7. Examine the tip AFTER dispensing a sample
While dispensing a sample, position the tip to touch the side of the container to deliver any residual sample remaining in the tip. Keep your thumb pressed on the second stop of the plunger and remove the tip to avoid sample re-aspiration into the pipette tip. Make sure that you see the sample leaving the tip.
8.Use standard mode pipetting
Choose “standard (or forward) mode” pipetting rather than “reverse mode” for all aqueous samples. You might consider reverse pipetting for particularly viscous or volatile samples. If the reverse pipetting is used with normal aqueous samples, the pipette tends to deliver more than the calibrated volume. On the other hand, using the standard pipetting with viscous or volatile samples may result in under-delivery.
9.Use the appropriate pipette
It is important to use a pipette with a volume range closest to the volume you plan to aspirate and dispense. The accuracy of your test will improve if there is a slight difference between a pipette’s minimum volume and the volume being tested. For example, if you need to dispense 15 µL, a 1 mL pipette would be the wrong choice, whereas a 20 µL pipette would be ideal.
10.Use the correct pipette tip
Use high-quality tips intended for use with specific pipettes. In most cases, manufacturer tips perform well. Alternative brands are also acceptable if their performance has been proven with a specific pipette model. Mismatched tips and pipettes can result in inaccuracy, imprecision, or both. Quality pipette tips provide an airtight seal without the need for excessive force, are made of superior materials, and are free of molding defects, thus ensuring reliable liquid delivery.
11. Work at ambient temperature equilibrium
Allow liquids and equipment to reach an equilibrium at an ambient temperature before you begin pipetting. The volume of a sample delivered by air displacement pipettes varies with air pressure, relative humidity, and the liquid’s vapor pressure, all of which are temperature-dependent properties. Working at a single, constant temperature minimizes this variation and improves overall precision.
12.Minimize pipette handling
Hold the pipette loosely, return it to the pipette stand or set it down when you are not pipetting. Always wear gloves to reduce body heat transfer to the pipette and avoid handling pipette tips or containers of samples yet to be pipetted. Body heat transferred during handling disturbs the temperature equilibrium, which can lead to variations in delivered volumes.
