Systematic Study for Determining As, Pb, Cd, and Se in Steel and Nickel Alloy Samples by GF AAS: Circumventing Matrix Interference with Extraction Based on Micellar Separation

This study proposes a matrix separation procedure based on micellar-mediated extraction (cloud point extraction - CPE) for determining As, Cd, Pb, and Se (potential contaminants) in nickel alloy and steel samples. Structural characterization and qualitative analysis of Ni alloy were conducted on the nickel alloy using scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS). After sample decomposition, ammonium o,o-diethyl dithiophosphate (DDTP) was used to complex the analytes and Triton X-114 as a non-ionic surfactant in CPE for matrix separation and extraction. Methanol acidified with 0.1 mol L-1 HNO3 was added to the surfactant-rich phase before the analytes determination by graphite furnace atomic absorption spectrometry (GF AAS). Parameters such as pH, complexing agent and surfactant concentrations, acid medium, complexation time, and type of diluent were evaluated. The obtained results indicated that the ratio DDTP:As was 3:1, DDTP:Cd and DDTP:Pb was 2:1, and DDTP:Se was 1:1. The enrichment factors were 6, 8, 14, and 13, and limits of detection were 1.5, 0.06, 0.31 and 0.27 µg g-1 for As, Cd, Pb, and Se, respectively. The method was applied for As, Cd, Pb, and Se determination in Inconel 625 nickel alloy and standard reference materials (AISI 4340 Steel - SRM® 361, AISI 94B17 Steel - SRM® 362, Chromium-Vanadium Steel - SRM® 363, and Nickel Alloy UNS - SRM® 864). Analyte recoveries lay above 88%, and relative standard deviations were lower than 5%. Application of cloud point extraction for matrix separation allowed the determination of low concentrations of As, Cd, Pb, and Se, constituting an environmentally friendly method.