Per-frequency spectroscopic interference correction
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Solution Overview
Problem
Existing gas phase chemical analysis methods using absorption spectroscopy face challenges in accurately quantifying gas concentrations due to systematic errors known as crosstalk, which occur when multiple compounds are present and their absorption spectra do not match the model functions.
Innovation Solution
A novel approach to crosstalk correction involves directly correcting the input spectra prior to fitting, using per-frequency crosstalk correction factors based on Taylor expansions of the measured absorption at each frequency, allowing for flexible changes in spectral scans and optimization parameters without affecting the efficacy of the crosstalk correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional least-squares fitting is used to analyze absorption spectra, then the analysis process is simple and computationally efficient, but systematic errors known as crosstalk occur when multiple compounds are present and their absorption spectra do not match the model functions
Solution Approach 1:
The patent applies preliminary action by correcting the absorption spectrum before the fitting process. Correction factors are calculated based on the measured spectrum and applied to remove interfering absorptions from other compounds. This pre-correction step eliminates crosstalk errors before the least-squares fitting is performed, allowing simple computational methods to achieve high measurement precision.
2Ease of operation
If model functions are used for spectral analysis, then the quantification process is straightforward, but errors in the model functions lead to crosstalk between different gas species measurements
Solution Approach 1:
The patent implements feedback by using the measured absorption spectrum itself to calculate correction factors. The correction factors are derived from the actual measured spectrum and the known model functions, creating a feedback loop that adapts to the specific sample being analyzed. This feedback mechanism compensates for model function inaccuracies and eliminates crosstalk while maintaining quantification simplicity.
3Measurement precision
If per-frequency correction factors are calculated and applied to the absorption spectrum, then crosstalk errors are effectively reduced, but additional computational steps are required
Solution Approach 1:
The patent applies parameter changes by transforming the correction approach from a global fit parameter modification to a local per-frequency correction. Correction factors are calculated for each frequency point based on the measured absorption and model functions. This parameter transformation allows precise crosstalk removal at each frequency while maintaining a relatively simple overall computational structure that can be efficiently implemented.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces crosstalk errors by correcting absorption spectra on a per-frequency basis before fitting, enabling accurate gas concentration measurements even when spectral scans or optimization parameters change, and is particularly beneficial for measuring trace levels of volatile organic compounds in ambient air.
Implementation Method 1
gas phase chemical analysis using absorption spectroscopy
Implementation Method 2
The least squares optimization will attempt to distribute the error in the one model function among the reported concentrations of the other compound, in such a way that the overall data-model mismatch is minimized. For example, for a gas sample containing two gases, CO2 and NH3
Data Source
AI summary
Improved correction of optical absorption spectroscopy results for trace gas detection is provided by correcting for species crosstalk (and other environmental effects) on a per-frequency basis. Analyte concentrations are then determined by curve fitting to the corrected absorption spectrum. This is in marked contrast to the conventional approach of first performing a curve fit to determine analyte concentrations, then correcting the analyte concentrations to account for species crosstalk and other environmental effects. In some embodiments, the number of parameters for the per-frequency corrections are automatically determined from the data (e.g., using a LASSO regression).