USE OF FLUORESCENCE SPECTROSCOPY IN CONCENTRATION AND SUPERSATURATIONMEASUREMENTS IN CITRIC-ACID SOLUTIONS

Measurement of supersaturation is of critical importance in the operat ion and control of crystallizers. In this work, we report a novel spec troscopic technique to achieve the measurement of concentration and su persaturation 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 ac id is a common food-grade compound with a wide range of applications t hat is exclusively produced by crystallization. The fluorescent proper ties of a probe, 8-hydroxy-1,3,6-pyrenetrisulfonate (pyranine), are us ed to provide concentration measurements in aqueous citric acid soluti ons, thereby providing for supersaturation estimation. The change in t he 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 bo th its solvent microenvironment and the pH of the solution, it is stil l possible to measure concentration and supersaturation by using this fluorescence technique.