[DIYbio] Expected accuracy of UV spectrophotomers

Hi,


I'm wondering what the expected accuracy of UV spectrophotometers are when quantifying dsDNA. I had DNA in TE which I believed was 100 mg/ml based on resuspending a known quantity of DNA as measured by a synthesis company. I dilluted it 50x to a total volume of 100ul and measured in two different spectrophotometers.

Spec 1 (Thermo Electron Helios Gamma):
A260 = 0.031 A
A280 = 0.019 A
Calculated concentration: 77.5 ug/ml

Spec 2 (Eppendorf BioPhotometer):
A260 = 0.050 A
A280 = 0.022 A
Calculated concentration: 125 ug/ml

The consistency was a little disappointing. Is this normal or do you think there is a problem with my specs? I suppose I could get more accuracy by diluting less but I hate using up so much plasmid just for quantification.

-Josh

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