MEASUREMENT OF CARBON-13 CARBON-12 RATIOS BY FOURIER-TRANSFORM INFRARED SPECTROMETRY/

An approach to the measurement of C-13:C-12 ratios in isotopically enr iched samples Is described. The carbon in samples is converted into CO 2 gas by either combustion of organic material or acidification of car bonates. The gas is then measured by FTIR spectrometry. When spectra a re recorded at 0.25 cm(-1) resolution the magnitude of the isotopic sh ift is such that the areas of C-12 and C-13 rotational lines of the v( 3) vibrational band for CO2 can be measured and the isotopic compositi on determined by reference to a standard calibration graph, The relati ve standard deviation at natural abundance is 1.2%, which gives an abs olute limit of detection of 0.026 atom-% C-13. Details of the decompos ition procedures and a comparison of the results with those obtained b y mass spectrometry are also presented.