Using a Procurment category into Purchase workflow

Hi , How can I setup a PO workflow where the requester belongs to a certain department and he is submitting a PO with a procurement category which is part of category hierarchy ? I;e John request a PO for amounts of 500K to buy Office supplies ( part of category General Supplies) and the PO must be approved by John’s manager.

I’m not able to see how I can use Managerail hierarchy with procurement categories in the same workflow with approval & spending amounts. Any help will be appreciated. Thanks