Measurement of 13CO2/12CO2 abundance by nondispersive infrared heterodyne ratiometry as an alternative to gas isotope ratio mass spectrometry.
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abstract
We report the performance of a prototype nondispersive Infrared heterodyne ratiometer in the analysis of seven reference gas samples containing 3.0% CO2in air, and isotopic enrichments from -85 to +329 8% vs. PDB as measured by gas isotope ratio mass spectrometry. The instrument response in volts1(V1) varied from -0.51 to 1.22 over the range of -85 to +329%o. A mean instrument response with a 0.0015 standard deviation (0.375%o) required 110 s of signal averaging at a 1-s sampling rate. The calibration curve of instrument response vs. 8%o was linear over the entire range and had a slope of 0.003 89 0.000 03 (SD), an intercept of -0.188 0.005, and a standard error of 0.009. With this curve, 45 s of data acquisition at a mean instrument response of -0.280 V1attained a standard deviation of 1.3%o at -28.7%o. Nondispersive infrared heterodyne ratiometry can analyze the 13C content of respiratory gas samples with acceptable accuracy and sensitivity for clinical studies. 1986, American Chemical Society. All rights reserved.