Systematic investigation of some metal cation interferences on the determination of molybdenum by flame atomic absorption spectrometry

The interference effects of some metal cations on the absorbance of Mo during its determination by flame AAS have been investigated, in air-acetylene flame, at a fuel flow rate of 1.8 L/min. While the interfering ion concentration was changing between 5 and 40 000 mg/L, the Mo concentration was taken as 10, 20 and 40 mg/L. It was shown that even at low concentrations of interfering ion there was a large suppression of Mo absorbance. No absorbance was observed for Mo in the presence of 50 time higher concentration of Mg, Ca, Sr, and Ba. These interference effects were suppressed by additions of 0.04% (m/v) sodium diethyldithiocarbamate (Na-DDTC), 2% (m/v) ammonium chloride, and 0.4% (m/v) sodium hydrogen phosphate. The interference from another group of elements, Mn, Fe, Al, Cd, Ni, Cr, Co, Cu and Zn, has been also investigated. In the presence of above mentioned metals, except Mn, the reproducibility of Mo absorption signal was not satisfactory. In the presence of Mn (5–40000 mg/L) the absorbance of Mo decreased significantly, however, the reproducibility was high. Molybdenum absorbance decreased under the influence of 5000–40000 mg/L of Fe, Co, Ni, 500–40000 mg/L of Cr. On the other hand, the absorption signal of Mo increased at about 20–40% in the presence of Zn and Cd. By the addition of 2% NH₄Cl the interference of these metals could be eliminated completely for all mass ratios of Mn: Mo and up to Mo: M mass ratio of 1: 10–1: 100 for the other metals, and reliable absorbance signals of Mo were obtained. The text was submitted by the authors in English.