A chromatograph detector contains an arrangement for detecting a series of absorption spectra from a specimen flowing out of the column of the chromatograph at a number of times a short intervals. Each absorption spectrum is composed of a set of absorption data wrt. the wavelength and the light passing through the specimen. A chromatogram is produced from the series of absorption spectra. Peak sections contg. a target component of the specimen in the chromatograph are detected by another arrangement. A similarity value is computed for the absorption spectrum at any time and a standard spectrum for the target component. A threshold value is derived from the spectrum at the selected time, the standard spectrum and a chromatograph noise level . A further arrangement decides whether the spectrum is similar to the standard spectrum by comparing the similarity value with the threshold.
