The county commission may, when in the commission’s best judgment it is in the best interests of the county, delegate the commission’s procurement authority under this chapter to an individual county department; provided, however, that each instance of single feasible source purchasing authority in excess of five thousand dollars under section 50.783 shall be specifically delegated by the commission. The delegation may allow county departments to negotiate the purchase of services for patients, residents, or clients with funds appropriated for this purpose. In accepting this delegated authority the department acknowledges its ability to, and agrees to, fulfill all of the requirements of this chapter in making purchases and entering into contracts and keeping records. No claim for payment based upon any purchase under this section shall be certified by the commission unless accompanied by such documentation of compliance with the provisions of this chapter as the commission may require. Any department that fails to fulfill all such requirements may have its delegated authority rescinded by the commission. A full and detailed listing of vendors, supplies purchased, and warrants issued for single or multiple source payments shall be retained by the custodian of records.