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. <EOS>