Factors influencing pipetting
Numerous factors influence the effectiveness of pipetting, including the sampling apparatus (pipette and tip), the environment, the sample and the user.
Pipette/tip
- badly calibrated or uncalibrated pipette
- inappropriate tip
- damaged tip
- damaged seal
- damaged pipette (corrosive liquid vapor, aspirated liquid…)
Environment
- ambient temperature
- relative humidity
- altitude
Sample
- temperature
- density
- viscosity
- volatility
Drag and drop the pictures corresponding to a correct pipetting
Immersing the tip too deeply causes compression of the air cushion, leading to an intake of liquid in excess of the setpoint. It also increases the risk of droplets remaining on the outside of the tip which can also be transferred and distort the delivered volume.
The pipette angle must be as close as possible to the vertical (between 0 and 20°). The further away from the vertical, the lower the liquid level will be, compared to the target level.
Abrupt moves when pushing in or releasing the piston must be avoided. An uncontrolled intake can generate bubbles, aerosols and contamination of the pipette.
Dispensing by pressing the end of the tip against the side of the container ensures the correct volume of sample (reducing or eliminating the residual amount).
For volumes in the µL, range, skimming the surface of the liquid draws the droplet out of the tip, which ensures better dispensing.
To learn more
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Some additional advice:
- Avoid temperature variations
- Air displacement micropipettes are sensitive to the difference in temperature between the air of the cushion and the sample to be withdrawn. Cold liquids tend to be over-dispensed, while hot liquids tend to be under-dispensed. If the sample permits, allow enough time to reach thermal equilibrium. Otherwise, use a positive displacement micropipette (see usage restrictions)
- Pre-rinse the tips
- After attaching the tip to the pipette, aspirate and dispense at least twice, because this will limit evaporation at the tip end. This is especially required for volumes in the µL range.
- Precise and correct pipette?
