260/280 ratio larger than 2.0 - (Aug/22/2008 )
what do the values imply if 260/280 of my RNA samples are larger than 2.0? (sample 1: 2.07 , sample 2: 1.98 , sample 3: 2.04, sample 4: 1.96, sample 5: 2.09)
it seems that the whole set of samples have a pretty high 260/280 ratios and it is the first time for me to have readings larger than 2.0.
do anyone know why?
it seems that the whole set of samples have a pretty high 260/280 ratios and it is the first time for me to have readings larger than 2.0.
do anyone know why?
In a broad sense, >2.0 values suggest that your nucleic acid sample is generally not degraded. The nasty caveat is that this gives you no possible way of excluding the possibility that there is DNA contamination in your RNA. You could try running it on an Agilent Bioanalyzer RNA chip or run an agarose gel to do a further QC check. I often face your situation, and that's what I do.
i use a lot of time surfing the net, but there are no explanations for the reason why the ratio is greater than 2.0. anyway thx for your reply. by the way, if i use agarose gel as a QC checker , what will the result look like in case of DNA contamination?
You'd have to go back to Warburg, O. and W. Christian. 1942. Isolierung und Kristallisation des Gärungsferments Enolase. Biochem. Z. 310:384–421 to find out... 
The method was originally designed to indicate the degree of nucleic acid contamination in protein preparations.
A260/280 ratios are not something I do routinely (can't recall the last time I bothered) and I've never been hung up on it, but it is one of those things that some people do lose sleep over. I have, on the other hand, checked my RNA quality on an Agilent bioanalyzer in preparing for genechips.
See here.
There are too many thing can affect 260/280 ratio.
For example using TE disolve RNA can get relatively high 260/280 compare juct using DEPC-water.
I only check is ratio below 1.5 (that is just my standard), and if below 1.5 I will do additional clean up.
When above 1.5, I won't spand my time to evaluate how high the ratio goes, just go to next step checking RNA quality in agarose gel.
In case of DNA contamination, first thing you will notice is very large molecular weight band(s) appear (in many of my case above 5000 bp).
In my opinion, the contamination is not DNA maybe other things ,when I tried digestion with DNAase I , I still sometimes collected a higher ratio of 260/280 after repurification with phenol chloroform, but that doesnot hold back to the next steps (RT-PCR) for me
it seems that the whole set of samples have a pretty high 260/280 ratios and it is the first time for me to have readings larger than 2.0.
do anyone know why?
Maybe there are many factors to influence it, and in my case residual alcohols resulted in high 260/280 values. I guess higher 260/280 ratio does not influence concentration determination..(maybe i hope so
)By the way does anybody know the meaning of 260/230 ration for RNA? Some peaple think this is important also.