Attenuated total reflection Fourier transfer infrared(ATR/FT-IR) spectroscopy evaluated oily substances with ester bonds and fatty acids in an n-hexane solution. Experiments analyzed the residue on an internal reflection element after n-hexane evaporation. When the amount of residue was 0.5-5 micrograms, absorbance data identified triolein and oleic acid. Researchers compared ATR/FT-IR analysis with gravimetric analysis for determining the composition of oily substances extracted from an undershirt used for six months. ATR/FT-IR analysis was approximately equal to gravimetric analysis when identifying oily substances with ester bonds using the calibration curve for a mixture of 65 percent triolein and 35 percent palmitic acid n-hexadecyl ester. 13 refs.