Carbon isotopomers measurement using mid-IR tunable laser sources

Hollow waveguide integrated laser spectrometer for 13CO2/12CO2 analysis

Using hollow waveguide hybrid optical integration, a miniaturized mid-infrared laser absorption spectrometer for ¹³CO₂/¹²CO₂ isotopologue ratio analysis is presented. The laser analyzer described focuses on applications where samples contain a few percent of CO₂, such as breath analysis and characterization of geo-carbon fluxes, where miniaturization facilitates deployment. As part of the spectrometer design, hollow waveguide mode coupling and propagation is analyzed to inform the arrangement of the integrated optical system. The encapsulated optical system of the spectrometer occupies a volume of 158 × 60 × 30 mm³ and requires a low sample volume (56 µL) for analysis, while integrating a quantum cascade laser, coupling lens, hollow waveguide cell and optical detector into a single copper alloy substrate. The isotopic analyzer performance is characterized through robust error propagation analysis, from spectral inversion to calibration errors. The analyzer achieves a precision of 0.2‰ in 500 s integration. A stability time greater than 500 s was established to allow two-point calibration. The accuracy achieved is 1.5‰, including a contribution of 0.7‰ from calibrant gases that can be addressed with improved calibration mixtures.

Immediate biofeedback for energy balance via expired breath δ(13)CO2

Expired breath δ(13)CO2 measured in real time serves as a useful biomarker of altered macronutrient metabolism in response to changes in energy balance. Altered breath δ(13)CO2 is believed to be a result of changes in macronutrient oxidation and the kinetic isotope effect where enzymatic processes discriminate against metabolites naturally enriched with (13)C. Use of breath δ(13)CO2 as a rapid biofeedback of energy balance status will enhance an individual's ability to modify behavior during weight loss efforts. Herein we describe a novel approach for immediate biofeedback for energy deficit using a moderate exercise challenge. Our new mid-infrared isotope ratio-meter for δ(13)CO2 is a step toward miniaturization of a personal device for instant biofeedback for people attempting to lose weight.

Determination of 13C/12C Carbon Isotope Ratio

Isotopomers 12CO2 and 13CO2 absorbed into polystyrene films provide narrow, sharp, and well-resolved IR absorption bands for the nu3 antisymmetric stretching mode. This is exploited to set up an inexpensive FT-IR-based method for the measurement of the carbon isotope ratio. Accuracy of 2.5 per thousand delta13C units is readily achieved already at a low resolution of 2 cm(-1).