To identify and determine a chemical component of a complicate mixture by subtracting an intensity average value of spectral variables from a smoothed spectral variable, normalizing the output and the first spectral variable, obtaining a similarity degree of each spectral variable and comparing with a threshold value.

A sample is injected into a column, distributed in various speeds in the column and separated. A series of spectra is obtained by a spectrometer, so that every existing kind is detected. Spectral variables are smoothed, an intensity average value of the spectral variables is subtracted from the smoothed variable, and the output and the first spectral variable are normalized. Thereafter, a similarity degree of each spectral variable is measured, thereby selecting only spectral variables exceeding a threshold value. A total of the selected variables is plotted with respect to a time, whereby an intensified chromatogram is obtained. A quality index number which is in inverse relation to the amount of noises and a background intensity of data is calculated from the measured data. Accordingly, a mass chromatogram of the quality index number of a higher level is obtained.