Precision Trace Gas Analysis by FT-IR Spectroscopy. 1. Simultaneous Analysis of CO2, CH4, N2O, and CO in Air

We report the development of a method of trace gas analysis based on 1-cm-1 resolution Fourier transform infrared (FT-IR) spectroscopy, deployable in both laboratory and field applications. Carbon dioxide, methane, nitrous oxide, and carbon monoxide may be analyzed simultaneously in a single air sample using this method. We have demonstrated that the method can provide analytical precision of the order of ±0.15 μmol mol-1 for CO2, ±0.9 nmol mol-1 for CH4, ±0.3 nmol mol-1 for N2O, and ±0.3 nmol mol-1 for CO, expressed as mole fractions in dry air. The analytical precision is in all cases competitive with or superior to that of the more usual methods of analysis for these trace gases, namely, nondispersive infrared spectroscopy for CO2 and gas chromatography-based techniques for CH4, N2O, and CO. The novel FT-IR method relies on calibration using synthetically calculated absorbance spectra and a chemometric multivariate calibration algorithm, classical least squares.