BIOTECHNOLOGY Changes in the pipette’s angle will
affect the hydrostatic pressure within the pipette tip
TIPS FOR PIPETTING
How to achieve error-free pipetting for accurate results By Noelia Teliz, Product Specialist, INTEGRA Biosciences
P
ipetting is one of the most common laboratory tasks, forming the cornerstone of scientific research and clinical
diagnostics. The impact of pipetting errors is often underestimated, but even slight discrepancies in precision – arising from both the instrument and the user – can accumulate over the course of a workflow, resulting in substantial inaccuracies in the final data. Pipetting by hand takes years of practice to perfect, but there are ways to quickly improve the accuracy of manual liquid handling for more reliable results.
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MANUAL PIPETTING BEST PRACTICES Firstly, changes in pipetting angle will affect the hydrostatic pressure within the pipette tip, resulting in an inconsistent aspiration volume. Holding a pipette at an angle of 20 degrees or less from the vertical is therefore paramount for consistent liquid aspiration and dispensing, and for very small volumes of ≤30, the straighter the pipette, the better. After dispensing, there will often be a droplet left behind at the end of the pipette tip. A simple way to make sure the whole sample is dispensed into the target vessel is to
perform a tip touch when removing the pipette from the vessel. There are three ways of doing this: side wall touch off, surface touch off, and direct dispensing into a liquid. Another common source of error
is caused by temperature differences between pipettes, tips and liquids. These can affect the air cushion inside the pipette, leading to volume variations. Incorporating a prewetting step into a pipetting routine helps to ensure that all labware and liquids are in equilibrium, largely overcoming this issue and providing more confidence in the accuracy of measurements. Some electronic handheld pipettes can even be programmed to include a prewetting step, making it easier to achieve precise and consistent results. During repeat dispenses, the first dispense may be too low in volume, and the final dispense could include all the accumulated errors of the previous dispenses. Discarding the first and last dispenses helps to eliminate these inconsistencies, resulting in more reliable aliquots. .
ENSURING ACCURATE VOLUME CONTROL Each pipette has an optimal volume range; for an air displacement pipette,
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