65 ILCS 5/8-10-6
The responsible head of each major department, office, institution, board, commission, agency or instrumentality of such municipal government shall certify in writing to the purchasing agent the names of such officers or employees who shall be exclusively authorized to sign requests for purchase for such respective department, office, institution, board, commission, agency or instrumentality, and all requests for purchase shall be void unless executed by such certified officers or employees and approved by the purchasing agent.
Except as to emergency contracts authorized by Section 8-10-5, no undertaking involving amounts in excess of $10,000 shall be split into parts, by the requisitioning agent or otherwise, so as to produce amounts of $10,000 or less, for the purpose of avoiding the provisions of this Division 10.
The term "responsible head" as used herein shall, in the case of the corporate authorities of the municipality, be such member, members, or committee thereof as shall be designated by appropriate resolution or order adopted by such corporate authorities.
65 ILCS 5/8-10-6