Suggestions for better workflows

Answer

There are many settings and aspects of liquid handling devices that can be altered to optimise your workflow. It is always best to understand the terminology used and their effects to get the best out of your Pipetting Robot. Suggestions for better Pipetting should be read alongside this one.

Contents

• General
• Forward or direct pipetting (used interchangeably)
• Travelling Air Gap
• Pausing
• Immersion Depth
• Touch transfer
• Further tips on workflow design

General

• Allow labware & reagents to acclimatise to the lab environment.

• Using 80% of the total pipette volume generates an effective mix, but may require more tip eject steps.

• Reduce splashing by reducing the flow rate and an immersion depth of >0 mm.

Forward or direct pipetting (used interchangeably)

When the entire volume of the aspirate is dispensed in the target location in one go. Forward pipetting is often used with a manual pipette to transfer liquids and is suitable for most situations. Reverse pipetting means that the aspiration volume is greater than the volume dispensed. This is better for accuracy with lower volumes, viscous or foaming liquids; it ensures that the target volume is definitely met.

Travelling Air Gap

A travelling Air gap is the volume of air added after the aspirate to prevent any sample dripping. A blow out is the volume of air added before the aspirate to ensure the target volume is dispensed. This is the automated version of pushing the manual pipette to the second position to push out that small volume of additional air. Optimising these volumes is essential to get the best out of your workflow.

Pausing

Pausing after dispensing or aspirating can increase the consistency of the volume transferred, this is referred to as the dwell time. More viscous liquids like glycerol move slower through pipette tips, the dwell time allows time for the liquid to complete the transfer. Slowing the flow rate in the dispense and aspiration also has the same effect.

Immersion Depth

The immersion depth of the tip into the liquid is another aspect essential to accuracy and preventing contamination. This is the depth beneath the liquid surface that the tip travels to before aspirating or dispensing. If this is set too deep then there is a risk of the liquid clinging to the outside of the tip, ultimately increasing the volume transferred and also risking contamination if the drips fall outside of a well. If the depth is too shallow then there is a risk of air being aspirated instead of liquid resulting in a lower volume being transferred. As usual, these effects are exaggerated when working with small volumes. 1 cm is the usual recommended immersion depth.

The immersion depth can be set either manually or automatically. Liquid level detection and liquid level tracking are useful when the height of the liquid surface is unknown. The tip will detect the liquid surface by the pressure change and then travel the user defined extra travel before aspirating.

Liquid level detection and liquid level tracking may take a little time to optimise and can be slower than the manual immersion depth (depending on Liquid level detection speed) but it is likely to be more accurate. Once the user knows the settings, that liquid class is easily added to any workflow which means a faster set up. Please refer to What are Liquid Classes and how to create new ones? (Video)

Touch transfer

Touch transfer is the word used for setting the pipette to travel to the bottom of the labware before dispensing. This requires the labware to be described as accurately as possible in the software, otherwise the tip will either stop short or crash into the bottom of the labware. A touch transfer is most useful at low volumes, to remove that extra volume that's adhering to the tip. The lowest volume SQWERTY is able to transfer onto a dry surface is 2 μl.

Further tips on workflow design

• To improve accuracy, always pre-wet the pipette tip before starting the multi-dispense or Transfer.
• The first and last transfers in a multi-dispense procedure are typically the least accurate. Dispense the first portion back into the source to ensure consistency, making the first target the source itself. Ensure that after dispensing into all targets, there's still one dispense worth of volume left in the pipette. This ensures that even if an earlier target received slightly more than intended, there will still be enough volume for the final target to receive the full intended amount.
• Liquid level detection and liquid level tracking give the greatest degree of accuracy but only if you're willing to put some resource towards optimising for your labware and liquids. Liquid Level Tracking can easily be inaccurate if the object assigned in the software is not the same as the one used in the hardware. Liquid Level Detection can be slow and accurate but can also be faster but potentially less accurate. 
• If you use Liquid Level Tracking in combination with manually setting the insertion depth - be sure that you know the depth of the labware you're using. There's a risk otherwise of setting the immersion depth too near the well/tube base and Liquid Level Tracking will cause the tip to crash into the bottom. 

If you require more information please contact [e-mail] for assistance.