Speciation of As(III)/As(V) in water samples by a magnetic solid phase extraction based on Fe3O4/Mg–Al layered double hydroxide nano-hybrid followed by chemiluminescence detection

A novel magnetic solid phase extraction method was developed for the speciation of As(III)/As(V) in aqueous solutions utilizing Fe3O4-doped Mg–Al layered double hydroxide (LDH) as a nano-sorbent. The method is based on the separation and pre-concentration of As(V) by Fe3O4/Mg–Al LDH nano-hybrid prior to determination by a chemiluminescence (CL) technique. The CL route involves the oxidation of luminol by vanadomolybdoarsenate heteropoly acid in a basic media. Since the existing cations cannot be adsorbed by positively charged layers of the LDH and other potentially interferent anions had no considerable effect on the CL reaction, it provides a very selective and sensitive determination approach for As(V). The determination of total arsenic and hence indirectly As(III) involve the pre-oxidation of As(III) to As(V) by a mixture of hydrogen peroxide and potassium hydroxide. Several factors affecting the extraction and determination of the analyte were investigated and optimized. Under optimum conditions, the calibration graph was linear in the range of 5.0–5000 ng L−1. The limit of detection and enrichment factor was 2.0 ng L−1 and 80, respectively. The method was validated by the analysis of a standard reference material (NIST SRM 1643e), and successfully applied to the speciation of arsenic in several water samples with recoveries in the range of 93.3–106.7% for the spiked samples.