Posted on May 16th, 2016 by UNM CC
The Nanodrop will display an absorbance spectrum for each sample as it is being measured. DNA should have an absorbance peak centered at a wavelength of 260 nm (A260). The ratio A260/A280 should be ~1.95. The presence of organic solvents (e.g. phenol) may lead to a spuriously high A260/A280 ratio (> 2). Proteins will have a peak absorbance at 280 nm, so protein contamination will lower the A260/A280 ratio. Protein does not absorb as strongly as DNA so even a modest reduction in the A260/A280 ratio (e.g. 1.8) may represent a high level of contamination. The extinction coefficient is a factor that converts the peak absorbance to concentration. For DNA the extinction coefficient is 50 (ng/µL DNA) / A260. The nanodrop has a broad linear range. Accuracy drops off (error > 10%) for concentrations < 4 ng/µL and > 4000 ng/µL.
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