Pressure broadening of an infrared absorption band of gaseous CO2 makes measurement of a band intensity very much easier and also much more precise in comparison with the results obtained by measuring the intensity of a single line in a gas-phase spectrum. The isotopic shift of the v3 bands for carbon dioxide centered at 2350 cm−1 is sufficient to completely separate the P branch for 13CO2 from the two branches for 12CO2. The intensity ratios can be measured accurately on a low-resolution FT-IR spectrometer when the CO2 is pressurized to 10 bar (106N m−2) with N2, permitting isotope ratio differences as small as 0.02 atom % above the natural abundance of 1.11 atom % to be detected.
McGawB. A.MilneE. and DuncanG. J, Biomed. Environ. Mass Spectrom.15, 467 (1988).
2.
JohansenH. S. and MiddelboeV, Appl. Spectrosc.34, 555 (1980).
3.
IrvingC. S.KleinP. D.NavratilP. R. and BouttonT. W, Anal. Chem.58, 2172 (1986).
4.
LeeP. S. and MajkowskiR. F, Appl. Phys. Lett.48, 619 (1986).
5.
WongW. W., Int. J. Appl. Radiat. Isot.36, 997 (1985).
6.
OkanoK.KitoO.KokubunN. and TotsukaT, Soil Sci. Plant Nutr.29, 369 (1983).
7.
MilatzJ. M. W.KluyverJ. C. and HardebolJ, J. Chem. Phys.19, 887 (1951).
8.
KluyverJ. C. and BlokhuisE. W. M, Physica20, 427 (1954).
9.
TysonL. L.VickersT. J. and MannC. K, Appl. Spectrosc.38, 697 (1984).
10.
McDowellR. S., Anal. Chem.42, 1192 (1970).
11.
KindnessA. and MarrI. L, Analyst121, 205 (1996).
12.
WilsonE. B. and WellsA. J, J. Chem. Phys.14, 578 (1946).
13.
BurchD. E.GryvnakD. A.PattyR. R. and BartkyC. E, J. Opt. Soc. Amer.59, 267 (1969).
14.
KnappG.RaptiS. E.KaiserG.TolgG.SchramelP. and SchreiberB, Fresenius Z. Anal. Chem.308, 97 (1981).
15.
McGawB. A., personal communication.
16.
WinklerF. J., in Chromatography and Mass Spectrometry in Nutrition Science and Food Safety, FrigerioA. and MilonH, Eds. (Elsevier, Amsterdam, 1983), p. 173.
17.
V. G. Isogas Ltd., Middlewich, England, Specifications for SIRA 12.
