I also like our Nanodrop, but I do not recommend using it for Bradford 

The 25% accuracy mentioned by Flip is pretty good for biological samples.  
Using 50 ul cuvette in a traditional spectrophotometer will not give this 
accuracy because cleanness of the cuvette will be a big issue...


On Jun 16, 2011, at 12:43 PM, Oganesyan, Vaheh wrote:

> I completely disagree with Filip’s assessment. I’ve been using nanodrop 
> nearly 5 years and never had inconsistency issues. If you work at reasonable 
> speed (if you put a drop there then lower the lever and click measure before 
> you do anything else) there will be no issues. At very high concentrations 
> the accuracy and therefore consistency may become lower. Concentrations 
> between 5 and 10 mg/ml should be fine. The instrument is pricey though.
>      Vaheh 
> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Filip 
> Van Petegem
> Sent: Thursday, June 16, 2011 3:34 PM
> Subject: Re: [ccp4bb] Nanodrop versus Nanophotomter Pearl versus good old 
> Bradford.
> Dear Arnon,
> the Bradford method is not recommended for accurate measurements.  The 
> readings are strongly dependent on the amino acid composition.  A much better 
> method is using the absorption at 280nm under denaturing conditions (6M 
> Guanidine), and using calculated extinction coefficients based on the 
> composition of mostly Tyrosine and Tryptophan residues (+ disulfide bonds).  
> This method is also old (Edelhoch, 1967), but very reliable.
> One thing about the nanodrop: smaller volume = more evaporation.  On the demo 
> we've had, I was so unimpressed with the precision (>25% variability between 
> two consecutive measurement) that we didn't consider this instrument at all.  
> So unless you just want a 'rough' estimate, I wouldn't recommend it at all. 
> But most respectable spectrophotometers will take cuvettes with 50ul volumes 
> - a big step up from 1ml volumes...
> Filip Van Petegem
> On Thu, Jun 16, 2011 at 12:15 PM, Arnon Lavie <la...@uic.edu> wrote:
> Dear fellow crystallographers - a question about spectrophotometers for 
> protein concentration determination.
> We are so last millennium - using Bradford reagent/ 1 ml cuvette for protein 
> conc. determination.
> We have been considering buying a Nanodrop machine (small volume, no dilution 
> needed, fast, easy).
> However, while testing our samples using a colleague's machine, we have 
> gotten readings up to 100% different to our Bradford assay (all fully 
> purified proteins). For example, Bradford says 6 mg/ml, Nanodrop 3 mg/ml. So 
> while it is fun/easy to use the Nanodrop, I am not sure how reliable are the 
> measurements (your thoughts?).
> So QUESTION 1: What are people's experience regarding the correlation between 
> Nanodrop and Bradford?
> While researching the Nanodrop machine, I heard about the Implen 
> NanoPhotmeter Pearl.
> So Question 2: Is the Pearl better/worse/same as the Nanodrop for our purpose?
> Thank you for helping us to advance to the next millennium, even if it is 
> nearly a dozen years late.
> Arnon
> -- 
> ***********************************************************
> Arnon Lavie, Professor
> Dept. of Biochemistry and Molecular Genetics
> University of Illinois at Chicago
> 900 S. Ashland Ave.
> Molecular Biology Research Building, Room 1108 (M/C 669)
> Chicago, IL 60607
> U.S.A.
>                             Tel:        (312) 355-5029
>                             Fax:        (312) 355-4535
>                             E-mail:     la...@uic.edu
>                             http://www.uic.edu/labs/lavie/
> ***********************************************************
> -- 
> Filip Van Petegem, PhD
> Assistant Professor
> The University of British Columbia
> Dept. of Biochemistry and Molecular Biology
> 2350 Health Sciences Mall - Rm 2.356
> Vancouver, V6T 1Z3
> phone: +1 604 827 4267
> email: filip.vanpete...@gmail.com
> http://crg.ubc.ca/VanPetegem/
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