Influence of Surfactant and Ionic Liquid Media on Vapor Generation and Determination of Ag, Au, Cd, Cu, Ni, Sn, and Zn Using ICP-OES

Abstract

In this study, the main parameters affecting Ag, Au, Cd, Cu, Ni, Sn, and Zn vapor generation in a surfactant reaction media of cetyl trimethyl ammonium bromide (CTAB) were evaluated. Detection using inductively coupled plasma optical emission spectrometry has been optimized. Improvements in the analytical performance for Ag and Ni were also obtained when CTAB was combined with the ionic liquid l-butyl-3-methylimidazolium. Standards (1 mg L1) were prepared in acid media. The optimum concentrations of the reagents in the standards were: 2.5×10-5 M (CTAB) and 0.6 M (nitric acid), when only CTAB was used. When both modifiers were combined, the concentrations were: 2.5 ×10-3 M of 1-butyl-3-methylimidazolium bromide and 1.5 ×10-5 M CTAB. In this case, 0.3 M of nitric acid was added. The optimum concentration of sodium borohydride to generate the vapors was 2.2% (w/v) in 0.05% (w/v) NaOH. These vapors were swept from the forced outlet of a lab-made gas-liquid separator to the torch with an argon flow of O.7 mL min-1. The limits of detection ranged from 0.4 μg L-1 Cu to 6.9 μg L-1 Au. The detection limit for silver improved three-fold when CTAB was used together with l-butyl-3-methylimidazolium bromide (from 14.3 to 4.9 μg L-1). Relative standard deviations were below 5% (n=l 1) for all of the elements, except for Cd (11.3 μg L-1). Since best results were obtained for most elements using only CTAB, a study of interferences for this modifier was performed. It was observed that a surfactant agent, such as CTAB, was a better reagent to avoid interferences than a complexing agent, such as 8-hydroxyquinoline. Moreover, the method showed good accuracy when determining Cd, Cu, Ni, and Zn in a wastewater reference material.