Depth profiling anlyses of oxidized coal was carried out by using step scan FT-IR/PAS spectrometer with a phase modulation technique. Variation of modulation frequency and phase angle gave considerably different spectra reflecting a depth profile of coal particle. Range of sensible depth was estimated by microscope observation of oxidized coal. Step scan FT-IR/PAS method was also applied to analyses of gasification chars. Depth profiling PAS spectra of gasification chars could be obtained using slow step scan and low modulation frequency.
