Lanthanide determination interferences

Spontaneous emission and radiative lifetime of lanthanide excited state in condensed phases is determined by the electromagnetic field and the index of refraction as shown in eq. (3). In nanocrystals, spontaneous emission of photons is influenced by two mechanisms (1) the non-solid medium surrounding the nanoparticles that changes the effective index of refraction thus influences the radiative lifetime (Meltzer et al., 1999 Schniepp and Sandoghdar, 2002), (2) size-dependent spontaneous emission rate due to interferences (Schniepp and Sandoghdar, 2002). 

Trace and ultratrace impurities (Ti, Zn, Ga, Nb, Sn, Sb, Te, several lanthanides, Ta, Ir, Pt, Pb, Bi and U) in the xgg range and below in wet digested steel samples (with aqua regia in a microwave oven) have been determined by ICP-ToFMS. For Ca determination in steel, an analytical procedure was introduced with microwave assisted digestion and matrix separation by flow injection ICP-MS to solve the interference problem ( C 02 and Si °0 on analyte ion " " Ca+) after treatment with H2SO4 and HF, and a detection limit of 0.6(xgg was obtained. The determination of trace and ultratrace impurities in high purity (4N) copper samples, after digestion... 

As an example, in the determination of alkaline earth metals in the presence of lanthanides by the methods involving CyDTA complexes described in Section 21-5, the rates of reaction of lanthanides are too slow to cause interference, and simple methods of measurement should be possible. The differences between the rates of reaction of the various alkaline earth metals are so small, however, that a simple procedure cannot be applied. 

At pH 2.6, Th, Zr, Ti, Fe(III), Bi, In, Al, and Y (but not the lanthanides) interfere. Reducing the pH minimizes these interferences and even masks yttrium completely. Iron(III) and cerium(IV) are masked by reduction with ascorbic acid. Oxalate, sulphate, fluoride, and phosphate interfere in the determination of scandium. 

If the sample contains plenty of inorganic cations, the trace components of the solutions can be separated by precipitation of the main components with a suitable reagent or by increasing the pH of the solution. However, some suitable metal cation must usually be added into the solution to obtain sufficient precipitation. Commonly used cations are Fe Al, trivalent lanthanide, Mn , and Mg ions. Compounds to be precipitated are often hydroxides, halides, sulfides, or sulfates. The cation used must not cause any interference in the determination, and it must be added in sufficient quantity to ensure adequate precipitation. 

Furthermore, lanthanides form stable complexes with polydentate chelators like DTPA, which exhibit a noncyclic structure. Two structures are depicted in Scheme 2. The following examples are only representatives for the variety of analyte molecules that can be determined by these kind of lanthanide complexes. Structure 9 employs a quinolyl ligand both as chromophore and acceptor for Zn ". The emission of the europium ion is strongly enhanced upon binding of Zn " and showing distinct selectivity over other biologically relevant metal cations in aqueous solution at neutral pH [29]. The luminescence of the chelate 10 is efficiently quenched by Cu " ions in aqueous medium [30]. The presence of Fe ", Co ", Ni ", Cr ", and Mn " interferes with the determination of Cu, although to a relatively small extent, whereas the ions Zn ", Cd ", Hg, and Pb do not interact with probe 10. 

An S preceding an atomic weight indicates the isotope enriched in our spike. The underlined atomic weights are measured mass spectrometrically and are chosen to be relatively free of isobaric interferences from other elements, wherever possible. The masses enclosed in parentheses are measured during the determination of an adjacent lanthanide in order to correct it for isobaric interferences. Barium and Hafnium are listed to permit calculation of their interferences with the isotopes of contiguous lanthanides. 

Geochemical studies often require determination of all the lanthanides (and often yttrium as well) in various geological matrices such as rocks, sediments, coal, etc. In most geological matrices, the light rare earths (e.g.. La and Ce) are much more abundant than the heavier rare earths (e.g., Tb and Tm). Therefore, the analytical technique for this application should have multi-element capabilities, large dynamic range, and limited susceptibility to interferences. This problem was not easily fulfilled before the advent of ICP-AES, which provided the first analytical technique with the potential to cover the whole suite of rare earths in a reasonable time. 

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