Proper pipetting comes down to smooth, consistent movements and a few technical details that most people never learn formally. Small errors in angle, speed, or immersion depth can throw off your volume by enough to ruin an experiment. Here’s how to get it right every time.
Forward Pipetting: The Standard Technique
Forward pipetting is the default method for most aqueous solutions. It uses two distinct plunger positions, called the first stop and the second stop, and the sequence matters.
To aspirate, press the plunger down to the first stop before you place the tip into your liquid. Then immerse the tip and slowly release the plunger to draw up your set volume. Pressing to the first stop before immersion (not after) prevents you from pushing air into your sample. To dispense, touch the tip against the inner wall of your receiving vessel and press the plunger to the first stop. Then, while still pressing, drag the tip up the wall and push through to the second stop. That final push, the “blowout,” clears the last bit of liquid from the tip.
Hold the pipette nearly vertical during aspiration. Tilting it significantly lets liquid creep up the inside of the tip, which affects your volume and risks contaminating the pipette barrel. When dispensing, angle the tip 10 to 45 degrees against the vessel wall so the liquid transfers cleanly.
Reverse Pipetting for Tricky Liquids
Some liquids don’t behave well with forward pipetting. Viscous solutions like glycerol coat the inside of the tip, oils form a film on plastic, volatile solvents evaporate during the transfer, and foaming liquids trap air when you blow out. Reverse pipetting solves all of these problems.
The method flips the plunger logic. You press all the way to the second stop before aspirating, which draws up more liquid than your target volume. When you dispense, you press only to the first stop, delivering exactly your target volume while leaving the excess behind in the tip. That excess absorbs the losses from adhesion, evaporation, or film formation that would otherwise short your delivery. The leftover liquid in the tip gets discarded or returned to the source.
For foaming liquids, the advantage is that you never need a blowout, so you avoid forcing air through the sample and generating foam. For oils and viscous solutions, the liquid that clings to the tip walls comes from the excess rather than from your measured volume.
Pre-Wetting Improves Accuracy
Before you transfer any sample, aspirate and dispense the liquid three times at your set volume using the same tip. This pre-wetting step equalizes the temperature between your liquid and the air cushion inside the pipette, and it humidifies that air space so less liquid evaporates during the actual transfer.
Pre-wetting matters most for volumes above 10 µL and is especially important for volatile samples like organic solvents. For volatile liquids, five or more pre-wetting cycles are recommended. For viscous solutions, oils, and foaming liquids, three to five cycles are a good baseline. Skipping this step is one of the most common reasons for inconsistent results, particularly at the start of a pipetting session.
Immersion Depth and Speed
How deep you dip the tip matters more than most people realize. Too deep, and droplets form on the outside of the tip that get carried along with your sample, inflating your volume. Too shallow, and the tip sucks in air instead of liquid. The correct depth depends on your volume range:
- 0.1 to 1 µL: 1 mm
- 1 to 100 µL: 2 to 3 mm
- 101 to 1,000 µL: 2 to 4 mm
- Above 1 mL: 3 to 6 mm
These are surprisingly shallow. Most beginners plunge the tip far too deep, which is why they get extra liquid clinging to the outside.
Speed is the other half of the equation. Aspirating too quickly can pull air bubbles into the tip, especially with viscous liquids, and it increases the risk of liquid splashing up into the pipette barrel. For thick or sticky samples, slow your aspiration noticeably and keep the tip immersed a beat longer than usual before withdrawing. For standard aqueous solutions, a smooth, steady release of the plunger is sufficient.
Temperature and Environment
Air-displacement pipettes are calibrated at 22°C (about 72°F). When your liquid is warmer or cooler than that, the air cushion inside the pipette expands or contracts differently than expected, creating a systematic volume error. A warm liquid causes the air cushion to expand more during aspiration, delivering excess volume. A cold liquid does the opposite.
If you’re working with liquids that are significantly above or below room temperature, pre-wetting becomes even more critical because it helps the air inside the pipette adjust. For high-precision work, let refrigerated reagents come closer to room temperature before pipetting, or use a positive-displacement pipette that eliminates the air cushion entirely.
Choosing the Right Tips
Standard tips work for routine liquid handling, but certain applications call for filter tips. These contain a small barrier inside the tip that blocks aerosols and liquid from reaching the pipette barrel. You should use filter tips whenever cross-contamination could compromise your results: PCR, forensic work, genetic studies, or anything involving radioisotopes. They also protect the pipette itself from contamination if liquid accidentally gets aspirated too far.
Filter tips come in self-sealing and standard filter versions. Self-sealing barriers actively block passage of aerosols, liquids, and biological material even under pressure. Either type prevents you from having to decontaminate the inside of your pipette after an accidental over-aspiration.
Always use tips designed for your specific pipette brand and model. A poor seal between the tip and the pipette cone introduces air leaks that degrade both accuracy and precision.
Ergonomics for Long Sessions
Pipetting for more than one hour a day increases your risk of repetitive strain injury. That’s a lower threshold than most lab workers expect, and many people blow past it regularly during cell culture, sample prep, or plate loading.
If you pipette for extended periods, take micro-breaks every 20 to 30 minutes. During those breaks, loosen your grip, stretch your fingers, and relax your hand and forearm. A V-shaped or cut-out bench that lets you sit closer to your work reduces the reach and shoulder strain that builds up over a session. Remove anything under the bench that prevents your knees from fitting comfortably underneath, since perching at the edge of your seat throws off your posture and puts more strain on your thumb and wrist.
Consider using an electronic or lightweight pipette if you’re doing high-throughput work. The force required to push through the second stop on a manual pipette is the single biggest contributor to thumb fatigue over a long day.
Keeping Your Pipette Accurate
A pipette that isn’t regularly checked drifts out of calibration without any obvious sign. ISO 8655 requires users to establish routine testing schedules, and most labs check calibration every 3 to 12 months depending on use frequency. If a routine check shows the pipette is delivering outside its specified tolerance, many models allow user adjustment before sending the instrument out for professional calibration.
For daily maintenance, wipe down the exterior and check that the tip ejector and plunger move smoothly. Be cautious with cleaning agents: prolonged or repeated exposure to alcohol-based disinfectants like 70% ethanol can swell and harden rubber seals and damage certain plastics over time. For decontamination that won’t harm internal components, glutaraldehyde-based solutions have excellent material compatibility with metals, rubber, and plastics. Always check your pipette manufacturer’s cleaning guidelines before using any chemical disinfectant on internal parts.
Store pipettes vertically on a stand or carousel when not in use. Leaving a pipette on its side, especially with liquid residue near the barrel, lets fluid seep into the piston mechanism and corrode internal components.