We have troubles with our Qubit BR assay. We sent samples for sequencing twice and 2 independent sequencing companies replied that the samples were 5 and 6 times more diluted than we told them. This means that that our quibit somehow overestimates DNA concentration. However, it measures accuratelly the BR standard 2 (lambda DNA 100ng/ul) when measured as a sample. It is rather enigmatic. I tried to measure different DNA of known concentration and used gene ruler DNA ladder mix (fermentas) that should be 500ng/ul. The quibit measured 1300ng/ul, which is almost 3 times more than it should be. Then I measured BR standard 2 (it should be 100ng/ul) again and the measurement was accurate = 100ng/ul . Any ideas whats wrong?
Hello Tomas,
My first thought is..., don't trust your standard. Perhaps better to buy a new set of standards for Qubit.
Maybe someone unintentionally diluted it.
Also you might try a simple serial dilution of known DNA concentration sample and assess your SOP for measuring DNA concentration.
Best of luck.
After your initial Qubit reading did you input the amount of sample (ul) that is in your tube?
Sebastijan Hobor
I think that qubit check standart concentration during calibration. So if the marker 2 would not be 100ng/ul, quibit could not be calibrated.
I also have problems with gDNA quantification. The same samples were measured in 2015, 2016 and 2017 (kept at -20°C), and I got respectively 3.5, 12.0 and 45 ng/µL! I used the Qubit dsDNA HS kit.
This is also enigmatic for me!
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