From IDT
We recommend briefly centrifuging your oligo tubes prior to opening them, this will ensure the oligo pellet is at the bottom of your tube and will not be lost upon releasing the cap. After you add your TE buffer we would recommend briefly vortexing the tube, but we do not recommend that you spin them down after resuspension.
We recommend dissolving the stock oligo in concentrated form in TE (10mM Tris pH 8.0, 1 mM EDTA). Alternatively, sterile dH2O can be used. DNA kept frozen in a nuclease-free environment should be stable for years. We find it convenient to initially make a freezer stock (which should be thawed relatively infrequently) at 100 uM concentration. To resuspend an oligo at 100 uM concentration, add the volume of TE (in uL) equal to ten times the number of nanomoles of DNA present in the tube (as noted on the spec sheet provided with the oligo) will produce a stock solution at this concentration.
From Tim
I like to keep my freezer stock at 500 uM and then dilute the freezer stock into a working stock of 20 uM which is I what I use on a daily basis. That being said, there's nothing wrong with IDT's method of keeping the freezer stock at 100 uM.