For long-term storage we recommend that the oligos be dissolved in a buffer, such as TE (10 mM Tri-HCl, 1 mM EDTA, pH 8.0), instead of just sterilized water. Once resuspended, oligos should be kept frozen at -20°C. Since some oligos may not be easily dissolve in sterilized water the addition of NaOH does help dissolve oligos in water.
Normally, oligos should be stable at -20°C and can be stored at that temperature for more than a year. Although stable in solution, oligos will be degrade if the storage solution is contaminated with nucleases. Therefore, we recommend that oligos be stored in the dried form. If you want to store oligos in solution, it is best to aliquot the oligo into several tubes and store them separately. Oligos can also be subject to degradation due to the 'Freezing and Thawing Effect' when the oligo solutions are frozen and thawed repeatedly. For storage of oligodeoxyribonucleotide (DNA), pH value should be maintained at neutrality. Under acidic conditions, DNA can become depurinated. On the other hand, the phosphodiester bond of oligoribonucleotides (RNA) can be hydrolyzed under basic conditions.