Analyte concn. measuring method, e.g. for medical blood diagnosis

摘要

The method uses a spectrometer with at least two laser diodes IR sources. One diode emits radiation at a wavelength which the analyte strongly absorbs, while the other emits radiation at a wavelength which the analyte weakly absorbs or does not absorb. The injection currents of the laser diodes are amplitude modulated and have a phase shift of alpha = 180 deg. The radiation intensities directed towards a transmission cell have a corresp. time dependence and phase shift. Every change in concn. of the analyte changes the match between the modulation amplitudes of the diode currents. The DC current of the detector is then superimposed on the signal components containing the modulation frequency. The amplitude and phase of the signal components indicate the increase or decrease in analyte concn.