Methods and assemblies may be used for determining and using standardized spectral responses for calibration of spectroscopic analyzers. The methods and assemblies may be used to calibrate or recalibrate a spectroscopic analyzer when the spectroscopic analyzer changes from a first state to a second state, the second state being defined as a period of time after a change to the spectroscopic analyzer causing a need to calibrate or recalibrate the spectroscopic analyzer. The calibration or recalibration may result in the spectroscopic analyzer outputting a standardized spectrum, such that the spectroscopic analyzer outputs a corrected material spectrum for an analyzed material, and defining the standardized spectrum. The corrected material spectrum may include signals indicative of material properties of an analyzed material, the material properties of the material being substantially consistent with material properties of the material output by the spectroscopic analyzer in the first state.

The disclosure relates to a non-dispersive infrared (NDIR) gas sensor which detects the concentration of gas with a simple structure and method by manufacturing an optical waveguide with a gas-permeable polymer material instead of a conventional cavity or chamber type. An optical signal travels through the optical waveguide of gas-permeable polymer by total internal reflection, and the gas naturally penetrates the optical waveguide without the use of separate inlet and outlet openings, so that the optical signal and gas particles come into contact with each other within the optical waveguide. Since the optical signal detected by a photodetector at the other end of the optical waveguide after traveling while contacting the gas particles has properties changed according to the concentration of the gas which they have contacted in the optical waveguide, it is possible to measure the concentration of a specific gas from the detected optical signal.

The concentration of one or more gases in a surrounding fluid is measured using apparatus having a gas-permeable membrane separating an enclosed internal space within the apparatus from the surrounding fluid while allowing gases to diffuse from the surrounding fluid into the internal space. One or more sources sends infrared radiation along optical paths to one or more infrared detectors measuring intensity of radiation after absorption by gas(es) in the internal space and concentrations are determined from measured absorptions. The apparatus has more than one optical path through the internal space, enabling measurements of concentration over a greater range or enabling measurements of more than one gas present in very different concentrations or having very different infrared absorptivities.

Concentrations of individual hydrocarbons in a gas mixture are determined by measuring absorbance of mid-infrared radiation at specific wavelengths. Computation enables determination of concentrations of individual hydrocarbons despite overlaps of absorption bands.

This disclosure provides a method for imaging lymph nodes and lymphatic vessels without a contrast agent. The method includes providing, using an optical source, an infrared illumination to a region of a subject having at least one lymphatic component, detecting a reflected portion of the infrared illumination directly reflected from the region using a sensor positioned thereabout, and generating at least one image indicative of the at least one lymphatic component in the subject using the reflected portion of the infrared illumination.