It seems that one of our labs is having an issue with over dispensing on a normalization method that uses a transfer from file command. It seems that the dispensed volume is consistently off by about 1.5ul between the ranges of 10 and 45ul. In the Technique Editor “blowout all leading air gaps” is checked.
Does this option essentially “empty tips” as it does in a single dispense step?
The “Blowout all leading air gaps” should, in theory, just get rid of any air in the bottom of the tip that was aspirated to prevent leakage during the transfer. It’s not the same as the “empty tips” option.
If your over-dispense is very consistent, probably the easiest way to fix it will be in the Calibration tab. Just put in a fixed -1.5 uL adjustment there. You might want to adjust the aspirate volume in the same way to avoid wasting material, if you’re dispensing all the liquid you aspirate.
The Liquid Type tab might also be useful if you don’t want the quick-and-dirty fix above. It could be that your pipetting speeds need adjustment. But this is probably a more laborious way to fix your problem.
Thanks for confirming that. I was fairly certain that was the case but needed someone else to verify as a sanity check. I think we’ll probably opt for the quick and dirty method before going down the rabbit hole of adjusting the pipetting speeds.
I believe what you’re talking about here would be called a “trailing air gap.” Which also doesn’t have an option to “blow out” because it must get dispensed prior to dispensing your liquid. A leading air gap is aspirated prior to your liquid (it leads the liquid) and is used to blow out any additional liquid that gets stuck in the tip. Or, if you have a liquid displacement system (like a Tecan or perhaps a Beckman with a Span-8) you can use additional leading air gaps to make sure you aren’t diluting your sample with system liquid when you use fixed tips.
In theory, a blowout shouldn’t cause you to over dispense, unless you aspirated an overage, in which case the overage would get dispensed prior to blowing out your leading air gap.
My bad, you’re right. I got the terms mixed up.
