A new selective method based on magnetic dispersive solid-phase extraction (MDSPE) and a zetasizer system is proposed for the determination of As(III)/As(V) species in some water and food samples. In the developed procedure, the crucial issue is that a novel adsorbent was synthesized and characterized by grafting L-glutathione (reduced) (GSH) onto a magnetic graphene oxide surface (GO/Fe3O4@GSH) and was also applied in quantitative adsorption of As(III)/As(V) ions. Moreover, GO/Fe3O4@GSH demonstrates selectivity towards As(III) in the presence of As(V). The best determination and speciation conditions were achieved by testing different nanocomposite quantities, the pH of the sample, type of desorption solution, sample and desorption solution volumes, and the effect of interfering ions. Due to features of the GO/Fe3O4@GSH nanocomposite such as a wrinkled structure and excellent dispersibility in water, GO/Fe3O4@GSH seems to be ideal for the fast and simple preconcentration/determination of As(III)/As(V) using methodology based on MDSPE and zetasizer measurement. As(III) was quantitatively recovered with the nanocomposite at concentrations between 0.5 and 1.5 mol L-1 of HNO3, while As(V) was not quantitatively recovered at any pH. The detection limit of the method was 0.1 mu g L-1 while the relative standard deviation was 1.0% for 0.5 mg L-1 As(III). The developed method was applied successfully for the determination of As(III) in some water and tea samples, and standard reference material samples with satisfactory results. Moreover, GO/Fe3O4@GSH can be applied for arsenic speciation due to its selectivity towards arsenite.