When the DNA or RNA sample concentration is approximately 20 ng/uL or less, the purity ratios are unreliable.
Purity ratio of DNA and RNA is measured by the ratio of absorbance at 260 nm and 280nm. A ratio of ~1.8 is generally accepted as pure for DNA, while that for RNA is ~2.0. Presence of protein, phenol or other contaminants can make the ratio appreciably lower. Also to ensure you get accurate result purification prior to measurement is necessary.
Yes, you can't rely on this concentration. For miRNA or other small RNA could be once considered but not mRNA. Either you go for fresh isolation or in rare cases, you can try 100ng cDNA synthesis. But that will depend on how much volume of RNA you have. Could you please share A260/280 and A260/230 reading??
Purity ratio of DNA and RNA is measured by the ratio of absorbance at 260 nm and 280nm. A ratio of ~1.8 is generally accepted as pure for DNA, while that for RNA is ~2.0. Presence of protein, phenol or other contaminants can make the ratio appreciably lower. Also to ensure you get accurate result purification prior to measurement is necessary.
To add a few details, the A260 indicates quantity/concentration, while the A280 and A230 indicate purity.
A280 measures mostly protein contamination, and A230 contamination by organic compounds.
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