Method and apparatus for chemical analysis
First Claim
1. The method of determining a measure of absorbance of electromagnetic energy per unit path length by chemical species within a medium that scatters and absorbs electromagnetic energy, comprising the steps ofirradiating the medium with electromagnetic energy containing at least two components of different frequency, at least one of which is amplitude modulated;
- detecting electromagnetic energy emerging from said medium;
measuring the intensity of the detected energy at each of said frequencies and comparing it to a measure of the irradiating intensity at each of said frequencies to provide a measure of absorbance of said energy at said different frequencies;
determining from said at least one amplitude modulated component of the electromagnetic energy information relating to the path length travelled by said component; and
deducing, from the measure of absorbance and the information relating to the path length travelled, a measure of absorbance per unit path length travelled by the radiation for each of said frequencies.
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Abstract
A method and apparatus for determining the presence of an analyte in a medium or the composition of a medium wherein a volume of material is irradiated with temporally-modulated electromagnetic energy at multiple wavelengths. The electromagnetic radiation is detected after it has traversed a portion of the material. Representation signals related to the degree of absorption of electromagnetic energy at various wavelengths in the material and signals related to the path lengths travelled by the electromagnetic radiation in the material are generated, and signals representative of the optical absorption per unit path length at various wavelengths in the medium are derived. The derived wavelength dependence of the optical absorption per unit path length is compared with a calibration model, and the comparison is analyzed to derive concentrations of specific chemical species within the material and the presence of an analyte or composition of the medium. An output indicative of the concentration and composition is then provided.
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Citations
44 Claims
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1. The method of determining a measure of absorbance of electromagnetic energy per unit path length by chemical species within a medium that scatters and absorbs electromagnetic energy, comprising the steps of
irradiating the medium with electromagnetic energy containing at least two components of different frequency, at least one of which is amplitude modulated; -
detecting electromagnetic energy emerging from said medium; measuring the intensity of the detected energy at each of said frequencies and comparing it to a measure of the irradiating intensity at each of said frequencies to provide a measure of absorbance of said energy at said different frequencies; determining from said at least one amplitude modulated component of the electromagnetic energy information relating to the path length travelled by said component; and deducing, from the measure of absorbance and the information relating to the path length travelled, a measure of absorbance per unit path length travelled by the radiation for each of said frequencies. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. The method of determining a parameter related to the absolute or relative concentration of a chemical species within a medium that scatters and absorbs electromagnetic radiation by a medium comprising the steps of
generating electromagnetic radiation containing at least two components having differing frequencies; -
causing the temporal amplitude of at least one of said components to vary in a defined manner with time; introducing said electromagnetic radiation into said medium; detecting said electromagnetic radiation of said at least two components after it emerges from said medium; comparing the temporal amplitude variation of at least one of the detected components of said electromagnetic radiation with the temporal amplitude variation of at least one of the generated components of said electromagnetic radiation; determining from said comparison information relating to the path length travelled through the medium by at least one component of said radiation; measuring the intensity of at least two components of differing frequency of the detected electromagnetic radiation; comparing said measured intensities to the intensities of the introduced electromagnetic radiation to generate measures of the magnitudes of the absorbance of electromagnetic radiation by said medium at each of said at least two radiation frequencies; and deducing from said absorbance measures and said information relating to the path length travelled through the medium by said radiation measures of the absorbance of electromagnetic radiation by said medium per unit path length travelled by said radiation at each of said at least two radiation frequencies. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. An apparatus for determining a parameter related to the absolute or relative concentration of a chemical species within a medium that scatters and absorbs electromagnetic radiation comprising
means for generating electromagnetic radiation containing at least two components of differing frequency; -
means for causing the amplitude of at least one of said components to vary in a defined manner with time; means for introducing said electromagnetic radiation into said medium; means for detecting said electromagnetic radiation after it emerges from said medium; means for comparing the temporal amplitude variation of at least one of the detected components of said electromagnetic radiation with the temporal amplitude variation of said at least one of the generated components of said electromagnetic radiation; means for determining from said comparison information relating to the path length travelled through the medium by said at least one component of said radiation; means for measuring the intensity of at least two components of differing frequency of the detected electromagnetic radiation; means for comparing said measured intensities to the intensities of the introduced radiation to generate measures of the magnitudes of the absorbance of electromagnetic radiation by said medium at each of said at least two radiation frequencies; and means for deducing from said absorbance measures and said information relating to the path length travelled through the medium by said radiation measures of the absorbance of electromagnetic radiation by said medium per unit path length travelled by said radiation at each of said at least two radiation frequencies. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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39. The method of determining a parameter related to the absolute or relative concentration of chemical species within a medium that scatters and absorbs electromagnetic energy, comprising the steps of
irradiating the medium with elecromagnetic energy containing at least two components of different frequency, at least one of which is amplitude modulated; -
detecting electromagnetic energy emerging from said medium; measuring the intensity of the detected energy at each of said frequencies and comparing it to a measure of the irradiating intensity at each of said frequencies to provide a measure of absorbance of said energy at said different frequencies; determining from said at least one amplitude modulated component of the electromagnetic energy information relating to the path length travelled by said component; and processing the measure of absorbance and the information relating to the path length travel led to obtain a parameter related to the absolute or relative concentration of a chemical species. - View Dependent Claims (40, 41, 42, 43, 44)
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Specification