Jerome,
Two references:
Haisch et al 1994. A sensitive isotope selective nondispersive infrared
spectrometer for 13CO2 and 12CO2 concentration measurements in breath samples.
Isotopenpraxis Environ. Health Stud. 30 247-251.

Irving et al 1986. Measurement of 13CO2/12CO2 abundance by nondispersive
infrared heterodyne ratiometry as an alternative to isotope ratio mass
spectrometery.
Anal. Chem. 58 2172 2178


At 05:47 PM 3/30/99 +0200, you wrote:
>Dear isogeochemists,
>
>Do some of you have knowledge or references concerning the measurement of
>13CO2/12CO2 ratios (either at 13C-enriched or natural abundances)
>by infrared absorbance techniques (FTIR, laser diodes, NDIR ?)
>What are the performances of such methods ?
>
>Thanks in advance from France.
>
>
>
>------------------------------------------------------
>Jerome Balesdent, Directeur de Recherches INRA
>
>Laboratoire d'Ecologie Microbienne de la Rhizosphere
>(UMR CNRS/CEA #163)
>DEVM - CEA - Centre de Cadarache
>F13108 Saint-Paul-lez-Durance Cedex
>
>tel : +33 4 42 25 77 54   secr: +33 4 42 25 27 53
>fax : +33 4 42 25 66 48   [log in to unmask]
>------------------------------------------------------
>
>
David Harris
Stable Isotope Facility
Department of Agronomy and Range Science
122 Hunt Hall
UC Davis, Davis CA 95616
Voice (530) 754 7517, Fax 752 4361
http://stableisotopefacility.ucdavis.edu