FIELD: physics.;SUBSTANCE: spectrophotometre has a source (6) of radiation at several wavelengths in the direction of a specimen on a holder (4) and device (8) for detecting radiation after interaction with the specimen. The said specimen holder (4) enables to obtain several different path lengths for the flux radiated through the specimen. A computer device (10) receives an intensity-dependent input signal from the detection device (8), and is used to store intensity values of a defined flux of radiation which indicates the wavelength for two or more path lengths of several different path lengths, and for calculating a value which depends on the ratio of indexed intensity values for each of the two path lengths which can determine presence of the substance sought for in the analysed substance.;EFFECT: higher measurement accuracy.;7 cl, 2 dwg
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