To determine how much DNA is present in our DNA extractions, we use a neat little machine called a Nanodrop. This tells us how much DNA is present by giving us the absorption spectrums at A260 and A280 Abs. As DNA absorbs ultraviolet, this tells us what concentration of DNA we have.
It also tells us how contaminated our sample is. The ratio of the 260/280 should ideally be between 1.8 and 2. Any lower and there is significant protein contamination, and higher and there's probably lots of salt or something in there.
Or so we thought. And so quite a few of the references and pages seemed to suggest. Until, of course, we got to the Wikipedia article. This tells us, in no uncertain terms, that it takes a relatively large amount of protein contamination to significantly affect the 260:280 ratio, and even provides a little table to show that. It provides a citation link as well, which I can't get to. I've tried Google and Pubmed until I went round in circles, but no one wants to give me that paper. At least not for free :(
So who do we trust? The wikipedia article has a solid-looking table, whereas in most of the other things we read it was just a throwaway line. On the other hand "most of the other things we've read" includes the instruction manual for the machine, which should know what it's talking about. And I have yet to read the wikipedia citation.
On reflection, I think I will disbelieve Wikipedia this time. At any rate, it hardly matters because we still don't actually have any DNA.
Ah well. At least I'm getting paid for it =D
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