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Quantifying DNA 1

Quantifying DNA 1 — Absorbance to Concentration

 
Calculate the concentration of nucleic acid in the original solution of either double-stranded DNA (dsDNA) or single-stranded oligodeoxynucleotide (oligo) from the absorbance at 260 nm of a diluted sample, measured in a spectrophotometer.
[dsDNA: 1 A260 ≡ 50 µg/ml]
[oligo: 1 A260 ≡ 33 µg/ml]

Original concentration: µg/µl   
 
You should aim to do these calculations in your head or on a scrap of paper (i.e. without a calculator). The following logic may be helpful:
  • The concentration of the diluted solution (µg/ml) is the measured A260 multiplied by 50 (dsDNA) or 33 (oligo).
  • This must then be multiplied by the dilution factor to give the concentration of the original solution (µg/ml).
  • This is divided by 1000 to convert from µg/ml to µg/µl.
  • The concentration of the original solution is therefore:
    Absorbance x (50 or 33) x dilution ÷ 1000
Always do a ‘sanity check’ on your answer. Is it the right order of magnitude? Be suspicious of very high or very low values.