What is NanoDrop?
NanoDrop spectrophotometer is used to measure DNA, RNA or protein concentration and its purity. It can be used to measure absorbance spectra or single wavelengths of the sample. However, you can't determine DNA or RNA integrity with this. You can determine DNA or RNA integrity with 1% agarose gel electrophoresis.
Detection wavelengths for the components
230 nm: carbohydrates, phenol, guanidine HCl, EDTA
260 nm: nucleotides, RNA, ssDNA, dsDNA
280 nm: protein, phenol, other contaminants
Thus, the ratio of absorbance at 260 nm and 280 nm is used to check nucleic acid/protein ratio. And the ratio of absorbance at 260 nm and 230 nm is used to check nucleic acid/organic compounds.
260/280
The 260/280 ratio of ~1.8 is accepted as pure for DNA; the ratio of ~2.0 is accepted as pure for RNA. If the ratio is lower than expected, it may indicate the presence of protein. The ideal 260/280 ratio of common proteins is 0.6. If the value is higher than expected, it may indicate the contamination of nucleic acid.
The reason RNA has a higher ratio is because of Uracil. Uracil has a higher 260/280 ratio than the ratio of Thymine.
260/230
The 260/230 ratio of 2.0-2.2 is accepted as pure for nucleic acid. If the value is lower than expected, it may indicate the presence of organic compounds such as carbohydrates, phenol, guanidine HCl and EDTA.
Note
If the ratio value is too low, you should do nucleic acid purification.
If the ratio value is too high, it may indicate poor blank quality.
You may get inaccurate ratio value at very low concentration (< 10 ng/ul) of nucleic acids.
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