A useful, high-sensitivity method for quantifying small amounts of coke on a catalyst was developed. A TGA/FTIR technique was used. Gases evolved from the sample during the thermogravimetric analysis were transferred from the furnace by a purge gas to the flow cell of an FTIR. The intensity of the infrared spectra of evolved gases, such as CO2, was measured as a function of time and displayed as a chromatogram. Integration of the chromatograms was compared to that of a standard sample and gave the amount of coke deposited on the catalyst. The carbon deposition on sulfated set-gel zirconia in the isomerization of n-butane at 200 degrees C was measured. The carbon content was 0.013 wt% following deactivation for 15 min and 0.06 wt% after 180 min.