Binary solvent were prepared by mass using a Sartorius CP225D
analytical balance with an accuracy of ±0.01 mg. The uncertainty in
the mole fraction of mixed solvents was estimated to be within
±0.0003. 25 g of binary solvents were introduced into a double
jacketed reactor thermostatted at (T ± 0.1) K (Polystat Huber
CC2). An excess of the solid gallic acid was added to the liquid
phase and the solution was continuously stirred with a magnetic
stirrer. To check the equilibrium, a sample of the liquid phase
was taken through a 0.2 lm pore syringe filter and the concentration
was measured by UV/visible spectrophotometry (Beckman
Coulter UV/vis spectrophotometer model DU-520) at 300 nm. The
wavelength of 300 nm was determined to be the most adequate
for gallic acid quantification because of the maximum absorbance
at this wavelength. When the concentration of gallic acid in the liquid
phase remained constant, it was assumed that the system was
at equilibrium. Several equilibrium times have been tested (from 1 to 6 h), and it appears that 3 h is always sufficient to reach equilibrium.
Tow independent experiments were realised to determine
the gallic acid solubility. The reproducibility of the data was within
0.5%.