A gas chromatograph in which components of a sample of a gas mixture are separated via a separation column, a sensing element of a thermal conductivity detector is operated at a first temperature to detect separated components and to generate a detector signal in response to detected components, an evaluation unit evaluates detector signals and determines concentrations of detected components, a further sensing element of a further thermal conductivity detector is operated at a second temperature different from the first temperature, to detect gas components of widely different concentration ranges at high sensitivity, where the thermal conductivity detectors are calibrated for different concentration ranges, and the evaluation unit compares the detector signal with the detector signal of the further thermal conductivity detector to output a concentration value determined from the signal of the thermal conductivity detector calibrated for the measured component concentration.