Patent ID: 8500849

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 tunable or scannable laser light source operating in a scan range through at least part of the first sample such that the light reaches a detector after passing through the at least part of the first sample, the first sample absorption data set comprising a test harmonic absorption curve having a test curve shape; retrieving, by a computer processor, a reference harmonic absorption curve of a laser absorption spectrometer comprising the tunable or scannable laser light source and the detector, the reference harmonic absorption curve having a reference curve shape and comprising a first, a second, or a higher order harmonic signal of a reference signal generated by the detector in response to light passing from the laser light source through a reference gas or gas mixture, the reference gas or gas mixture comprising one or more of the reactive gas and the background composition; the reference harmonic absorption curve having been determined for the laser absorption spectrometer in a known or calibrated state; comparing the test harmonic absorption curve with the reference harmonic absorption curve to detect a difference between the test curve shape and the reference curve shape that exceeds a predefined allowed deviation and therefore indicates a change in an output of the laser light source relative to the known or calibrated state; adjusting one or more operating and/or analytical parameters of the laser absorption spectrometer to reduce the difference between the test curve shape and the reference curve shape; collecting a second sample absorption data set for the first sample or a second sample using the adjusted one or more operating and/or analytical parameters; generating a differential absorption spectrum by adjusting the second sample absorption data set using a background absorption data set comprising data characteristic of absorption characteristics of the first background composition; and converting the first differential absorption spectrum to a first measured concentration of the reactive gas in the gas mixture using calibration data.