Patent ID: 7819946

Claim:
A method comprising: collecting a first sample absorption data set for a first sample of a gas mixture that comprises a reactive gas at a reactive gas concentration and a first background composition that contributes spectral interference that hampers direct spectroscopic measurement of the reactive gas concentration in the gas mixture, the collecting comprising passing light from a scannable laser source operating in a scan range through the first sample, the scan range comprising a target wavelength; determining a first measured concentration of the reactive gas in the first sample, the determining of the first measured concentration comprising: selecting a reference spectral peak in the first sample absorption data set, the reference spectral peak being representative of the first background composition and having no substantial interference from absorption by the reactive gas, scaling an unscaled first background absorption data set based on a ratio of the reference spectral peak in the unscaled background absorption data set and the first absorption spectrum to obtain a first background absorption data set, generating a first differential absorption spectrum by adjusting the first sample absorption data set using the first background absorption data set, and converting the first differential absorption spectrum to a first measured concentration of the reactive gas in the gas mixture using calibration data, the first background absorption data set comprising data characteristic of absorption characteristics of the first background composition; selecting whether to use the first background absorption data set or a second background absorption data set to determine a second measured concentration of the reactive gas in a second sample of the gas mixture based on whether a correlation of the first background absorption data set to the first background composition is within a pre-defined tolerance; and determining the second measured concentration by generating a second differential absorption spectrum by adjusting the second sample absorption data set using either the first background absorption data set or the second background absorption data set, and converting the second differential absorption spectrum to the second measured concentration of the reactive gas in the gas mixture using the calibration data.