Correction mechanism for Raman spectroscopy in emulsions.

Abstract

When the concentration of a fluid mixture is measured with Raman spectroscopy in emulsions instead of pure liquids, the signal strength is influenced by the light scattering of the droplets which gives wrong results. This work investigates this influence in the example of a water-toluene-acetone emulsion. For this purpose, the Raman spectroscopy is supported by a scattered light probe, which is intended to quantify the light losses when the dispersed toluene phase increases. The scattered light probe is aligned with the focal point of the Raman probe and detects the light from the 785 nm laser scattered by droplets. The aim is to determine the effects of emulsions on Raman spectroscopy dependent on the concentration of the disperse phase and to determine the acetone concentration of the mixture. The Raman signal decreases with increasing turbidity due to the disperse phase and the concentration of acetone can than no longer be determined from the signal. However, the increase in droplets increases the scattering of the excitation light, whereby a reduction in signal strength is detected. These measurements can be correlated to create a correction function. This makes it possible to correct the measured data of the acetone up to an RMSEP of 1.5 wt%.