A WAVELENGTH AND OPTICAL-PATH LENGTH SELECTION PROCEDURE FOR SPECTROSCOPIC MULTICOMPONENT ANALYSIS

Spectroscopic multicomponent analysis is the determination of the concentrations of the components in a mixture from the spectra of the mixture and of the pure components. This article presents a wavelength and optical path length selection procedure designed specifically for the quality control of pharmaceuticals. Wavelengths are selected for which the ratio of the absorbance to the standard deviation of the error of measurement is above some optimal value. This optimal value is chosen such as to maximize the 'quality' of the estimate of concentration. In a second step the information from flowcells of different optical path lengths is combined in an attempt to further improve the estimate of concentration. As the standard deviation of the error of measurement is a non-linear function of the absorbance, it is not possible to find a unique optimal set of wavelengths and optical path lengths for all possible mixtures of the pure components. This feature is not a limitation in applications where a priori information about the range of concentrations is available. In principle the method presented in this article could be applied to mixtures of an arbitrary number of pure components. For practical reasons mixtures of only two pure components were considered.