NDIR apparatus and method for measuring isotopic ratios in gaseous samples
First Claim
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1. An apparatus for measuring the ratio of first and second isotopic species of an analyte molecule in a gaseous sample by non-dispersive IR spectroscopy, comprisingat least one source of IR radiation;
- first and second, interconnected sample cells containing the gaseous sample;
at least one reference cell free of the analyte molecule;
at least one IR detector;
means for providing four optical paths of said radiation impinging on said at least one detector, said optical paths comprisinga first sample path traversing the first sample cell and having a first wavelength range characteristic of the first isotopic species,a first reference path traversing a reference cell and having a first wavelength range characteristic of the first isotopic species,a second sample path traversing the second sample cell and having a second wavelength range characteristic of the second isotopic species, anda second reference path traversing a reference cell and having a second wavelength range characteristic of the second isotopic species;
means for directing radiation through each of said cells;
shutter means effective to permit radiation to traverse each of said paths in rapid succession; and
means for directing radiation from each of said paths onto said at least one detector;
whereby the ratio of said isotopic species is determined by comparison of the intensity of radiation impinging on said at least one detector from said paths.
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Abstract
An apparatus for measuring isotopic ratios provides four separate optical paths for separate measurement of each of two isotopes relative to a reference signal, using spectrally resolved infrared radiation. The design permits the measurements to be made accurately without significant time lags between measurements, and without interchanging of cells or filters.
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23 Claims
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1. An apparatus for measuring the ratio of first and second isotopic species of an analyte molecule in a gaseous sample by non-dispersive IR spectroscopy, comprising
at least one source of IR radiation; -
first and second, interconnected sample cells containing the gaseous sample; at least one reference cell free of the analyte molecule; at least one IR detector; means for providing four optical paths of said radiation impinging on said at least one detector, said optical paths comprising a first sample path traversing the first sample cell and having a first wavelength range characteristic of the first isotopic species, a first reference path traversing a reference cell and having a first wavelength range characteristic of the first isotopic species, a second sample path traversing the second sample cell and having a second wavelength range characteristic of the second isotopic species, and a second reference path traversing a reference cell and having a second wavelength range characteristic of the second isotopic species; means for directing radiation through each of said cells; shutter means effective to permit radiation to traverse each of said paths in rapid succession; and means for directing radiation from each of said paths onto said at least one detector; whereby the ratio of said isotopic species is determined by comparison of the intensity of radiation impinging on said at least one detector from said paths. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 19, 20)
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17. A method for measuring the ratio of first and second isotopic species of an analyte molecule in a gaseous sample by non-dispersive IR spectroscopy, comprising
transmitting IR radiation through four optical paths which impinge on at least one IR detector, said optical paths comprising a first sample path traversing a first sample cell containing the gaseous sample and having a first wavelength range characteristic of the first isotopic species, a first reference path traversing a reference cell free of the analyte molecule and having a first wavelength range characteristic of the first isotopic species, a second sample path traversing a second sample cell, which is interconnected with said first sample cell, and having a second wavelength range characteristic of the second isotopic species, and a second reference path traversing a reference cell free of the analyte molecule and having a second wavelength range characteristic of the second isotopic species; -
determining the concentration of the first isotopic species from the intensity of radiation received at the detector from the first sample path relative to the intensity of radiation received at the detector from the first reference path; determining the concentration of the second isotopic species from the intensity of radiation received at the detector from the second sample path relative to the intensity of radiation received at the detector from the second reference path; and determining from said concentrations the ratio of said isotopic species in the gaseous sample. - View Dependent Claims (18, 21, 22, 23)
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Specification