Molybdenum, determination Subject

Isaeva [181] described a phosphomolybdate method for the determination of phosphate in turbid seawater. Molybdenum titration methods are subject to extensive interferences and are not considered to be reliable when compared with more recently developed methods based on solvent extraction [182-187], such as solvent-extraction spectrophotometric determination of phosphate using molybdate and malachite green [188]. In this method the ion pair formed between malachite green and phosphomolybdate is extracted from the seawater sample with an organic solvent. This extraction achieves a useful 20-fold increase in the concentration of the phosphate in the extract. The detection limit is about 0.1 ig/l, standard deviation 0.05 ng-1 (4.3 xg/l in tap water), and relative standard deviation 1.1%. Most cations and anions found in non-saline waters do not interfere, but arsenic (V) causes large positive errors. 

Baucells et al. [53] applied ICPAES to the determination of very low levels of molybdenum (and cadmium) in soils. Among the most sensitive molybdenum lines, 202.030 nm proved to be an excellent analytical line although there were two iron lines close-by, at 201.99 and 202.074 nm, it was still found to be free from interference. The other molybdenum-sensitive lines were subject to interference from iron, chromium and vanadium. 

For determining alkyl groups it was proposed to subject a sample to destructive decomposition in a flow of hydrogen (the hydrogen acting simultaneously as a carrier gas) catalysed by a mixture of aluminosilicate oxide with quartz impregnated with tungsten and molybdenum oxides [222]. 

The fourth-derivative spectra of molybdenum complexes of tetramethyldithiocarbamate (tiram) fungicide were used for its quantification in commercial samples and in wheat grains [41], Atrazine and cyanazine were assayed in food samples by first- derivative spectrophotometry [42]. In order to improve results of assay, the first-derivative spectra of the binary mixture were subjected to chemometiic treatment (classical least squares, CLS principal component regression, PCR and p>artial least squares, PLS). A combination of first-derivative with PCR and PLS models were applied for determination of both herbicides in biological samples [42]. A first-derivative spectrophotometry was used as a reference method for simultaneous determination BriUant Blue, Simset Yellow and Tartrazine in food [43]. 

Some of the higher-alloyed austenitic stainless steels (S31600 and alloys with more chromium or molybdenum, or both, as well as the stabilized alloys) may form sigma or chi precipitates at temperatures between about 900 and 990°C. These precipitates are enriched with chromium and molybdenum and leave an envelope surrounding the grains depleted in these elements. ASTM A 262 describes testing methods to determine if an alloy has been subjected to precipitation of these phases. 

The determination of carbon in molybdenum and tungsten is already since 1969 the subject of studies in the frame of the working group "Sonder-und RefraktSrmetalle" of the Chemistry Committee of GDMB (Gesellschaft Deutscher MetalIhutten- und Bergleute). In the case of molybdenum (91) combustion methods carried out in 8 laboratories yielded the results... 

Allain, R, Berre, S., Premel-Cabic, A., Mauras.Y, Cledes, A., and Cournot,A. (1991). Urinary elimination of molybdenum by healthy subjects as determined by inductively coupled plasma mass spectrometry. Magnesium Trace Elem. 10(1), 47-50. 

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