Suggestions for better Pipetting

Answer

This article covers suggestions to improve liquid pipetting. See also : Suggestions for better workflows

Suggestions

• Aspirate slow and dispense fast in general. 

  • Aspirate < 200 μl /s and dispense >250 μl /s

  • This prevents the formation of droplets on the tip after dispense.

• Viscous liquids should be aspirated & dispensed slowly with a longer dwell time and a contact with the labware or liquid surface.

• The pipetting speed should be the same as the volume aspirated but never exceeding the maximum flow rate for SQWERTY: 450 μl/s . 

• Samples should be free of any debris, foam/bubbles and droplets on the tube/well walls – lightly centrifuging will solve these problems

• Don’t overfill the container as it may cause it to overflow during stage movement or pipette tip insertion.

• Decreasing the aspiration flow rate will increase precision/accuracy.

  • 10-70 μl /s is recommended for volumes less than 30 μl  or with high viscosity or volatile fluids.

  • The faster the aspiration flow rate, the stronger the pull which could result in bubbles within the tip

• Use an aspiration dwell time of at least 300 ms especially with 1000 μl  tips. Higher viscosity liquids require further delays.

• The submerged depth should be as small as possible 1-2 mm if possible but no more than 1 cm.

• If using small volumes then add additional volume as a blow out / air gap / reverse pipetting.

  • When using a 250 μl pipette but transferring only 10 μl , add an additional 20 μl of volume with air or fluid.

• Liquids like detergents/ buffers should be dispensed slowly to avoid foaming

• Volumes lower than 20 μl need high dispense speed and a bigger air gap values to allow for it.

• Large volumes should be dispensed at a slower speed.

• 0 mm dispense for greater workflow speed with slightly less accuracy. Touch transfer or surface level dispense for lower throughput but higher accuracy.

• Air gap + Blow out should be less than 30 μl as there is no advantage to performance but the accuracy and precision may suffer.

  • The blowout should be bigger than the air gap and at least 5 μl to truly be effective.

• Liquids with high vapour pressure need to be pre-wet to avoid liquid loss through evaporation. Do this up to 3 times but don’t spend too long as the delays could cause further liquid loss from the source via evaporation.

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