing so stretches or compresses the internal spring beyond its calibrated range and damages accuracy over time.
Turn the volume adjustment dial to your target number. If you overshoot and need to dial back down, go past your target and then turn back up to approach the number from below. This avoids mechanical slack in the dial that can throw off the setting slightly.
Step-by-Step: Aspirating and Dispensing
Hold the micropipette in a nearly vertical position, like a large pen, gripped in the hand with your thumb resting on the plunger. Attach a clean disposable tip by pressing the shaft firmly into the tip.
Aspirating (Drawing Liquid Up)
Press the plunger smoothly down to the first stop. You’ll feel a distinct resistance point. Hold it there. Immerse the tip just a few millimeters into the liquid surface. Going too deep introduces extra liquid clinging to the outside of the tip, and going too shallow pulls in air. Then release the plunger slowly and steadily. Let it glide back up on its own spring rather than snapping it. The set volume of liquid is now inside the tip.
Pause for about one second after the plunger returns fully. This lets the liquid finish moving into the tip, especially for volumes at the higher end of the pipette’s range. Then withdraw the tip from the liquid.
Dispensing (Pushing Liquid Out)
Touch the tip at a slight angle (roughly 10 to 45 degrees) against the inside wall of the receiving vessel. Press the plunger smoothly to the first stop. The liquid will flow out along the vessel wall. Wait one second, then continue pressing the plunger past the first stop to the second stop. This “blow-out” step pushes out the last tiny bit of liquid that clings inside the tip. Without it, you consistently deliver less than you intended.
While still holding the plunger at the second stop, slide the tip up along the wall to break contact with any remaining droplet, then release the plunger. Use the tip ejector button to discard the tip.
Pre-Wetting the Tip
Before you pipette your actual sample, aspirate and dispense the same liquid two or three times to “rinse” the inside of the tip. This step, called pre-wetting or pre-rinsing, neutralizes capillary effects inside the fresh plastic tip and balances the air temperature inside the tip with the temperature of your sample. It dramatically improves accuracy, especially when you’re working with very small volumes in the low microliter range. Skip this step only when you’re transferring between different solutions and cross-contamination would be a problem.
Reverse Pipetting for Tricky Liquids
Standard “forward” pipetting (described above) works well for water and most buffers. For viscous, foamy, or volatile liquids, reverse pipetting gives better results. The difference is where you start. Press the plunger all the way to the second stop before immersing in the liquid. Release to aspirate. This draws up slightly more than the set volume. When you dispense, press only to the first stop. The extra liquid stays in the tip, which you discard. Because you never use the blow-out step during dispensing, the volume you deliver is more consistent with difficult liquids.
Common Mistakes That Hurt Accuracy
- Pipetting too fast. Jerky plunger movements introduce air bubbles and produce inconsistent volumes. Smooth, steady pressure in both directions is essential.
- Holding the pipette at an angle during aspiration. Keep it nearly vertical when drawing liquid up. Tilting changes the effective depth of immersion and the air column geometry.
- Immersing the tip too deeply. Extra liquid coats the outside of the tip and gets carried over to your receiving vessel, inflating the volume you deliver.
- Skipping the blow-out. If you stop at the first stop and never press to the second, a small but consistent amount of liquid stays behind in the tip every time.
- Using the wrong size pipette. A 1000 µL pipette set to 50 µL will be far less accurate than a 200 µL pipette set to 50 µL. Always choose the pipette whose range best matches your target volume, ideally using the upper third of its range.
Ergonomics and Posture
Pipetting for hours is one of the most common causes of repetitive strain injuries in lab work, particularly in the thumb, wrist, and shoulder. Keep your wrists straight and avoid twisting or rotating them while pressing the plunger or ejecting tips. Grip the pipette firmly enough to control it but not so tightly that your hand fatigues quickly.
Keep your elbows close to your body and position your work slightly below elbow height. This reduces the need to raise your arms or hunch your shoulders. Adjust sample holders, waste bins, and solution containers so everything is within easy reach without bending your wrists. If you pipette frequently, take short breaks every 20 to 30 minutes and switch hands when possible.
Cleaning and Maintenance
Wipe down the outside of the pipette body regularly with a mild lab-safe disinfectant. If liquid gets aspirated into the body (usually from releasing the plunger too quickly or overfilling), disassemble the lower shaft according to the manufacturer’s instructions, clean the internal components, and let everything dry before reassembling.
Many micropipettes can be partially or fully autoclaved, but check your specific model first. Disposable tips are generally autoclavable on a steam-producing cycle, though in practice tips mostly go through the autoclave as waste inside biohazard bags rather than for reuse. Never autoclave sealed containers, and keep bleach and corrosive chemicals away from the autoclave entirely.
Calibration drifts over time, especially with heavy use. Most labs send pipettes out for professional calibration at least once a year. Between calibrations, you can do a quick gravimetric check yourself: pipette distilled water onto an analytical balance and compare the measured mass to the expected volume (1 µL of water at room temperature weighs approximately 1 mg). If your readings are consistently off by more than a few percent, the pipette needs service.