Phosphomolybdic complex

In a recent paper, Lozano-Calero and colleagues describe a new method for the quantitative analysis of phosphorus in cola beverages. The method is based on the formation of an intensely blue-colored phosphomolybdate complex,... 

This ammonium phosphomolybdate complex is yellow, but if mildly reduced by ascorbic acid in the presence of potassium antimonyl tartrate a solution of stable bluish-purple color ( molybdenum blue ) develops after about ten minutes, which has its strongest absorption at 882 pm (Fig. 4.6). Other mild reducing agents have also been used, including tin(II) chloride, or hydrazine sulfate, which give maximum absorbances at slightly different wavelengths. The intensity of the color which develops is linearly proportional to the... 

The phosphorus content can be determined by wet oxidation of the starch with sulfuric (or nitric) acid and hydrogen peroxide followed by colorimetric estimation of the phosphomolybdate complex. A detailed procedure for gravimetric determination can be found in AACC method 40-57 (AACC, 2000). However, large sample sizes (2-5 g) are required in this method. 

Spectrophotometric evaluation at 880 nm of the phosphomolybdate complex has been used to determine phosphates at pH 8.5 in soil [58]. 

The cycling and availability of P in estuaries is largely dependent on P specia-tion. Consequently, total P has traditionally been divided into total dissolved P and total particulate P fractions, which can be further divided into dissolved and particulate organic P and dissolved and particulate inorganic P pools. Another defined fraction within the TP pool is reactive phosphorus, which has been used to describe the potentially bioavailable P. Much of the work to date has focused on the soluble reactive P, which is characterized as the P fraction that forms a phosphomolybdate complex under acidic conditions. 

Soluble reactive phosphorus (SRP) the P fraction which forms a phosphomolybdate complex under acidic conditions. 

Alkaloids (e.g. brucine, strychnine) Mo Extract phosphomolybdate complex into MIBK 119-122... 

All widely used methods for serum inorganic phosphate are based on the reaction of phosphate ions with ammonimn molybdate to form a phosphomolybdate complex that is then measured by a spectrophotometer. 

The colorless phosphomolybdate complex is measured directly by ultraviolet absorption (340 nm), or reduced to molybdenum blue and measured at 600 to 700 An... 

Many reducing agents have been used for producing the blue phosphomolybdate complex, including aminonaph-tholsulfonic acid, stannous chloride, methyl-p-aminophenol sulfate, ferrous ammonium sulfate, ascorbic acid, and N phenyl-p-phenyldiamine (semidine) Each of these... 

Serum and heparinized plasma are the preferred specimens for the measurement of phosphate. Concentrations of inorganic phosphate are about 0.2 to 0.3 nig/dL (0.06 to 0.10 mmol/L) lower in heparinized plasma than in serum. Anticoagulants such as citrate, oxalate, and EDTA interfere with formation of the phosphomolybdate complex. 

As previously mentioned, phosphorus compounds are commonly classified into orthophosphates (PO ), acid-hydrolysable (condensed) phosphates and organic phosphates. It must be noticed that acid-hydrolysable phosphates (as pyrophosphates) are negligible in sewage [30], The general procedure illustrated in Fig. 11 includes two main steps an indirect UV-visible measurement (PO -) and a photo-oxidation step followed by a UV-visible measurement (Pgl)- First, orthophosphates are determined by spectrophotometric measurement of a phosphomolybdate complex (formed with addition of ammonium molybdate 40 gL-1) using the spectrum deconvolution method. 

The measurement of orthophosphates is possible from the phosphomolybdate complex formation. A base of reference spectra has been used with spectra corresponding to molybdate solution (2.4 g/L) and to the phosphomolybdate complex obtained from 10 mg/L of orthophosphate. Notice that in this case the use of a simple multicomponent procedure may be sufficient. The quantification is carried out between 380 and 450 nm. The orthophosphate concentration is given by the product of the phosphomolybdate complex coefficient by the concentration of the corresponding reference spectrum. 

Table 8 displays the results for the determination of the orthophosphate concentration from the photo-oxidation of various P-containing compounds. The molybdate solution (1.5 ml) is introduced in the reactor in order to follow the phosphomolybdate complex formation. The conversion yields are quantitative (Table 8) using irradiation time no longer than 15 min. 

The separation of phosphohydrox5dmino acids by h.p.l.c. has been described. A very sensitive method for the determination of inorganic phosphate has been described which is based on the formation of a Rhodamine B-phosphomolybdate complex, and the continuous enzsmiic removal of inorganic phosphate from reactions has been achieved by means of the nucleoside phosphorylase-catalysed phosphorolysis of nicotinamide riboside, when the product is ribose 1 -phosphate. ... 

Phosphorus is analyzed by atomic absorption and ICP emission spectrometry and neutron activation techniques. The total phosphorus contents can be estimated colorimetrically by classical wet methods (American Public Health Association... 1995). Phosphorus is oxidized to orthophosphate by digesting with potassium persulfate. The solution is treated with ammonium molybdate and antimony potassium tartarate in an acid medium to form an antimony-phosphomolybdate complex that is reduced by ascorbic acid to form a deep blue coloration, the intensity of which is proportional to the concentration of phosphorus. The absorbance is measmed at 650 nm by a spectrophotometer. Alternatively, it can be analyzed colorimetrically by an autoanalyzer (Technicon model). 

Nitrate reduction by partially purified enzyme preparations is frequently stimulated by phosphate. This has been attributed to the requirement of a phosphomolybdate complex for the reduction process (Nicholas and Stevens, 1955). The purified enzyme fromNeurospora crassa has been estimated... 

Reactions which liberate inorganic phosphate [125]. The reaction is stopped by the addition of 5 M sulphuric acid followed by 5 M sodium molybdate. The phosphomolybdate complex is then extracted into 0.2 ml of isobutanol using a vortex mixer followed by centrifugation. An aliquot (0.1 ml) of the separated upper phase is then taken for scintillation counting. 

Insoluble salts, for example, hydrous zirconium phosphate Heteropolyacids, for example, ammonium phosphomolybdate Complex ferrocyanides, for example, sodium copper cyanoferrate (II)... 

The total phenolic content of plant extracts is usually determined by colorimetric method using Folin Ciocalteu reagent. This method entails oxidation of the phenolate ion coupled to the reduction of the phosphotungstic-phosphomolybdic reagent [6, 83, 84]. The chromophore produced is a blue phosphotungstic-phosphomolybdic complex which has a maximum absorption in the region of 750 nm [22, 85]. The total phenolic content is expressed as the number of equivalents of gallic acid, tannic acid, or caffeic acid used for the calibration curves. 

The blue phosphomolybdic complex, being a colloid, has a tendency to stick as a thin film on the walls of a cuvette. This film can be removed by rinsing with dilute sodium or potassium hydroxide solutions followed by a thorough rinse with water. 

For the determination of phosphate in the presence of arsenic, the arsenate ion is reduced with thiosulphate to arsenite which does not form complexes with molybdate. Arsenate up to 3 timoVL is quantitatively reduced within 15 min. The blue phosphomolybdic complex is developed using the reagents given in Section 10.2.5.4. Calibration must be performed as described because thiosulphate reduces the colour of the blue phosphorus complex by ca. 10 %. Range and precision are the same as for the main procedure. 

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