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Star Republic: Guide for Biologists

Extinction coefficient for oligonucleotide and protein

Extinction coefficient (e) is the absorbance of a 1M solution in a cuvette of 1 cm path-length.

Oligonucleotide measured at A260

e260 ~ 0.89 * ( #A * 15,480 + #C * 7,340 + #G * 11,760 + #T * 8,850 ) (M-1 cm-1)

Protein measured at A280

e280 ~ #Trp * 5,500 + #Tyr * 1,490 + #Cys * 125 /2 (M-1 cm-1)

Here # stands for number of.

To estimate sample concentration, use:

Molar concentration (M) = A / e
or
Concentration (mg/ml) = A / e * Molecular Weight * 1000

For oligonucleotides, replacing # and Molecular Weight with averages, then

Concentration (mg/ml) ~ 30 * A260

For more information and calculators, see BioToolKit.