The present invention is one adapted to correct the effect of a second gas component on a first gas component in real time even when the concentration of the second gas component as a coexistent component varies every moment, and includes: a first gas analysis part adapted to measure the concentration of the first gas component contained in sample gas; a second gas analysis part adapted to measure the concentration of the second gas component contained in the sample gas; a correction coefficient storage part adapted to store a correction coefficient for correcting the effect of the second gas component on the first gas component; and a concentration correction part adapted to correct the first gas component concentration on the basis of the correction coefficient, the second gas component concentration of calibration gas used for calibrating the first gas analysis part, and the second gas component concentration.

A system and method for determining impurities in a beverage grade gas such as CO.sub.2 or N.sub.2 relies on FTIR gas analysis for measuring non-sulfur impurities as well as SO.sub.2. CO.sub.2% also can be determined. A multiplexer selects a sample gas from multiple gas samples. Conversion of reduced sulphur present in some impurities to SO.sub.2 is conducted in an oxidizing furnace. Climate control and measurements of oxygen gas impurities also can be provided.

The gas measurement device (1) includes a first detection unit (120) that detects a first component in a sample gas, and a second detection unit (140) that detects a second component and a third component that interfere with the first component. The first detection unit includes a first sample cell (122) and a first detector (10A) which are disposed in series on a first optical path (IR1) of light emitted from a first light source (124). The second detection unit (140) includes a second sample cell (142), a second detector (10B) and a third detector (10C) which are disposed in series on a second optical path (IR2) of light emitted from a second light source (144).

Concentrations of individual hydrocarbons in a gas mixture are determined by measuring absorbance of mid-infrared radiation at specific wavelengths. Computation enables determination of concentrations of individual hydrocarbons despite overlaps of absorption bands.