On-line, continuous determination of ~(13)CO_2 / ~(12)CO_2 ratios by non-dispersive infrared absorption in indirect calorimetry facilities

摘要

The objective of this study was to implement a cost effective, labour saving method for on-line measurement of ~(13)CO_2 concentrations based on Non Dispersive InfraRed absorption (NDIR). For this purpose, two NDIR gas-analysers were used for measuring total CO_2 and ~(13)CO_2 concentrations. The analysers were connected to an automated data-acquisition system where inflowing and outflowing air of the respiration chambers is analysed in rotation. Conversion of the signal from these analysers to ~(13)CO_2 concentrations and ~(13)C enrichment was done as follows: (1) Calibration of the units was performed with gas mixtures having a high and low known CO_2, ~(12)CO_2 and ~(13)CO_2 concentration. (2) To correct for overlapping absorption spectra of ~(13)CO_2 and ~(12)CO_2, six different gas mixtures containing 0% to 1.29% pure ~(12)CO_2 were used. Preliminary data of an experiment where a single dose of 300 mg of U-~(13)C-glucose was fed to two preraminant calves was analysed and compared with IsotopeRatio Mass Spectrometry (IRMS) data of parallel samples. These data showed a very good correlation of IRMS and NDIR ~(13)CO_2 enrichment. Based on experiments with 150 kg preruminant calves fed diets differing in natural ~(13)C enrichment the system showed that differences of one delta (8) can be detected. This allows for the quantification and measurement of the kinetics of labelled substrate oxidation in indirect calorimetry facilities.