Background: In recent years, there has been growing interest in the analysis of arsenic, due to its high toxicity and abundance in the environment [1]. Arsenic occurs in natural waters mainly in inorganic trivalent and pentavalent oxidation states. Although there are a number of analytical methods to detect arsenic, none of them are suited to on-site analysis[2]. Spectrophotometric methods based on the formation of molybdoarsenate with subsequent reduction to heteropoly blue are also frequently studied for the determination of arsenic [3], [4]. Methods: In this study, a simple and sensitive method has been developed for spectrophotometric determination of arsenic after magnetic solid phase extraction (MSPE). The method is based on the ion- pair formation of molybdoarsenate with methyl violate, followed by extraction of formed ion- pair onto the modified magnetic nanoparticles and subsequent elution of it for final spectrophotometric determination. Magnetic nanoparticles coated with oleic acid were used as adsorbent in MSPE procedure. Experimental parameters for both spectrophotometric reaction and extraction procedure have been optimized. Results: Under optimized conditions, the calibration curve for arsenic determination showed a good linearity in the range 10-400 μg l-1. The relative standard deviation (%RSD) for 50 μg l-1 of arsenic was 2.6% and detection limit (S/N= 3) was estimated to be 2 μg l-1. Conclusion: The developed method was successfully applied for determination of arsenic in water samples. The results demonstrated that the developed method is simple, inexpensive, accurate and remarkably free from interference effects.
