How to preserve ground spices?
If you have a chamber vacuum sealer, you could vacuum seal your spices and extend the shelf life. Oxidation is the problem here.  Ground spices are just limited by surface area exposure.  Whole spices, ground as needed, will always be superior.  Your best solutions are to purchase (or grind) small amounts, and use them relatively quickly...or, use a coffee grinder or mortar and pestle to grind whole spices as needed.