Abstract: Experimental conditions for carrying out difference spectroscopy in a two component mixture have been studied. Factors influencing results of the measurements are also discussed, such as: (1) the selection of the common band and the optimum adoption of its cursor indication, (2) the operating parameters, i. e., slit width, scan speed, and time constant, in particular, the wavenumber accuracy. Improved results so far obtained are examplified by measurement of the spectra of individual components of geometrical isomers of schisantherin as well as epimers of Qinghaosu derivatives.