Qubit vs. Nanodrop in clinical lab

[gula]

Hi!
I have to introduce a new analysis in my clinical lab. The test demands a DNA-concentration (after extraction out of FFPET) of 2 ng/µl confirmed with Nanodrop.
I don't have this instrument. We use the Qubit.
I know that the Nanodrop shows higher dsDNA-concentration than Qubit, especially when mixed with other nuclein acids.
Our samples are purified with automated Qiacube technique. So I think contamination with RNA isn't high.

Has anyone made a direct comparison of Qubit and Nanodrop figures in pure dsDNA eluates?

I've found only few figures in internet, that show a huge difference under 1 ng/µl but in higher range a factor of about 1,4.
I have eluates with about 1-150 ng/µl to work with.

thank you in advance for your inputs!
Gula

[mchlbrmn]

I've been using a Nanodrop, and find it very convenient to use. Based on numbers I"ve gotten repeating the same sample, I wouldn't trust it's accuracy below 5 or 10 ng/ul. However, I've not tried to do this so I haven't checked out if there are settings, such as the length of time for the reading, that could be adjusted to improve the accuracy, or if there are other Nanodrops more accurate than my model. I usually take readings of between 50-1000 ng/ul, and it doesn't matter if I'm off by 10%. You might check the manufacturer's specifications to start with.

[gula]

Thanks for your answer.

Do you have directly compared results of nanodrop and qubit of DNA-eluates?

The point is, that the test demands the specified concentration of 2 ng/µl - and that has to be confirmed with nanodrop.
I want to find out a factor for calculation. In other words: what gives a 2 ng-nanodrop-DNA eluate measured in Qubit?

gula

[mchlbrmn]

I have never used Qubit.
In my experience, Nanodrop doesn't measure 2ng/ul accurately. However, as I explained, I do not know for sure whether or not Nanodrops are capable of doing this.

[r.rosati]

I agree, by my experience a Nanodrop isn't reliable at 2 ng/ul.
Nor can similar models - at the moment I use a NanoVue (GE) and it's unreliable below 15-20 ng/ul.

[gula]

After these few months we got both measurement systems now. I made a dilution row of the DNA-eluat (FFPE samples, QIAamp kit), and compared the results of Qubit and Nanodrop. There was no real linearity, but in mean the results of Nanodrop were 2,6 x higher than those of Qubit.
gula