big difference between two RNA quality test? - (Feb/24/2005 )

I used bioanalyzer and spectrometer to test my RNA extracted from the human blood. There is big difference between them. The 260/280 ratio got from spec is 2.0 (which is OK for microarry), but the bioanalyzer shows the 28s/18s ratio is 0.9!! (although the concentration test by both methods is consistent) Actually I dilute the sample from 500 to 200ng/ul with elution solution before bioanalyzing.

Does anybody know how can the results be so different? Thank you!

hi

For checking the purity of nuclec acid preps, ratio 260/280 (regarding proteins) or 260/230 (regarding aromatics) should be greater than 1.8.

But an additionnal test is measuring the ratio 28S/18S. Normally, there is 2fold 28S than 18S. It's usually used (as i know but correct me if i'm wrong) to measure the degradation of your RNA. If it occurs, this ratio is different to 2:1. In your experiment, it seems that partial degradation occured.
Did you check your prep on agarose formaldehyde gel?

Fred

Thank u. Fred. I c.

The gel image is provided by the bioanalyzer people. 2 bands shown, upper one is dimmer than the lower one.

What can cause the degration? Will the salts influence the peak of 28s(some one told me)? Do you konw if the elution solution contain salts?