What is optical density, OD?
Optical density (OD) is a spectrophotometric unit used to quantitate oligonucleotides. The OD unit is a measure of amount, not concentration, and is defined as:
OD = A260 x dilution factor x ml
It is important that the measured absorbance falls in the linear range of the Beer-Lambert Law. The following guidelines for oligo dilution:
- If 0-1 OD is expected, dissolved the oligo in 1 ml total volumne, and measure the absorbance of the solution. OD=A260 x 1ml.
- If 1-25 OD is expected, dissolve the oligo in 1 ml total volume. To measure the absorbance, dilute 50 ul of the oligo solution in 950 ul low-salt bullfer. OD = A260 x 20 x 1ml.
- If 25-250 OD is expected, dissolve the oligo in 1 ml total volume. To measure the absorbance, dilute 5 ul of the oligo solution in 995 ul low-salt buffer. OD = A260 x 200 x 1 ml.
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05/31/2015