Arsenic is widely present as various inorganic and organic species in nature,and exists mainly in the forms of As(Ⅲ) and As(Ⅴ) in environmental water.The environmental,biochemical and toxicological effects of arsenic depend on its existing form to a great extent.Therefore,the speciation analysis of arsenic in environmental samples is of great significance to environmental pollution monitoring and health risk assessment.Presently,inductively coupled plasma mass spectrometry(ICP-MS) has been widely used in the determination of trace arsenic.However,some difficulties would be encountered inevitably when ICP-MS is directly applied to the speciation analysis of arsenic in real samples.For example,different arsenic species cannot be distinguished,insufficient sensitivity and polyatomic ion interference of 40Ar35Cl on 75As during ICP-MS detection cannot meet the requirements for real sample analysis.Therefore,sample pre-treatment is often used prior to the ICP-MS detection,to enrich target analyte,separate multiple arsenic species and/or remove complex sample matrix.The purpose of this work is to synthesize new types of magnetic sorbents for the enrichment of arsenic species,and to establish a new ICP-MS with magnetic solid phase extraction(MSPE) for the quantification of inorganic arsenic species in environmental samples.Herein,sulfhydryl(—SH) modified epoxy-modified magnetic nanoparticles(Fe3O4@SiO2@GMA—S—SH MNPs) were prepared,and a method of MSPE/ICP-MS was developed for the analysis of inorganic arsenic species(As(Ⅲ) and As(Ⅴ)) in water samples.It was found that As(Ⅲ) was selectively adsorbed on Fe3O4@SiO2@GMA—S—SH MNPs in the pH value range of 5.0-9.0,while As(Ⅴ) was hardly adsorbed under this pH condition.For the determination of As(Ⅴ),As(Ⅴ) was reduced to As(Ⅲ) by Na2S2O3/KI prior to MSPE-ICP-MS detection,and the content of As(Ⅴ) was obtained by subtraction.The factors affecting MSPE were investigated in details.Under the optimal conditions,the limit of detection(LOD) of the developed method was 1.5 ng·L-1,the enrichment factor was 150 fold,the linear range was 5-3 000 ng·L-1,and the relative standard deviation(RSD)(c=10 ng·L-1,n=7) was 9.6%.To validate the accuracy,the developed method was applied to the analysis of arsenic speciation in a certified reference material of GSB07-3171-2014,and the determined results were in good agreement with the certified values.This method was also applied to the analysis of As(Ⅲ) and As(Ⅴ) in tap water and environmental water.The concentrations of As(Ⅲ) and As(Ⅴ) in tap water were 0.036 μg·L-1 and 0.043 μg·L-1,while those in lake water were 0.24 μg·L-1 and 0.43 μg·L-1,respectively.Spiked experiment was also conduced,and the recoveries were in the range of 80.9%-101%,and the RSD range of 1.5%-10%.The developed method has the merits of low detection limit,high enrichment factor,fast adsorption/desorption dynamics and good tolerance to interferences,and is suitable for the speciation analysis of inorganic arsenic species in real samples.