Although the path length of NanoDrop is fixed. 1 ul may not form good liquid
column. One trick is to spot a little bit more sample, 2-4 ul, on Nanodrop,
specially for concentrated protein samples with glycerol and E. coli
culture. It eliminate the bubble problem. 

To get good reading, a new drop need to be used for each measurement. The
liquid column may not form well when repeat with the same drop. Take a look
at the liquid column. Nanodrop actually measures the sample twice for each
reading. In consistent measurements give error message. As all the machines
with moving parts, periodical maintenance is needed to give good readings.

There may be a huge difference between Bradford and A200. In some cases none
of them gives the true concentration. I wouldn't abandon Bradford, which by
itself is very consistent if done right. Indicating how protein
concentration is measured in publications will help the research community.



-----Original Message-----
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Bjørn
Panyella Pedersen
Sent: Thursday, June 16, 2011 1:19 PM
Subject: Re: [ccp4bb] Nanodrop versus Nanophotomter Pearl versus good old

On 2011-06-16 13:06, Filip Van Petegem wrote:
> Even if evaporation is not an issue, one has to take pipetting errors into
> when dealing with small volumes.  The relative error on 1-2ul is a lot
bigger than on 50ul.

True, but the nanodrop works independent of volumes, since it has a 
fixed pathlength.  1ul loaded will give the same result as 2ul loaded.

Bjørn Panyella Pedersen
Macromolecular Structure Group
Dept. of Biochemistry and Biophysics
University of California, San Francisco

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