Patent ID: 8152900
Filing Date: 2012-04-10
Classification: G01N

Abstract:
1. 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; selecting whether to use a first background absorption data set or a second background absorption data set to determine a measured concentration of the reactive gas in the first sample or the second sample, the selecting comprising selecting one of the first background absorption data set and second background absorption data set having a better correlation with one or more reference absorption characteristics in the second sample absorption data set, the one or more reference absorption characteristics being representative of the first background composition and having no substantial interference from absorption by the reactive gas; generating a differential absorption spectrum by adjusting the second sample absorption data set using the selected one of the first background absorption data set and the second background absorption data set; and converting the 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.