Trace element analysis lanthanides

The ultimate goal for any trace element analysis of sea water is to determine the amount and chemical activities of the element associated with the diflFerent forms in which it may exist. The development of a procedure for such an analysis requires both a thorough knowledge of the physico-chemical behaviour of the element in question and methods capable of fractionating a sample. Presently, we have not the necessary knowledge of the chemistry of the lanthanides in sea water. In addition, the present state of the art of fractionation of sea water samples prohibits the development of such procedures as mentioned above. 

A. J.W. O Laughlin, Chemical spectrophotometric and polarographic methods 341 37B. S.R. Taylor, Trace element analysis of rare earth elements by spark source mass spectrometry 359 37C. R.J. Conzemius, Analysis of rare earth matrices by spark source mass spectrometry 377 37D. E.L. DeKalb and V.A. Fassel, Optical atomic emission and absorption methods 405 A.P. D Silva and V.A. Fassel, X-ray excited optical luminescence of the rare earths 441 W.V. Boynton, Neutron activation analysis 457 37G. S. Schuhmann and J.A. Philpotts, Mass-spectrometric stable-isotope dilution analysis for lanthanides in geochemical materials 471... 

The determination of trace and ultra trace amounts of individual Rare earth elements (REE) in complex matrices is one of the most challenging areas of analytical chemistry. Rapid studies made in analytical methodology have brought forth many powerful analytical tools for the determination of trace and ultra trace amounts of lanthanides. These are based on spectral, nuclear, X-ray, electrochemical and other chemical properties of lanthanides. Each technique provides a different and unique approach for the determination of lanthanides and offers certain advantages over others for a given analysis of complex materials. Hence it is desirable to compare the performance of various techniques available in terms of i) primary criteria like sensitivity, selectivity and precision and accuracy and ii) auxiliary criteria like speed, cost of equipment, availability etc. while choosing analytical technique. 

Applications of ICP-MS cover a wide range of sample types which often make use of its excellent sensitivity and isotope ratio capabilities, such as the determination of ultra-low levels of impurities in semiconductors, long-lived radionuclides in the environment, and geochronology. ICP-MS is well suited to the determination of the lanthanide series of elements in many geological applications. Sample preparation methods are similar to those generally used for trace metals analysis however, nitric acid is favored for sample digestion because other mineral acids contain elements which cause spectroscopic in-teferences. 

For many elements, the atomization efficiency (the ratio of the number of atoms to the total number of analyte species, atoms, ions and molecules in the flame) is 1, but for others it is less than 1, even for the nitrous oxide-acetylene flame (for example, it is very low for the lanthanides). Even when atoms have been formed they may be lost by compound formation and ionization. The latter is a particular problem for elements on the left of the Periodic Table (e.g. Na Na + e the ion has a noble gas configuration, is difficult to excite and so is lost analytically). Ionization increases exponentially with increase in temperature, such that it must be considered a problem for the alkali, alkaline earth, and rare earth elements and also some others (e g. Al, Ga, In, Sc, Ti, Tl) in the nitrous oxide-acetylene flame. Thus, we observe some self-suppression of ionization at higher concentrations. For trace analysis, an ionization suppressor or buffer consisting of a large excess of an easily ionizable element (e g. caesium or potassium) is added. The excess caesium ionizes in the flame, suppressing ionization (e g. of sodium) by a simple, mass action effect ... 

Cation-exchange chromatography in combination with a postcolumn derivatization is also suitable for analyzing uranium and thoriiun [46]. Because both elements are actinides and in close relation with lanthanides, they are always associated with them. Due to the lack of simple and sensitive colorimetric methods, the trace analysis of these elements represents a challenge. Although alternative analytical methods for these elements such as neutron activation analysis (NAA) [47] and ICP-MS [48] are described in literature, they are not suitable for routine analysis and are prone to interferences. Major interferences include... 

In the past, lanthanides were almost exclusively analyzed with element-specific methods such as AAS and ICP. However, spectral interferences are observed in trace analysis of lanthanides in geological samples, so that time-consuming extractions or group separations on ion exchangers have to be carried out first. In many cases, pre-concentrations are necessary, because the detection... 

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