Abstract: Biological fluid samples containing proteins (e.g., blood plasma or saliva) are prepared for isotopic analysis by precipitating the proteins while leaving the isotopic ratio unaffected. This precipitation can involve adding metal ions, salts, organic solvents, or organic polymers. The sample is then centrifuged to allow transfer of the supernatant for isotopic analysis, e.g. by tunable diode laser absorption spectrometry to obtain a quantitative measure of the 2H and 18O isotope levels in the water relative to reference standards.

Abstract: An incoherent cavity ringdown spectroscopy (iCRDS) gas analyzer is provided with a gas flow path to introduce a sample gas into an enclosed volume bounded by a pair of mirrors defining an optical cavity. A pulsed broadband incoherent light source with a wavelength band that coincides with an absorption band of a specified gas species to be detected (e.g., NO2 or SO3) directs pulses of light into the optical cavity, while a photodetector is positioned to detect light exiting the cavity. A scrubber in an alternate flow path into the enclosed volume periodically scrubs the sample gas of the specified gas species. A processor determines the concentration of the specified gas species from the ringdown decay time of the photodetector measurement signals, with the periodic scrubbing of the sample gas providing a calibration reference from its slower decay time.

Abstract: Biological fluid samples containing proteins (e.g., blood plasma or saliva) are prepared for isotopic analysis by precipitating the proteins while leaving the isotopic ratio unaffected. This precipitation can involve adding metal ions, salts, organic solvents, or organic polymers. The sample is then centrifuged to allow transfer of the supernatant for isotopic analysis, e.g. by tunable diode laser absorption spectrometry to obtain a quantitative measure of the 2H and 18O isotope levels in the water relative to reference standards.