A new approach for the determination of the iso-electric point of nanoparticles

A new and simple experimental approach is proposed for the determination of iso-electric point (IEP) of nanoparticles suspension using ultraviolet–visible absorption spectroscopy. The suspension was first ultrasonicated to obtain appropriate particle dispersion and the optimal ultrasonication time was investigated by measuring the UV–vis spectra. The absorbance of the suspensions was then determined as a function of pH values. The absorbance at λ = 245 nm changed from positive to negative after the weakest absorbance was reached. The point of intersection of y = 0 and the curve indicates the IEP of the nanoparticle dispersion. The value so obtained was close to those determined by the conventional electrokinetic method and from prediction.