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Oligos Technical Information
Shelf Life
Lyophilized (-20° C)
Lyophilized (25° C)
Months - Years
Dissolved (-20° C)
6 Months - Year
Dissolved (4° C)
1 week - 2 Months
Storage and Stability
Oligonucleotides are shipped in a lyophilized form. Once the oligonucleotide has been resuspended, it
should be stored at -20° C. If multiple freeze-thaw cycles are anticipated, several aliquots of the
resuspended oligonucleotide should be made prior to freezing. It is suggested to resuspend the
lyophilized oligonucleotide in either sterile water or TE Buffer (10 mM Tris-HCl, 1 mM EDTA, pH 7.5) at a
Quantifying DNA

The quantity of the oligonucleotide may be expressed in terms of A260 units, nanomoles, or
micrograms. The definitions of these units and conversion factors are listed below:  

A260 Units

A260 unit is that quantity of material which, when dissolved in 1.0 milliliter of water and read in a
spectrophotometer at 260 nanometers in a cuvette with a 1 centimeter path, gives an absorbance of

An oligonucleotide with an evenly-distributed base composition which has an absorbance of 1.0 at 260
nanometers has a concentration of approximately 30 microgram/milliliter. The base composition has a
dramatic effect on this approximation, since a sequence of:  
All A's = 20 micrograms/milliliter when A260 = 1.0
All T's = 35 micrograms/ milliliter when A260 = 1.0
All C's = 39 micrograms/ milliliter when A260 = 1.0
All G's = 26 micrograms/ milliliter when A260 = 1.0

Nanomoles (nmoles)

The number of nanomoles of an oligonucleotide is calculated from the measured A260 value using the
millimolar extinction coefficient (mM E260) of the specific oligonucleotide.  
Nanomoles = 1000(Measured A260 value x dilution factor x total volume)/ (E260 of bases + E260 of
The mM E260 values MIDLAND uses are:  
A = 15.1 | G = 11.7 | T = 8.7 | C = 7.4 | I = 6.8  

For example, a 2.0 milliliter sample with the sequence 5'-ATC GAT CGG ATT-3' has a measured A260
value of 0.329 when measured at a 1:11 dilution. The total number of nanomoles in the sample is
calculated as follows:  

Nanomoles = 1000 x 0.329 x 11 x 2.0 / 3(15.1) + 3(11.7) + 4(8.7) + 2(7.4) = 55.7 nanomoles  

Micrograms (mg)

The number of micrograms of oligonucleotide is calculated using the molecular weight (MW) and the
nanomole value (which was calculated from the A260 measurement).  

The molecular weight of the free acid form of DNA can be calculated as follows:  
Enter the number of A's__________ x 313.22 = __________
Enter the number of C's__________ x 289.18 = __________
Enter the number of G's__________ x 329.22 = __________
Enter the number of T's__________ x 304.21 = __________
Enter the mass contribution of any modifications = __________
The molecular weight of the oligonucleotide is = __________
Micrograms (ug) DNA = MW x nanomoles / 1000  

As a general rule of thumb, for an oligonucleotide with an evenly-distributed base composition with
sequence length of 20:  
1 A260 unit = 30 micrograms = 5 nanomoles  
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