A method includes receiving a gas mixture at a first pressure including at least a primary gas and a secondary gas and changing a pressure of the received gas mixture from the first pressure to a second pressure. Further, the method includes determining a spectra of the gas mixture at the second pressure, wherein at least the first spectral line of the primary gas is spectrally distinguished from at least the second spectral line of the secondary gas, identifying a peak wavelength associated with the spectrally distinguished first spectral line of the primary gas based on at least two wavelengths of the secondary gas corresponding to at least two peak amplitudes in the spectra of the gas mixture, and determining a concentration of the primary gas based on the identified peak wavelength associated with the spectrally distinguished first spectral line of the primary gas.