Aqueous ammonia as matrix effect suppressor in determination of noble metals by electrothermal atomic absorption spectrometry: A novel approach

A simple, fast and precise method for the electrothermal atomic absorption spectrometry (ETAAS) determination of Au(III), Ag(I), Pd(II) and Pt(IV) from a single aliquot at the level of 10−4% in complex samples was developed. The method is based on reducing the interfering effect of Al, Fe, Cu and Ni macrocomponents on determination of Au(III), Ag(I), Pd(II) and Pt(IV) by ETAAS by adjusting the acidic sample solution to pH 9-11 using aqueous ammonia. As a result, 98.4% of Al and 99.7% of Fe precipitated smoothly at room temperature and without additional reagents needed. Furthermore, Au(III), Ag(I), Pd(II) and Pt(IV) did not co-precipitate and remained in the soluble form as ammonia complexes. While soluble ammonia Ni and Cu complexes were also produced, they decomposed in a graphite furnace at 400 °C and did not interfere with ETAAS determination of noble metals. In addition, the benefit of the ETAAS determination of Au(III), Ag(I) in the ammonia complexes is that there were no losses of Ag and Au due to the formation of insoluble AgCl and vaporization of gold and silver chlorides before atomization or incomplete dissociation in the gas phase when conventional sample treatment methods were used The relative standard deviations (R.S.D.) were in the range of 8-10% for determination of Au and Pd in aluminium catalysts, Ag in pure gold samples, and Pt in nickel tailings.