A method for gas concentration measurement, the method comprising: - guiding a liquid sample into a bellows piston, - extracting a gas or gas mixture dissolved in the liquid sample from the liquid sample using an extraction system, wherein the extraction system comprises a bellows piston for fluid sampling, gas extraction by vacuum and subsequent gas compression, and a linear motor for operation of the bellows piston, and wherein the extraction system is configured to extract the gas or gas mixture from the liquid by vacuum combined with agitation of the liquid, - compressing the gas or gas mixture using the linear motor for operation of the bellows piston, - conducting the gas or gas mixture into a measurement chamber, - generating a measurement signal by a radiant source, - directing the measurement signal to the gas or gas mixture to be measured in the measurement chamber, - modifying the measurement signal by a filter or a wavelength dispersive element in order to enable the observation of the wavelength dependence of the signal intensity, - detecting the modified signal by a detector or a detector matrix, - measuring the signal intensity as a function of the wavelength at at least two wavelengths at a first pressure, - varying the pressure to a second pressure by moving the bellows piston connected to the measurement chamber, - measuring the signal intensity as a function of the wavelength at at least two wavelengths at the second pressure, - generating a zero signal intensity by mathematical extrapolation of the measured signal intensities to zero pressure (P 0), and - subtracting an offset of the zero signal intensity from offsets of the measured signal intensities. - guiding a liquid sample into a bellows piston, - extracting a gas or gas mixture dissolved in the liquid sample from the liquid sample using an extraction system, wherein the extraction system comprises a bellows piston for fluid sampling, gas extraction by vacuum and subsequent gas compression, and a linear motor for operation of the bellows piston, and wherein the extraction system is configured to extract the gas or gas mixture from the liquid by vacuum combined with agitation of the liquid, - compressing the gas or gas mixture using the linear motor for operation of the bellows piston, - conducting the gas or gas mixture into a measurement chamber, - generating a measurement signal by a radiant source, - directing the measurement signal to the gas or gas mixture to be measured in the measurement chamber, - modifying the measurement signal by a filter or a wavelength dispersive element in order to enable the observation of the wavelength dependence of the signal intensity, - detecting the modified signal by a detector or a detector matrix, - measuring the signal intensity as a function of the wavelength at at least two wavelengths at a first pressure, - varying the pressure to a second pressure by moving the bellows piston connected to the measurement chamber, - measuring the signal intensity as a function of the wavelength at at least two wavelengths at the second pressure, - generating a zero signal intensity by mathematical extrapolation of the measured signal intensities to zero pressure (P 0), and - subtracting an offset of the zero signal intensity from offsets of the measured signal intensities.