Method of monitoring operation of detection of analyte in liquid sample

The invention relates to a method of monitoring an operation of detection of an analyte in a liquid sample using a measuring cell (108), the measuring cell (108) comprising a working electrode (120) for excitation of electro-chemiluminescence in the liquid sample, an optical detector (126) for detecting the excited electro-chemiluminescence, the excitation and detection being performed in an electro-chemiluminescence measurement cycle, the measurement cycle comprising transporting the liquid sample via a transport path (114) to the working electrode (120) using a support liquid, the method comprising: coupling light of a light source (204) into the transport path (114) during part of the measurement cycle, the transport path (114) forming a light guide between the light source (204) and the optical detector (126), detecting the coupled light by the optical detector (126), analyzing the detected light regarding the presence of a gas bubble (214) in the transport path (114), providing ameasurement state in case