Infrared absorption spectroscopy of liquids employing a thermal detector
AssigneeDiax Corporation
InventorLloyd B. Kreuzer
Life of this patent
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Abstract
In an infrared laser absorption spectrometer, an infrared laser beam of predetermined wavelength, in the infrared absorption spectrum, is beamed into a liquid sample under analysis. Components of the liquid sample absorb energy from the infrared beam, as a function of the infrared wavelength of the beam, to produce heating of the liquid. A thermal detector is disposed in heat exchanging relation with the liquid sample for detecting the heating effect in the liquid due to absorption of the infrared radiation. This detection scheme is particularly useful for monitoring the effluent of a liquid chromatograph as it provides specific detection.
Claims14
In a laser infrared absorption apparatus:
- cell means for interposing a liquid sample medium to be analyzed in a beam of infrared radiation;
- laser means for producing the beam of infrared radiation as a beam of coherent infrared radiation;
- means for modulating the intensity of the beam of coherent infrared radiation;
- and
- thermal detection means disposed in heat exchanging relation with the liquid sample and being responsive to the temperature of the liquid sample for detecting the heating effect at the modulation frequency or harmonics thereof in the liquid sample due to the absorption of infrared radiation by the sample from the modulated beam of infrared radiation.
The apparatus of claim 5 wherein the distance from the thermal detector means to the outer diameter of the infrared beam path in said detector cell is less than V.sup.3 /.omega..sup.2 .alpha. where V is the velocity of the liquid stream in the detector cell, .omega. is the infrared beam modulation frequency in radians, and .alpha.=K/PC where K is the thermal conductivity, P is the density and C is the specific heat, respectively, of the liquid sample.
In a method for detecting absorption of infrared radiation by a liquid sample from a laser beam the steps of:
- producing a beam of infrared radiation as a beam of coherent infrared radiation;
- modulating the intensity of the beam of coherent infrared radiation at a modulation frequency f.sub.0 ;
- irradiating a liquid sample medium to be analyzed with the modulation frequency or harmonics thereof due to the absorption of infrared radiation by the sample from the modulated beam of infrared radiation.
Dependencies are inferred from the claim text.