External Raman standard for absolute intensity and concentration measurements

Abstract

A new method of calibrating Raman intensities is described, which uses a sapphire window as an external intensity standard. This method overcomes problems often encountered using conventional internal standards techniques, resulting either from refractive index differences or chemical interactions of the standard with the sample. The new method is demonstrated by measuring solution concentrations and Raman cross sections in various liquids. Concentration measurements are performed using the second derivative variance minimization (SDVM) algorithm to simultaneously subtract the sapphire window spectrum, normalize the solution spectral intensity and quantify solute concentration. The absolute Raman cross sections of several pure liquids were determined by comparing intensities of the sapphire-normalized Raman bands to that of benzene and other liquids whose Raman cross sections are known.