How do I improve my pipetting results?

Liquid handling is sensitive to factors like liquid properties and the environment of your lab. To get the results you want, you may need to adjust some of the more advanced settings that the Microlab Prep offers. This article describes different ways to fine-tune the settings in pipetting steps to optimize your results.

Requirements

• A completed protocol to test and improve

Procedure

Before making any changes to your protocol, double-check that a liquid type is available that is similar to your liquid in terms of properties. The most important properties to consider when selecting a similar liquid type are viscosity and vapor pressure (volatility). If the available liquid types are not close enough to yours, the Prep has several options for managing unknown liquids.

Default Liquid Type	Aqueous	Ethanol	DMSO	Glycerol	Serum
Example Adjusted Liquid Types	PBS	Isopropanol	Alkane	Oil	Plasma
	TRIS	Acetone			Red blood cell
		Formaldehyde

Simple Fixes

The Pipetting Settings page contains several simple options that can improve results. Try different potential fixes individually and test the results to see what works best for your protocol.

1. Open the desired step for editing, then navigate to the Pipetting Settings page.
2. Try each of the following potential fixes and compare the results. Make sure to test each change separately, so you know what to adjust in other protocols in the future.
   • Pre-wet the tip(s) by adding a mix before aspirate.
     Mixing can be used to pre-wet a tip before aspirating, which can improve the accuracy of the aspiration. A pre-wet is especially useful when pipetting volatile liquids, as it helps prevent dripping between aspiration and dispense. Enable a mix before aspirating either in the General tab or the Aspirate tab of the Pipetting Settings.
     
   • Add extra aspirate volume. Extra aspirate volume can bring low dispense volumes closer to the target volume. The excess liquid in the tip after dispensing is automatically emptied to the liquid waste. Open the Aspirate tab and either tap the “Aspirate volume” field or use the + button to add extra aspirate volume.
     
   • Check the settings for your pre- and post-aliquots (multi-dispense only). Pre- and post-aliquots of 20 µL are automatically enabled when multi-dispensing in an Add Reagent or Serial Dilution step. Open the Dispense tab and tap the Multi-Dispense tab to view and edit the aliquot settings.
     
     For best results, follow these guidelines:
     
     • For multi-dispense volumes less than ¼ of the tip volume, set the pre- and post-aliquot volumes equal to the volume per well.
       
     • For multi-dispense volumes greater than ¼ of the tip volume, disable the pre- and post-aliquots.
       

Liquid Parameters

In the Liquid tab of a Pipetting Settings page, the liquid Parameters can be adjusted to fine-tune how a liquid is pipetted. Any changes will only apply to the step being edited, unless the changes are saved as a new liquid to use in other steps or protocols.

Changes to the parameters are linked to the selected liquid type, tip type, and where the dispense position is measured from. If any of these settings are changed, changes to the parameters will be lost.

1. Open the desired step for editing, then navigate to the Pipetting Settings page.
2. Open the Liquid tab and check “Override defaults”. The liquid parameters can now be edited.
3. Adjust the liquid parameters and test your changes. Make sure to test each change separately, so you know what to adjust in other protocols in the future.
   • Pipetting speed: The rate that liquid is aspirated or dispensed in µL/s, controlled by the speed of the plunger in the pipetting head. Slower speeds are better for smaller tips, high-viscosity liquids, and dispenses at the container bottom or in existing liquid. Faster speeds are better for volatile liquids and dispensing above the container bottom or the liquid level.
     
     Keep in mind that the pipetting speed can vary greatly depending on the liquid type, and adjusting the speed can impact volume accuracy.
     
   • Blowout volume: The volume of air in µL aspirated before aspirating liquid. It is dispensed last to help drive out all liquid in the tip. High blowout volume can help dispense especially high-viscosity liquids and low volumes.
     
     Keep in mind that blowout volumes that are too high can cause aerosols or bubbles to form when dispensing at or below the liquid level.
     
   • Swap speed: The speed in mm/s that tips are raised out of the liquid. Slow swap speeds are useful for high-viscosity liquids, while faster swap speeds are useful when pipetting volatile liquids.
     
     Keep in mind that the swap speed must be carefully controlled to prevent droplet formation.
     
   • Settling time: The time in seconds that the tip remains in the liquid after pipetting before moving up. Liquids that are high-viscosity or dispensed at the bottom of empty containers require a longer settling time.
     
     Keep in mind that most liquids do not require a long settling time; volatile liquids require an especially short settling time.
     
   • Air transport: The volume of air in µL aspirated after the liquid volume. Air transport volume is aspirated after the tip is raised out of the liquid to prevent droplet formation and dripping between aspiration and dispense.
     
     Volatile liquids require a larger air transport volume compared to other liquids, but the air transport volume should always be lower than the liquid volume. When pipetting liquid volumes below 10% of the tip volume, an air transport of 0 may improve performance.
     

Correction Curve

Each liquid has a correction curve of volumes to account for environmental factors and differences in liquid properties that can impact pipetting accuracy. Values can be edited or added to adapt the curve to your lab environment and fine-tune your results.

Changes to the correction curve are linked to the selected liquid type, tip type, and where the dispense position is measured from. If any of these settings is changed, changes to the correction curve will be lost.

1. Open the desired step for editing, then navigate to the Pipetting Settings page.
2. Open the Liquid tab, then tap “Correction Curve”.
3. Check “Override defaults”. The correction curve values for the current liquid type and tip type will appear.
4. Tap a field to edit the adjusted volume, or tap “Add correction point” to add new values, then enter the new updated volume(s). Make sure to test each change to the correction curve separately, so you know what to adjust in other protocols in the future.