Symptoms:
Stoboscope scheck and automatic dispense setting adjustment will fail with an error message saying that the tip is unstable. In some cases low voltage settings may give stable dispense, but desried voltages result in the errror.
Cause:
Usually the StrobCheck_AdjustDropletSpeedSample.npl program uses multiple passes to measure the current droplet speed, compares this with the desired droplet speed and adjusts the voltage to close the gap between current and desired speed. However, if the deviation between the different passes is too large then the program is interrupted with the “unstable tip” error message. This is because if the tip cannot dispense stably on a constant set of parameters, then it makes no sense to make adjustments.
Solution:
The tip should be cleaned, by using CuvetteCleanerWashMTPStandby.npl with 2 - 3 % Hellmanex. This usually conditions the inner surface of the dispenser and can help stabilise the dispense from the tips.
Further information:
Cleaning needs depend on the application. Some customers need to clean during the pipetting process (extra wash) other not.
Besides malfunctions like a clogged tip or sedimantation inside the nozzle there is the possibility that a tip can become "unstable". The likliehood of this is higher when a tip is not used for longer time. In such a case sometimes the inner surface of the tip becomes hydrophobic often means that the meniscus is not held inside the very front side of the nozzle. If this is the case air bubbles are sucked into the dispenser resulting in instabilities. The cleaning with the cuvette cleaner lowers then surface tension and helps the meniscus to stick at the very front side of the nozzle.