The determination of rare earth elements by flame emission spectroscopy.

Rare earth elements are added to high quality steels to improve certain physical properties. This has led to increased interest in rare earth chemistry and particularly in the development of methods to determine trace levels of these elements in steel. Flame emission spectroscopy can provide a useful method for rare earth element analysis being concerned with lower energy levels than the conventional arc or spark emission system and preferred to the classical methods which have been criticised on grounds of sensitivity, selectivity or speed of analysis. The light lanthanoid elements Ce (primarily), La, Nd and Pr, were investigated using a reducing nitrous oxide/acetylene flame in a conventional atomic absorption spectrometer switched to an emission mode. Useful analytical lines and bands were determined and recorded for each element. The importance of flame temperature and flame chemistry for the efficient production of free atoms of these highly refractory rare earth elements was confirmed. The usefulness of an ionisation suppressor, e.g. K or Cs, and organic media to enhance the emission signal was also confirmed. The 2o detection limits were obtained for the four elements. The interference effects of typical elements found in specialised steels and the extent of mutual rare earth interference were investigated in detail and spectral interference found to be severe for some elements. The requirement for separation of the lanthanoids due to spectral interference and the desirability of lowering the available detection limit led to the investigation of a number of methods, e.g. ion exchange; solvent extraction and precipitation, to remove and concentrate the rare earth elements from the steel matrix. Two useful analytical methods have been developed involving solvent extraction, precipitation and flame emission spectroscopy for the determination of single rare earth additions to steel (involving hydroxide precipitation) and cerium in the presence of rare earth mixtures in steel (involving oxalate precipitation).