Molybdenum, determination spectrophotometry

The graphite furnace technique for atomic absorption spectrophotometry permits molybdenum determination at the ng level with small sample volumes. This technique is, however, prone to matrix interferences when used for molybdenum analysis. The boiling point of molybdenum is about 4600°C, about 1800°C above the maximum temperature obtained in the graphite furnace. Therefore, molybdenum atomization can only take place by a mechanism which includes the formation of a compound that is volatile at 2800°C. Molybdenum atoms will only be produced if the volatile molybdenum compound dissociates at this temperature. Any ions or compounds which affect the complicated atomization mechanism will alter the sensitivity of the method. This crucial fact is the primary reason for the extreme matrix sensivity of the method. 

USE In molybdenum determination by spectrophotometry [6964] in uranium determination by spectrophotometry [6965]. 

A circular TLC spectrophotometric method for the determination of lanthanum and yttrium at concentration level of 0.01 to 1.0% in molybdenum-based alloys has also been developed. It involves the separation of lanthanum and yttrium on cellulose layers impregnated with 0.2-Mtrioctylamine using aqueous HCl as developer, extraction from sorbent layer, and determination by spectrophotometry [69]. 

Of course, not all dissolved ions produce colored solutions, and therefore not all ions in solution can be quantified by colorimetry. Noncolored solutions can sometimes, however, be converted to colored solutions by introducing chromophore species which complex with (i.e., attach themselves to) the target ion to produce a colored solution, which may then be measured by UV/visible colorimetry. An important archaeological example of this is the determination of phosphorus in solution (which is colorless) by com-plexation with a molybdenum compound, which gives a blue solution (see below). The term colorimetry applies strictly only to analytical techniques which use the visible region of the spectrum, whereas spectrophotometry may be applied over a wider range of the electromagnetic spectrum. 

Keywords Molybdenum (VI), 3-hydroxy-2- [-3- (4-methoxyphenyl)-l-phenyl-4-pyrazolyl]-4 -oxo - 4H-1-benzopyran, solvent extraction, spectrophotometry, determination... 

Heanes [97] has described a method for determining copper, manganese and zinc in ashed plant extracts by flame AA spectrophotometry after cobalt and molybdenum have been assayed on separate aliquots of the same plant extracts by a spectrophotometric procedure [102]. (See Sect. 7.34.3). Ashing aids were necessary to maintain accuracy in the determinations. Concentrations of up to 3.5% m/m of silicon and calcium and 4% m/m of chlorine in the plants did not affect the determinations, but in some instances lower concentrations were determined in plant samples containing equal or higher levels of both added silica and calcium. 

D7. David, D. J., The determination of molybdenum by atomic-absorption spectrophotometry. Analyst 86, 730-740 (1961). 

A procedure for the determination of molybdenum in serum, red blood cells, and urine is described. The low concentration of molybdenum in most unexposed individuals requires the sensitivity obtained using atomic absorption spectrophotometry and electrothermal atomization. Spike recovery tests indicate that low temperature ashing is required for accuracy. Severe matrix interferences preclude wet ashing or high-temperature ashing as sample pretreatments. Using the method described, it is possible to distinguish between industrially exposed and unexposed individuals. 

Molybdenum has been determined by BPR in the presence of poly(vinylpyrollidone) e = 7.5 10" ) [66]. A high increase in sensitivity can be obtained by the use of 3 order derivative spectrophotometry. 

L.C.R. Pessenda, A.O. Jacintho, E.A.G. Zagatto, Catalytic determination of molybdenum in plants by flow-injection spectrophotometry with ion-exchange separation, Anal. Chim. Acta 214 (1988) 239. 

F. J. Krug, 0. Bahia F, and E. A. G. Zagatto, Determination of Molybdenum in Steels by Flow Injection Spectrophotometry. Anal. Chim. Acta, 161 (1984) 245. 

Curtis, P. R., and Grusovin, J. (1985). Determination of molybdenum in plant tissue by graphite furnace atomic absorption spectrophotometry (GFAAS). Commun. Soil Sci. Plant Anal. 16 1279-91. 

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]. 

Silicate Molybdenum blue ICP-AES Spectrophotometry 0.14-1,4mg Si detectors for the determination of orthophosphate and total phosphorus Addition of masking agents... 

Spectrophotometric determination is performed using UV-visible spectrophotometry with formation of yellow saturated silicomolybdate. The method is used normally for determination of 0.002-1 mg of Si02- For greater sensitivity (for 0.0001-0.25 mg of SiOz), the yellow silicomolybdate may be reduced with sodium sulfite or a mixture of citric and ascorbic acids (the solution must contain 5% citric acid and 1% ascorbic acid) to the corresponding silico-molybdenum blue. 

Phosphorus-containing species This is one of the major nutrients in waters. It usually comes from fertilization, detergents, and animal and plant decay. Excess phosphorus and other nutrients in sewage are responsible for eutrophication. The most recommended method for its determination is spectrophotometry after formation of the molybdophosphate heteropolyacid and reduction to molybdenum blue. 

Alkan, M. Kharun, M. Chmilenko, F. Spectrophotometrie determination of molybdenum with Alizarin Red S in the presence of poly(sulfonylpiperidinylmethylene hydroxide). Talanta 2003, 59, 605-611. 

A. Varghese, A.M.A. Khadar, and B. Kalluraya. Simultaneous determination of titanium and molybdenum in steel samples using derivative spectrophotometry in neutral micellar medium. Spectrochimica Acta Part A 64 383-390, 2006. 

Note In determination of molybdenum (molybdenum complex) [6866] for determination of tungsten by spectrophotometry [6867],... 

If the nonionic surfactant is extracted from water into an organic solvent as its potassium tetrathiocyanatozincate(II) complex, its original concentration can be related to the concentration of zinc in the extract, as determined by atomic absorption spectrometry (117) or visible spectrophotometry (118). The gravimetric barium chloride/molybdophosphoric acid method for determination of nonionics has also been adapted to an atomic absorption finish, with the residual molybdenum being determined in the supernate after centrifugation (45). Similarly, the bismuth in the barium/ethoxylated surfactant/tetraiodobismuthate precipitate can be determined by AAS (52). This procedure is discussed with gravimetric analysis. 

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