A COMBINATION OF SYNCHRONOUS FLUORESCENCE SPECTROSCOPY WITH CHEMOMETRIC TREATMENT AND INTERNAL STANDARDS IN NONAQUEOUS POTENTIOMETRIC TITRATIONS OF FULVIC-ACIDS

The acid properties of a soil fulvic acid (sfua) were characterized by potentiometric titration with tetrabutylammonium hydroxide in two non -aqueous solvents with high acid-base resolution power, N,N-dimethylfo rmamide (DMF) and acetonitrile. Synchronous fluorescence spectroscopy (SyF) was also used to monitor directly the sfua status during the pot entiometric titration in DMF. The potentiometric titration curves show ed no clear end-point and the analysis of the sets of spectra obtained at increasing neutralization degree, with a self-modeling curve resol ution method (SIMPLISMA), revealed the existence of two components wit h featureless concentration profiles. Internal standards (maleic, sali cylic and p-hydroxylbenzoic acids) were used to determine the amounts of acid groups with different acid strengths in the two non-aqueous so lvents. It was shown that the variations observed in the SyF spectra s ets of the internal standards are not correlated with those observed i n the sfua data. The splitting of the sfua groups in the non-aqueous t itration curves seems to be forced artificially depending on the stand ards used.