Chromatographic supports for separation of oligonucleotides

A method of separating oligonucleotides by the steps of entraining the oligonucleotides in a mobile liquid phase and chromatographically subjecting the oligonucleotides to a packing by passing the mobile phase through the packing, the packing comprising inert support particles with a solid silane bonded phase wherein the bonded phase contains (a) a weak anion exchange group consisting of either --(NH)-- or ##STR14## and at least two polar non-ionic groups each within three backbone chain atoms of the weak anion exchange group, (b) contains hydrophobic regions, and (c) the silane surface coverage of the particle is more than about 0.9 micromole/m.sup.2, thereby using both reversed-phase and ion-exchange mechanisms to effect the separation.

A method of formulating a chromatographic packing for chromatographically separating oligonucleotides comprising the steps of:

• reacting a reactive silane with a modifying reagent containing a weak anion exchange group and a polar non-ionic group, to provide a bonded stationary phase, wherein said stationary phase (a) contains a weak anion exchange group consisting of either --(NH)-- or ##STR17## and at least two polar non-ionic groups each within three backbone atoms of the weak anion exchange group and (b) contains hydrophobic regions, and reacting the stationary phase with a support.