(1) Purchase Orders. All purchases, except those made under contract, shall be made only after issuance of a purchase order by the purchasing officer and no invoice shall be approved for payment unless authorized by such an order.

(2) Spot Purchase Order. Purchases not exceeding $25.00 may be made by those authorized by the purchasing officer but only upon issuance of a spot purchase order in writing signed by the authorized officer. A copy of such spot purchase order must be delivered to the purchasing officer within 24 hours, weekend and holidays excepted.

(3) Appropriation Required. The purchasing officer shall issue a purchase order only if there is an appropriation sufficient for the purchase and for other anticipated or budgeted purposes. [Code 1975 § 1-1.0412.]