Concentration of DNA

David Micklem drm21 at mole.bio.cam.ac.uk
Mon Nov 18 12:13:51 EST 1996


In article <Pine.PMDF.3.91.961118093456.551568441A-100000 at sask.usask.ca>,
fang at SASK.USASK.CA wrote:

>Dear netter,
>How do you measure DNA concentration accurately? By gel (agarose or 
>acrylamide) or by spectrophotometer? What is the lowest concnetration you 
>can get? Say the DNA is 500 - 1 kb in size. How do you measure very low 
>concentration, eg. around 5 ng/ul, and you could not afford 1 ml of DNA 
>sample for measureing? 
>Thank you very much in advance. 
>


Get a 50ul quartz cuvette for your spectrophotometer.  (You usually need an
adaptor to raise it up high enough for the beam).  I never understood why
people buy enormous 1ml (or worse still 3ml) quartz cuvettes when these
tiny ones are available.

Now, lets see, OD260 of 1.0 is about 50ug/ml or 50ng/ul so you won't be
able to dilute your sample much - but might you be able to splurge a whole
50ul?

Alternatively IIRC, there is a way of measuring DNA conc's by photographing
spots containing DNA and ethidium bromide - I think
Maniatis^H^H^H^H^H^HSambrook et al describe it, though it never worked very
well for me.  You need to do a set of standards in parallel every time....

David

_____________________________________________________________
D.R.Micklem,
Wellcome/CRC Institute,       Time flies like an arrow...
Tennis Court Road,              
Cambridge CB2 1QR             Fruit flies like a banana.
UK                             
Tel: [+44] (0)1223 334129     Email:drm21 at mole.bio.cam.ac.uk
Fax: [+44] (0)1223 334089               
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