A method for using a multiplex sensor that provides enhanced selectivity and sensitivity. In this method, one or more parameters of a sample are measured by means of multiple spectroscopic techniques, and interferences from physiological and spectral variables are reduced or eliminated. One or more parameters of the sample are measured by means of at least two spectroscopic techniques, wherein the at least two different spectroscopic techniques are selected from the group consisting of: (a) infrared absorbance (b) scattering (c) emission (d) polarization, and (e) photoacoustics.