METHOD FOR DETERMINING A SUBSTANCE CONCENTRATION AND DETECTOR DEVICE

Abstract

The invention relates to a method for determining a substance concentration in a sample comprising a liquid containing particles, in particular glucose in blood, wherein the refractive index of the liquid depends on the concentration of the dissolved substance and the particle density in the liquid is essentially constant. The method comprises acquiring a first PPG signal during a first period and estimating at least a portion of a noise spectrum from the first acquired signal, particularly in the frequency domain. At least a portion of the noise spectrum is used to derive the substance concentration or a change in the substance concentration.