Phosphorus fractionation scheme

Modified simple sequential inorganic phosphorus fractionation schemes include (1) extraction of soil with neutral salt such as KCl, NaCl, or NH4CI, followed by (2) residual soil extraction with... 

The forms of phosphorus in sediments and soils can be operationally defined by chemical extraction schemes. The major inorganic phosphorus components are considered to comprise those (i) adsorbed by exchange sites (ii) associated with iron, aluminium and manganese oxides (iii) associated with carbonate (iv) associated with calcium as apatite or (v) bound in a crystalline mineral form (e.g. silicates). The organic phosphorus fraction, on the other hand, is either considered as a whole, or operationally divided... 

Cross, A.F. and Schlesinger, W.H. (1 995) A literature review and evaluation of the Medley fractionation scheme applications to the biogeochemi-cal cycle of soil phosphorus in natural ecosystems. Geoderma 64, 1 97-21 4. 

The early fractionation schemes (Chang and Jackson, 1957) developed for terrestrial agricultural soils grouped soil phosphorus into (i) phosphorus present as orthophosphate ions sorbed onto the surface of P-retaining components (nonoccluded P), (ii) phosphorus present within the matrices of P-retaining components (occluded P), and (iii) phosphorus present in discrete phosphate minerals such as apatite. 

M NaOH. The residual soil after alkali extraction is treated with 0.5 M HCl to dissolve Ca- and Mg-bound P (Figure 9.11a) (Reddy et al., 1998b). A few examples of inorganic phosphorus forms determined by chemical fractionation scheme follow. 

The relative bioavailability of inorganic phosphorus in wetland soils (Figure 9.15) as determined by chemical fractionation scheme can be summarized as follows ... 

The SEDEX procedure has emerged as the benchmark extraction scheme for sediments. It uses only magnesium chloride, acetate buffeg and citrate/di-thionite-bicarbonate reagents at pH values between 4 and 8 to leach sediments of the inorganic associated phosphorus fractions before ashing at 550°C and a final extraction with 1M HCl to determine the so-called residual organic phosphorus. 

Fractionation of milk and titration of the fractions have been of considerable value. Rice and Markley (1924) made an attempt to assign contributions of the various milk components to titratable acidity. One scheme utilizes oxalate to precipitate calcium and rennet to remove the calcium caseinate phosphate micelles (Horst 1947 Ling 1936 Pyne and Ryan 1950). As formulated by Ling, the scheme involves titrations of milk, oxalated milk, rennet whey, and oxalated rennet whey to the phenolphthalein endpoint. From such titrations, Ling calculated that the caseinate contributed about 0.8 mEq of the total titer of 2.2 mEq/100 ml (0.19% lactic acid) in certain milks that he analyzed. These data are consistent with calculations based on the concentrations of phosphate and proteins present (Walstra and Jenness 1984). The casein, serum proteins, colloidal inorganic phosphorus, and dissolved inorganic phosphorus were accounted for by van der Have et al (1979) in their equation relating the titratable acidity of individual cow s milks to the composition. The casein and phosphates account for the major part of the titratable acidity of fresh milk. 

The diastereoselective nucleophilic addition to vinylphosphonates containing an asymmetric phosphorus atom (306) has been reported. Fractional crystallisation of the diastereoisomeric mixture of products affords a diastereomerically pure sample of (307). The relative configuration of major diastereoisomers were confirmed by X-ray crystallography (Scheme 82). ... 

For the activation of phospholipid with AMBH, a maleimide derivative of phosphatidyiethanolamine, 7, is prepared using SMCC (Scheme 2). In brief, phosphatidyiethanolamine, 6, in chloroform was reacted with 1.5 molar excess of SMCC, 5, over lipid in presence of 5 molar excess of TEA under argon for 5 h. The maleimide-derivative is separated from excess SMCC on silica gel column using chloroform methanol (4 0.2 v/v) mobile phase. The elution fractions containing Ninhydrin-negative and phosphorus-positive fractions are pooled and concentrated under reduced pressure. DOPE-... 

Phosphorus is not a TE but a major nutrient element. Nevertheless, fractionation of this element is essential for environmental studies, and hence it seems reasonable to highlight here some relevant SEPs. Four different procedures for the fractionation of P in lake sediment samples have been tested in an interlaboratory study in the framework of the SM T program (Ruban et al., 1999). As a result, a novel scheme based on the Williams protocol (Williams et al., 1976) has been developed aimed at the restoration of lake sediments. The scheme comprises three separate assays (1) sequential extraction of NaOH-extractable (Fe- and Al-bound) and HCl-extractable (Ca-bound) fractions, (2) sequential extraction of inorganic and organic phosphorus and (3) single extraction, after calcination, of concentrated HCl-extractable (total P) fraction (see Table 12.3 for further details). Further discrimination of specific compounds is made feasible by the use of chromatographic and capillary separation techniques as reviewed by Spivakov et al. (1999). 

Phosphorus in sediments can be divided into several different fractions according to chemical separation methods. Williams et al. (1976) outlined a scheme of three fractions apatite-P, organic P, and... 

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