Extraction of arsenic(III) in aqueous two-phase systems : a new methodology for determination and speciation analysis of inorganic arsenic.

Abstract

This work utilizes the liquid–liquid extraction technique of aqueous two-phase systems (ATPS) formed by a polymer and electrolyte to develop a novel methodology for the extraction, determination, and speciation analysis of inorganic arsenic. To optimize the methodology, the following parameters were studied: pH of the system, nature of the ATPS-forming electrolyte and the polymer, tie-line length (TLL) of the system, type and concentration of extractants, and the mass ratio of the top and bottom phases. The highest extraction (%E = 98%) was obtained for an ATPS composed of L64 + Na2SO4 + H2O, at pH = 6.00, TLL = 33.55% w/w using the ammonium pyrrolidine dithiocarbamate (APDC) extractant in a molar ratio (APDC/As(III)) of 960, and with a mass ratio of 1/4. In these same conditions, As(V) was not extracted satisfactorily (%E = 18%) to ATPS top phase, with a separation factor equal to 530 after three extractions, showing the great potential of the system for the speciation analysis of inorganic arsenic. Moreover, the method was validated employing HG-ICP OES with a coefficient of determination of 0.9957 and limits of detection and quantification equal to 0.20 μg kg−1 and 0.66 μg kg−1, respectively, proving that the method is capable of detecting the low concentrations required by legislation. The relative standard deviation (RSD) values varied between 4.88 and 9.45%, and the RSD in inter-day precision was 11.07%, which are in accordance with the limits of the validation guide used by the National Institute of Metrology, Quality and Technology, COD-CGCRE-008. Furthermore, relative error rates ranged from −7.44 to 9.90% and recovery percentages were between 92.6 and 110% for the accuracy studies. This method was also applied in a spiked tap water sample, presenting a recovery value equal to 87.10%.