Thermal solid sampling, atomic spectroscopy

The separation of yttrium from the lanthanides is performed by selective oxidation, reduction, fractionated crystallization, or precipitation, ion-exchange and liquid-liquid extraction. Methods for determination include arc spectrography, flame photometry and atomic absorption spectrometry with the nitrous oxide acetylene flame. The latter method improved the detection limits of yttrium in the air, rocks and other components of the natural environment (Deuber and Heim 1991 Welz and Sperling 1999).Other analytical methods useful for sensitive monitoring of trace amounts of yttrium are X-ray emission spectroscopy, mass spectrometry and neutron activation analysis (NAA) the latter method utilizes the large thermal neutron cross-section of yttrium. For high-sensitivity analysis of yttrium, inductively coupled plasma atomic emission spectroscopy (ICP-AES) is especially recommended for solid samples, and inductively coupled plasma mass spectroscopy (ICP-MS) for liquid samples (Reiman and Caritat 1998). 

We will now discuss resonance techniques that are useful for studying liquid and solid samples. In these methods the differences in population between magnetically separated sublevels, due to the thermal Boltzmann distribution, are utilized. Magnetic field splittings are always small in comparison to kT, which is about 1/40 eV at room temperature. Thus population differences will always be small, and the number of atoms required is much larger than for the optical resonance techniques. However, very sensitive resonance detection techniques based on RF signals have been developed. The field of resonance spectroscopy of non-gaseous media is covered in [7.37,38]. 

In the application of atomic emission spectroscopy for quantitative analysis, samples must be prepared in liquid form of a suitable solvent unless it is already presented in that form. The exceptions are solids where samples can be analysed as received using rapid heating electro-thermal excitation sources, such as graphite furnace heating or laser ablation methods. Aqueous samples, e.g. domestic water, boiler water, natural spring, wines, beers and urines, can be analysed for toxic and non-toxic metals as received with... 

Pure samples of the A and B phases were finally obtained. They consisted in finely divided and bluish grey powders for the A phase and brownish grey for the B ones. The sodium content was determined by chemical analysis (flame spectroscopy) after dissolution in diluted HF. Another method consisted in an ultimate thermal decomposition into silicon above 500 °C and measurement of the weight loss due to sodium evaporation. The obtained Na/Si atomic ratio for the A phase was in any case close to 0.158 and, consequently, it was attributed the formula NaSie- In three samples of the B phase obtained at 340, 380 and 445 °C, much lower Na/Si atomic ratios were obtained 0.076, 0.064 and 0.020, respectively. These results indicated that the B phase was a kind of solid solution of a few sodium atoms in a silicon matrix. The Na Si (0.02 < x 0.076) general formula was thus adopted. 

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