Direct determination of calcium in metals by atomic absorption spectrometry with a graphite furnace

Abstract

The direct determination of calcium in solid samples, such as tantalum, ferrotungsten, electrolytic iron and Spex G-4 powders, by atomic absorption spectrometry was studied with a graphite furnace. In comparison with the flame atomization method, the method is free from contamination from the reagents, rapid and easy to operate. Some experimental factors for the determination were tested: (1) the effect of argon carrier gas flow rate on the absorption of calcium, (2) the optimum atomizing temperature, (3) the calibration either by the peak height or by the peak area and (4) the matrix effect. When the peak height was measured, the absorbance signals from the calcium standard solution were not changed by the carier gas flow rate, while the absorption signals from solid samples decreased linearly in proportion to the increase of carrier gas flows. When the peak area used, the higher the carrier gas flow rate, the lower the absorbance of calcium both in the standard solution and the solid samples. The peak height values increased with increasing atomizing temperature, but the integrated values of the absorption spectrum approached a constant value above 2400°C. Calibration curves obtained from the integrated values were linear over 040 ng of calcium, while those obtained from the peak height values were not. Signal profiles for calcium differed according to the states of samples. A large difference came out in the absorbance peaks from ferrotungsten between a dissolved sample and a solid sample. The direct analysis of solid samples for calcium was successful for Spex G-4, tantalum and electrolytic iron, but not for ferrotungsten. The results of the analysis of solutions were generally in good agreement with those obtained for solid samples by peak area measurements. The detection limit for calcium was down to 5 ×10-11 g, and the relative standard deviation was 27%.