Determination of chromium traces by atomic ionization spectroscopy in aqueous standard solutions and in gallium arsenide using the «rod – flame» atomization system

The results of the determination of trace amounts of chromium in aqueous standard solutions of chromium and in high purity gallium arsenide using atomic ionization spectroscopy are presented. Single — and two-step schemes of chromium atom excitation from the ground state 3d 5 4s 7 S 3 to septet states 3d 5 4p 7 P 2,3,4 , 3d 4 4s4p 7 P 2,3,4 were studied using a «rod – flame» atomizer. A mechanism of forming atomic-ionization signal for two-step excitation schemes is revealed. The most effective two step excitation schemes for chromium atoms were determined and experimentally studied at different wavelengths λ 1 = 425.4 nm, λ 2 = 451.4 nm; λ 1 = 425.4 nm, λ 2 = 426.1 nm. The low limit of chromium detection in aqueous water solutions was 50 pg/ml. The analytical potentiality of the «rod – flame» system for determining traces of chromium in gallium arsenide solutions has been demonstrated. The possibility of determining traces of chromium in gallium arsenide using a flame – rod atomizer at a level of 5 × 10 –7 % is demonstrated. Two methods are proposed to increase the selectivity and sensitivity of atomic-ionization determination of chromium: optimization of the temperature program of the flame – rod atomizer and the use of two-stage excitation of chromium atoms. It is shown that the main interfering factor is the background attributed to the matrix ionization. Methods are proposed to reduce or eliminate the matrix impact, which ensure direct determination of elements in samples.