PRECONCENTRATION AND SEPARATION OF ARSENIC SPECIES “IN THE FIELD” USING MODIFIED INORGANIC OXIDES AND THEIR SUBSEQUENT ICP-AES DETERMINATION IN THE LABORATORY

Abstract

For the concentration and separation of inorganic forms of arsenic, it is proposed to use aluminum oxide modified with polyhexamethylene guanidine (Al2O3-PHMG) and silica chemically modified with disulfide groups (DSS). The presence of protonated amines on the surface of modified aluminum oxide makes it possible to effectively concentrate anionic forms of arsenic from aqueous solutions. Arsenic(V) is quantitatively extracted by aminated aluminum oxide from solutions at a pH of 1.8–7.5 with a sorption equilibrium time not exceeding 5 min. The sorption capacity of Al2O3-PHMG with respect to As(V) is 55 μmol/g. To extract As(III), it is proposed to use a DSS sorbent that quantitatively extracts arsenic from solutions in the pH range 4.0–7.5. The sorption capacity of the DSS was 110 μmol As(III) per 1 g of sorbent. In the dynamic mode of concentration of inorganic forms of arsenic, the optimal conditions are pH 4.5. The flow rate of the solution is 1-1.5 ml/min. The volume of the passed solution is 300 ml at an analyte concentration of 1 mg/l. Quantitative desorption of As(V) from the surface of Al2O3-PHMG is achieved by 10 ml 0.05 M NaOH, adsorbed As(III) from the surface of DSS - 10 ml 2 M HCl. For separate concentration and determination of As(III) and As(V), a system of two sequentially connected concentrating cartridges was used: the first was filled with a DSS sorbent, the second with an Al2O3-PHMG sorbent. The proposed system was used to concentrate and separate inorganic forms of arsenic directly at the sampling site – natural underground and well drinking waters of Tyva Republic. The subsequent ICP-AES determination of arsenic was carried out after its desorption in laboratory conditions.