Techniques to improve liquid transfer consistency

Introduction

Manual pipetting is a fundamental skill in scientific research labs, one that every researcher has to master early in their career. While it may seem straightforward, achieving precision and consistency requires practice and attention to detail. To help you perfect this essential technique, here are some tried and tested tips, honed since the Gilson pipette first appeared in the 70s. 

Care for yourself and your pipette

Let’s establish the fundamentals. Having good posture and neutral wrists is essential if you intend to pipette for long periods of time sustainably. Sit or stand with your back straight and relaxed shoulders. Rest your pipetting support elbow on the work area and hold the pipette with a relaxed grip, keeping your wrist straight and neutral. Position your sample close to you and at a comfortable height. If your lab bench isn’t naturally the correct height for you, then take a seat on a lab-chair and adjust the seat to your needs. If you don’t often pipette you may still find that your hands and shoulders will tire quickly. Take regular breaks and allow yourself to rest otherwise your precision and accuracy will reduce over time.

Pipettes also need to be cared for to be effective, they require:
• Annual calibration & regular cleaning.
• Storage in a stable upright position to prevent damage.
• Plastic filter tips to prevent pipette/sample cross contamination.
Taking these steps will not only enhance the accuracy of your results, but also extend the lifespan of your pipettes, helping you achieve reliable liquid transfer in your experiments.

Tricky liquid transfers

As the volume transferred reduces, pipetting gets physically harder and less accurate. You should use a reverse pipetting technique (aspirate a larger volume than you dispense) especially with volatile or viscous liquids. If you can, transfer the low volume sample into liquid, the fluid already in the destination will help draw the sample out of the tip.

If you must transfer onto a dry surface, then lightly brush the end of the pipette tip onto the labware as you dispense, the droplet should adhere to the surface and help draw it out of the pipette tip. Lastly, keep the pipette vertical as variations in the angle can cause errors at volumes below 10 µL. 

Pipetting becomes significantly more challenging when the liquid’s temperature differs from that of the room. To maintain accuracy, let the sample reach room temperature before pipetting (unless it’s temperature-sensitive). If this isn’t possible, pre-wet the pipette tip several times to acclimatise the air inside the tip to the liquid’s conditions. Be aware that the greater the temperature difference, the less accurate and consistent your transfers will be. 

High-throughput assays

Multi-channel pipettes seem like a logical solution for larger assays across multi-well plates, but individual tips often fall off. To prevent this, press the pipette firmly into the tip box, and if a tip does fall off, eject the entire batch.

To achieve a greater consistency in well contents across the plate, prepare a master mix of the assay liquids, ensuring it’s thoroughly mixed. Then, use a reservoir to transfer the master mix into your multi-well plate.

“Sometimes multi-channel pipettes can be unreliable, For whatever reason one or two channels won’t fill properly. Then you’re like: what do I do with the sample now?” – Grace Ryall, PhD candidate

Multi-well plates are both the beauty and the beast of consistency when working with a manual pipette. Every sample has a uniform environment and can be processed in parallel. However, it’s extremely easy to lose your place, especially with colourless liquids in 96 or 384-well microplates. To avoid this, a researcher may eject the pipette tip into the well and leave it there as a place marker. This can risk external contamination but it’s an option. Alternatively, write out all your steps and check them off as you go. 

Human error

Mid-assay interruptions can be a source of inconsistency, this is especially commonplace in a communal lab. If you can, physically isolate yourself whilst you perform your assay, or conduct the assay at a time when fewer people are around. If these options are not possible: put on your most unapproachable expression, find some obnoxiously big headphones and hope for the best.

Fighting boredom is truly the biggest struggle when pipetting. It’s normal to be bored whilst filling 8x 96 multiwell plates with the same thing… again. When you’re bored, you’re not focused. Fight the monotony by transferring the liquid into alternate wells, or in diagonals rather than rows. And again, take breaks when you need to. Otherwise, you’ll end up spending 15 minutes staring into the abyss, only to realise you’re running late and panic. In your rush, you make a mistake or two, rendering your experiment useless and you just want to go home and cry. You think “maybe I should’ve had a new student do the task” but realise that you wouldn’t trust them to do it consistently anyway. If only you could be as soulless and unwavering as a machine in the face of a long slog of pipetting.

The reality is that whatever you do, everyone makes mistakes and nothing is as consistent as a well-programmed, precision robot.

Learn a new skill to set you up for your career in scientific research with lab automation. Discover more about the small, simple SQWERTY pipetting robot and expand your capabilities.

Need some pipetting advice?

Have a look at our growing library of resources written to support you on your liquid handling journey.

Fiona Kemm MRes | Scientist

Fiona is a vital member of our Research team, rigorously testing our robots to ensure scientists don’t break them. With no prior robotics experience, she was the ideal guinea pig for our world-class user experience and support. Holding a BSc in Biochemistry and an MRes in Molecular Microbiology, Fiona brings extensive hands-on expertise she applies across departments, supporting both users and internal teams. From writing insightful web articles to specialising in SQWERTY, Fiona ensures our innovations perform flawlessly, helping customers focus on the creative and interpretive aspects of science that can’t be automated.