How to achieve the best accuracy in liquid handling

Answer

When it comes to liquid handling, every scientist will say accuracy is always important. Their volumes need to be correct and if their pipettes aren't up to standard they will get them calibrated. In reality, when transferring > 10 µL of liquid, a scientist may not notice the volume is a few microlitres off (until their experiment fails and they troubleshoot the method).

Of course the right pipette tip size and module should be used for best accuracy, but if using a workflow that spans a wide volume range then accuracy may have to be sacrificed somewhere or adjustments made to the workflow. Instead of transferring one really large volume, complete two transfers with smaller volumes. Instead of one really low volume of high concentration, include a dilution step and transfer from the diluted solution.

If the ultimate goal is to have a full 96 MWP for PIXL to pick from then volume accuracy is unlikely to be your priority. Instead a liquid class with a faster flow rate and using the aliquot (multi-dispense) operation which is slightly less accurate than transfer, could be a speedier solution. However, if using expensive reagents, using low volumes or conducting a quantitative assay then volume accuracy isn't something that should be sacrificed on.

The question should be: what volume does my result actually require? If exact accuracy is not needed, then keep in mind what volume deviation would be acceptable to you when you are designing your workflow. There is always a sacrifice made somewhere in the workflow when accuracy is considered. A more accurate workflow is often a lot slower, both in workflow optimisation and the time taken per run. Less accurate would mean the speed can increase but there is a greater risk of errors and the volumes may be inconsistent. Usually, a successful workflow is somewhere in between the two positions, but that is the users decision to make for their application.

Other factors which affect accuracy

• Date since last calibration (recommended every 6 months)
  • See Cleaning, Calibration and Maintenance section
• All tips are able to "fit" all modules
  • A 10 µL tip on a 1000 µL module will show worse accuracy than a 10 µL tip on the 50 µL module
• The larger the range of the pipette module, less precision
  • The larger the range of the tip, less precision

Best practice tips

• • Don't go below 10% tip fill volume (e.g. for a 50 µL tip, best performance is down to 5 µL)
  • Lower than 10% is achievable and may give good results depending on the liquid, but ensure customer expectations are managed
  • The precision and accuracy are affected by how a liquid is pipetted, including the speed of pipetting

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