Checking Dispensing Volume

The few places I’ve worked we’ve integrated the Sartorius Entris line of balances onto work cells, often times HTS systems and weigh after every liquid handling step. You won’t pick up well to well variation, but you catch the majority of tips clogs for bulk dispensers, issues with running out of a reagent, drift over time (highly dependent on the mechanism of the liquid handler/bulk dispenser), etc. In some situations when the liquid handler/bulk dispenser volume can be controlled by a variable or worklist we’ve enabled feedback control of the instruments with the balances. The monitoring with the balances has been incorporated into GNF Systems’ Director software, Wako’s Director (i think), GBG, SAMI and Momentum. Each weigh step you can specify thresholds and warnings or errors on out-of-range conditions. This has been in posters and talks from GNF many years ago, but is still very underutilized in my opinion. These balances cost ~$1100, so one of the least expensive devices on most workcells, and the weigh step is only a couple seconds, usually it boils down to the speed of the system/robot whether it becomes a drag on the throughput and in that case we’d opt to weigh plates on some interval, such as every 5th plate. The interesting thing once you start looking is that just about every dispenser drifts over time, the degree of that drift is highly variable depending on the reagent and the mechanism of the dispenser. It’s eye opening!

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Hello Oleksandr,
You can have a look at this tool:
[Discngine Qualification - A Web Application To Track Liquid Handling Precision and Accuracy - Home] Discngine Qualification
Perhaps you will find some feaures you are looking for.

Which dispenser were you working with?

GNF Systems’ WDII in all the schedulers I mentioned. It can take a method with a Correction Factor to scale the volume. Also done on a multidrop Combi in GBG. In that one the Combi can be run a few different ways, in one you call a method, another you specify a few parameters including the volume. Really, any dispenser where the volume can be a variable or it runs off a worklist (ie Combi nL) you can scale the volume/worklist with a script or logic built in to you scheduler method if in the scheduler you can define variables (preweight, postweight, density, numWells and empty plate weight is nice if you want to capture residual volumes) and operators (-+/x). One thing to be mindful of is density and numWells can be global variables and all the weights should be variables attached (unique) for each plate. The devices where you just call a method defined on that instrument are mainly the ones we can’t enable feedback control, but we still weigh before/after to capture drift, clogs, etc.

We’ve also used weigh steps after incubation periods to monitor evaporation and determine if lids are necessary. And before/after pipettors like the Bravo or FLIPR, any liquid handling step. Again, important to note for the pipettors you likely are not going to pick up a few tips that are over/under dispensing, but you may capture interesting patterns like if you reuse a tip box for several plates how the first transfer differs compared to all the other transfers after the tips have been wetted (something that can be accounted for using conditioning volume or a premix step to wet the tips).