Inorganic phosphate quantitative analysis

While there have been a considerable number of structural models for these multinuclear zinc enzymes (49), there have only been a few functional models until now. Czamik et al. have reported phosphate hydrolysis with bis(Coni-cyclen) complexes 39 (50) and 40 (51). The flexible binuclear cobalt(III) complex 39 (1 mM) hydrolyzed bis(4-nitro-phenyl)phosphate (BNP-) (0.05 mM) at pH 7 and 25°C with a rate 3.2 times faster than the parent Coni-cyclen (2 mM). The more rigid complex 40 was designed to accommodate inorganic phosphate in the in-temuclear pocket and to prevent formation of an intramolecular ju.-oxo dinuclear complex. The dinuclear cobalt(III) complex 40 (1 mM) indeed hydrolyzed 4-nitrophenyl phosphate (NP2-) (0.025 mM) 10 times faster than Coni-cyclen (2 mM) at pH 7 and 25°C (see Scheme 10). The final product was postulated to be 41 on the basis of 31P NMR analysis. In 40, one cobalt(III) ion probably provides a nucleophilic water molecule, while the second cobalt(III) binds the phosphoryl group in the form of a four-membered ring (see 42). The reaction of the phosphomonoester NP2- can therefore profit from the special placement of the two metal ions. As expected from the weaker interaction of BNP- with cobalt(in), 40 did not show enhanced reactivity toward BNP-. However, in the absence of more quantitative data, a detailed reaction mechanism cannot be drawn. 

The ubiquitous nature and broad importance of phosphates demands exacting analytical methods for their characterization. Phosphorus-31 nuclear magnetic resonance ( P NMR) has been used as a method for the quantitative analysis of small inorganic phosphates (1-4). Several potential advantages are offered by "P NMR including observation of only the phosphorus-containing species, structural information which may complement or aid Retired... 

Phosphorus in starch is found in different forms, mainly starch phosphate monoester, phospholipids, and inorganic phosphate. 31P NMR spectroscopy was used to identify each of these forms in alpha-dextrins prepared from starches of different sources.128 Quantitative analysis was possible in DMSO solution. 

Card JK, Card DR, and Callis CF (1992) Quantitative analysis of inorganic phosphates using NMR spectroscopy. In Walsh EN, Griffith EJ, Parry RW, and Quin ED (eds.) Phosphorus Chemistry, Developments in American Science. Washington, DC American Chemical Society. 

Naturally occurring lipid mixtures have a composition of such extreme complexity that the analysis by chemical methods of a group of these substances or the determination of a single compound in such mixtures, appears hopeless. Up to about ten years ago, lipid mixtures were characterised by totals like acid-, saponification-, iodine-, thio-cyanogen- and diene- numbers . The determination of the amount of non-saponifiable matter after alkaline hydrolysis was a standard method in the analysis of fats. Phospholipids and sulpholipids were quantitatively determined as inorganic phosphate and sulphate after combustion. These methods were supplemented by detection of subsidiary fat constituents like lipochromes, sterols and resin acids, with the help of colour reactions. 

Miscellaneous applications of phosphates have included use of porphysome nanoparticles as a nontoxic alternative to inorganic nanocrystals for the efficient conversion of light into heat in photothermal therapy, fluorescent phosphates for qualitative and quantitative analysis of organophosphates in water and simultaneous differentiation and quantitative analysis of a methylphosphonate (a nerve gas byproduct) and glyphosate. 

The analysis of phosphates and phosphonates is a considerably complex task due to the great variety of possible molecular structures. Phosphorus-containing anionics are nearly always available as mixtures dependent on the kind of synthesis carried out. For analytical separation the total amount of phosphorus in the molecule has to be ascertained. Thus, the organic and inorganic phosphorus is transformed to orthophosphoric acid by oxidation. The fusion of the substance is performed by the addition of 2 ml of concentrated sulfuric acid to — 100 mg of the substance. The black residue is then oxidized by a mixture of nitric acid and perchloric acid. The resulting orthophosphate can be determined at 8000 K by atom emission spectroscopy. The thermally excited phosphorus atoms emit a characteristic line at a wavelength of 178.23 nm. The extensity of the radiation is used for quantitative determination of the phosphorus content. 

---