I’m working with cold Universal Transport Media and after dispensing, if the tips hang for even 10 seconds, it starts dripping a ton. I’ve made several adjustments to the liquid class (slower dispense speeds, higher dispense speeds, settling time, etc) and added a side touch, all to no avail. Any suggestions?
Several reasons possible, but one could be high evaporation that leads to overpressure in the air-chamber and therefore to dripping. some possible solutions:
- try to add 10 mixing-cycles to the aspiration, this should saturate the air and reduce drippage.
- add transport air 20ul or so, doesnt solve the problem but gives you some time
- activate ADC, might help in certain scenarios
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Like @J_can_do said, liquids with a high vapor pressure increases the pressure in the airgap of the tip that is above the aspirated liquid and below the plunger. As this pressure increases it forces liquid out of the tip to relieve the pressure since that airgap is totally closed to the outside environment. This is very likely what you are experiencing.
So another thing you can consider would be to increase the blowout volume to something significant that still keeps you within the volume limits of the channel. This way the aspirated liquid would need to vaporize more and longer in order to increase the pressure in that aforementioned airgap and begin to drip. For example, if you are transferring 500µL with 1000µL tips then you can technically set the blowout volume to ~750µLs (keeping in mind that you have to consider correction curve points as well).
Another thing that I have done that shows improved performance is to not just do a premix of the liquid a few times, but instead do a full (max volume) aspiration of the liquid where the command completes and the tips return to the traverse height. Then dispense all of that back to the source and proceed with your transfers to the real target.
Matt
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The first thing you have to be clear on is where the dripping comes from, because that heavily changes the measures you have to take. If it’s from inside the tip then you can do the steps described by the others above. If your liquid is volatile, anti droplet control works really well. If it’s higher density, honey like-ish, then it may be sheer gravity that pulls it down. Depending on the type of liquid, rather than trying to get the last bit of liquid off, it may be better to just aspirate a bit more, dispense what you want, and return the rest to the source container. This helps a lot if you have an adherent liquid that sticks to the inside of your tip and will slowly come down after dispensing.
All of this does not help if the dripping comes from the outside of the tip, due to adherent liquid. You can generally avoid this by using liquid level detection, minimizing the contact surface between tip and liquid.
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