Touch off with MPH

Hi there,

I’m seeking your help once again. When pipetting with the 1000 uL channels, I can use the touch off option, I think this means, that the dispense mode is surface, the tip will first “search” for the bottom of the well and then start the dispense in surface mode.
However, it seems to be the case that there is no such option for the MPH and I was wondering why, as it would come in handy in certain situations. It appears to me that dispensing to a surface leads to much cleaner liquid handling compared to the jet mode.


@dominik.b - The touch-off option available in aspiration and dispense steps is only supported by the independent channels. That feature relies on force feedback to determine when the channel is contacting the bottom surface of a well/tube, and the MPH is a significantly heavier tool compared to the channels driven by more powerful motors, making this feature impractical.

That said, touch-off mode does not dictate whether surface or jet mode is used during dispense, rather it is simply another method of using a fixed height dispense relative to the bottom of the well of the labware. When using channels, the touch-off feature can be especially useful when dispensing to various types of labware with varying heights in the same step. When using the MPH, the bottom surface of the labware being dispensed to is uniform in essentially all cases, so the height of the labware surface should be known and conserved.

Surface vs jet dispensing is modulated by the liquid class. You can achieve identical behavior by using a surface empty liquid class with a fixed height. Usually I will opt to not use liquid following, and select an appropriate height depending on the volume being dispensed, so that the end of the tip will self-submerge by the end of the dispense.

Even if touch-off dispense was a supported feature for the MPH, I wouldn’t opt to use it, as the above approach is more efficient - achieving the same end result without spending time seeking the bottom of the labware before beginning the dispense.



Hi Nick,
thank you, this actually makes a lot of sense! I’m off to the lab, measuring the required heights :smiley:

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