Potentiometric titration: a dynamic method to study the metal binding-mechanism of microbial biomass

Sorption of metals is not only dependent on solution conditions but also on the particle size of the biomass. Acidities of different size classes of mycelium of Rhizopus arrhizus were determined by potentiometric titration. It appears that the [50–200]μm size class has the largest capacity of fixation, 2 or 4 times greater than the other size classes. Despite these differences, the pKa of the different acidities, obtained using Henderson-Hasselbach's equation, are quite similar for all of them. Metal binding experiments are then performed, before the equilibrium, using an original method of potentiometric titrations with an ion selective electrode. This technique provides informations about the differences between the binding sites of the size classes during lead sorption. Moreover binding sites and mainly carboxylic groups are identified by Infrared Spectroscopy (FTIR).