2. Experimental
We used a set of AAS VARIAN AA 240 DUO, which includes flaming VARIAN 240F and electrothermal
VARIAN 240AZ spectrometers. For electrothermal atomizer we used graphite cuvette VARIAN, ultra high purity
nitrogen was used as the carrier gas. Voltammetric measurements were carried out with the analyzer TA-4
(“Tom’analit”, Tomsk) with polyethylene impregnated graphite electrode. As a reference electrode, silver/silver
chloride electrode was used. Calibration solutions of gold, lead, nickel, and cobalt were obtained by diluting the
standard samples obtained from Sigma. Nitric, hydrofluoric and hydrochloric acids were purchased ultrapure quality
and sub boiled by Milestone SubPur systems, di-n-octyl sulfide CAS № 2690-08-6 obtained from Sigma.