Platinum group metals as chemical modifiers for the determination of molybdenum by electrothermal atomic absorption spectrometry

Abstract

Platinum group metals (Pt, Rh, Ru, Ir) were tested as chemical modifiers for the determination of Mo and compared with modifiers that have been proposed previously (Mg and BaF₂). The mass of the chemical modifiers was carefully optimized. It was found that platinum group metals (0.2 µg of Ir or 0.5 µg of Ru or 1 µg of Rh or 1.5 µg of Pt) increased the maximum permissible pyrolysis temperature (T_pyr) from 1500 °C without modifiers to 1800 °C. The characteristic mass without modifiers was 7.0 pg, whereas in the presence of 0.2 µg of Ir or 3 µg of BaF₂, it was 3.1 and 6.4 pg, respectively, measuring the peak height absorbance with a moderately used graphite tube (around 70 atomization cycles). The characteristic mass derived from integrated absorbance measurements was in all cases 5.1 ± 0.1 pg. The limits of detection were 0.10, 0.10 and 0.28 µg l^–1 in the absence of chemical modifiers and in the presence of 0.2 µg of Ir and 3 µg of BaF₂, respectively, measuring the peak height absorbance with a moderately used graphite tube. From integrated absorbance measurements the corresponding limits of detection were 0.27, 0.31 and 0.42 µg l^–1. The efficiency of these modifiers was tested in the determination of Mo in animal feeds. Certified reference materials (Rye Grass, CRM 281, and White Clover, CRM 402) and recovery tests were used to check the accuracy of the proposed method. Accurate results and good agreement with the certified values were found in the presence of platinum group metals.

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