1.3.1. The Direct Spectrophotometric Assay
Solutions of nucleic acids strongly absorb ultraviolet light with a max of 260 nm. The intense absorption is due primarily to the presence of aromatic rings in the purine and pyrimidine bases. The concentration of nucleic acid in a solution can be calculated if one knows the value of the solution.
- A solution of dsDNA at a concentration of 50 μg/ml in a 1-cm quartz cuvette will give a reading of about 1.0 at A260.
- A solution of single-stranded DNA that has an A260 of 1.0 in a cuvette with a 1-cm path length has a concentration of about of 33 μg/ml.
- A solution of RNA that has an A260 of 1.0 in a cuvette with a 1-cm path length has a concentration of about of 40 μg/ml.
The spectrophotometric assay for nucleic acids is simple, rapid, nondestructive, and very sensitive; however, it should be noted that it measures both DNA and RNA.