Use of Fluorescence Spectroscopy in Concentration and Supersaturation Measurements in Citric Acid Solutions

Abstract

Measurement of supersaturation is of critical importance in the operation and control of crystallizers. In this work, we report a novel spectroscopic technique to achieve the measurement of concentration and supersaturation in crystallizing solutions. In order to develop a sensor for this measurement, citric acid is chosen as the model solute, and the analytical technique involves fluorescence spectroscopy. Citric acid is a common food-grade compound with a wide range of applications that is exclusively produced by crystallization. The fluorescent properties of a probe, 8-hydroxy-1,3,6-pyrenetrisulfonate (pyranine), are used to provide concentration measurements in aqueous citric acid solutions, thereby providing for supersaturation estimation. The change in the relative emission peak intensities of the probe in different solute concentrations gives an excellent calibration curve for concentration measurements. It is also shown that, although pyranine responds to both its solvent microenvironment and the pH of the solution, it is still possible to measure concentration and supersaturation by using this fluorescence technique.

Keywords

Fluorescence Pyranine Supersaturation sensor Citric acid

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