Variation between spectros - tot RNA concentrations (Nov/04/2009 )

Hi, I was wondering if somebody could give me an idea as to what sort of variation could be considered "acceptable" for total RNA concentrations.

Basically, i extracted insect total RNA a few months ago, concentration at the time (measured with nanodrop) was about 700ng/ul, subsequent work using these samples have worked perfectly.

We have recently purchased a spectro that measures samples inside the pipette tip - sounds good, but i´m having trouble validating the concentrations. Using the samples mentioned above (7mths old, thawed/frozen a couple of times) i get concs of about 550ng/ul. i checked on the nanodrop, and there the values vary by about +/- 20ng/ul.

Gut instinct tells me 150ng/ul difference between spectros isn´t good, but many people here won´t do repeat measurements on their spectros, because they always give different values. its more important to use the same spectro/system for everything...

How much is too much?

hi there.. there can be variations between various specs based on its mode of detection (here as u say), the monochromator system, etc. So teh variation can range from 5% to 15-20% in some cases. But as a thumb rule, concentration variations, if less than 10% are considered good. As conc decreases, teh variation in amount will not be seenas a big difference, but in percentage, you will come to know the real variation.
Best luck.