I was wondering what methods people liked to use to verify liquid transfer accuracy within an assay.
During a training course at tecan they used an orange fluorescent dye standard and then analyzed using a plate reader to determine how well an assay moved liquid. I’m curious what other people do
This is probably Tartrazine (Tz), or yellow 5. It’s heavily studied by FDA and as such has well understood absorbances. I believe Artel’s MVS also uses Tz and a second dye for more precise measurements.
I’m currently using this in-lab to QC and calibrate liquid handling on my Biomek since their PM service does not include any sort of volume verification. The general idea is you can measure the dye in solution, and the absorbance reading is proportional to the quantity of Tz in solution. A few conversions later and you can figure out the volume of the original aliquot assuming you know the concentration of the stock solution prior to transfer.
Caveats: It is a measurement of the entire system from Tz purity to stock preparation to liquid handling to spectrometer. It’s best to combine multiple techniques if you can, or at least verify the results orthogonally. Also it really sucks if your liquid handler’s components are only replaced on an “as-needed” basis rather than preventative so CV could really effect your results (thanks again biomek “PM” service)
Checking Dispensing Volume
Already contains some good discussion on this.
I really liked the link to ISO 23783-2:2022
The two places I have worked at have both used Orange G with a balance or at my old job compared against a handheld validated pippet.
As @evwolfson noted, it was definitely Tartrazine or Orange G. I’ve heard people also prefer a specific kind of blue ink but I hope that I am never in the weeds that much tbh.
Tecan also uses Artel kits in the field which are worth every penny in regulated worlds.
With that said, you can’t go wrong with a good scale and some basic density calculations. It’s actually incredibly easy to create closed loop systems for this kind of liquid class work but it only gets you so far, doesn’t really say much about the context of the action (speeds, retraction, delays, etc…) Hitting your accuracy/precision # is like 10% of the work in my experience.
Unless they changed the formulation in the last few years, the Artel system uses a mixture of Copper Sulfate and Ponceau S. The Copper Sulfate is provided at a static concentration in the test solution and diluent while the Ponceau is only in the test solution.