The county board of a county with a population of more than one hundred fifty thousand shall and the county board of any other county may employ a purchasing agent who shall not be a county officer of the county. All purchases made from appropriated funds of the county shall be made through the purchasing agent. The county board shall pay the agent for such services during the time of employment as shall be agreed upon at or during the time of employment. The person so employed and designated shall serve at the pleasure of the county board and give bond to the county in such amount as the county board shall prescribe.