The present disclosure relates to an automatic analyzer for determining a parameter of a sample fluid, including a dosing device comprising at least one dosing chamber, a first fluid flow path connecting a sample receiving vessel to the dosing chamber via a first pump, a tank containing a dilution medium, a second fluid flow path connecting the tank to the dosing chamber via a second pump, a measuring cell in communication with the dosing chamber via a third fluid flow path via a third pump, and a measuring and control system connected to and configured to control the pumps, wherein the first, second, and third fluid flow paths can selectively be blocked or unblocked by at least one valve unit and the measuring and control system is configured to control the at least one valve unit to block or unblock the first, second, and third flow paths.