Molybdate reactive phosphorus

Transport of contaminants by surface runoff is illustrated in the experimental results of Turner et al. (2004), which deal with the colloid-mediated transfer of phosphorus (P) from a calcareous agricultural land to watercourses. Colloidal molybdate-reactive phosphorus (MRP) was identified by ultrafiltration associated with particles between l am and Inm in diameter. Colloidal P compounds can constitute a substantial component of the filterable MRP in soil solution and include primary and secondary P minerals, P occluded or adsorbed on or within mineral or organic particles, and biocolloids (Kretzschmar et al. 1999). 

Table 12.4 Colloidal (1pm - Inm) and dissolved (

Molybdate-reactive phosphorus in the autotrophic subsystem and in the return flow between the decomposer and autotrophic subsystems... 

For many scientists involved in the analysis of phosphorus in water, sediment and soil, the only available techniques depend on the colorimetric determination of molybdate-reactive phosphorus, and that which can be made reactive during a digestion step. Molybdate-reactive phosphorus in filtered samples is generally equated to inor-... 

Shan et al. (1994) used alkaline phosphatase from Escherichia coli in immobilized enzyme reactors in a flow injection analysis system to perform rapid on-line enzymatic hydrolysis of organic phosphorus and detection of the released phosphate as molybdate-reactive phosphorus. This approach has several advantages compared with the conventional batch reaction approach ... 

The organic phosphorus content of solutions is generally determined by the difference between total phosphorus and molybdate-reactive phosphorus. As this fraction may also contain condensed phosphates (Ron Vaz etal., 1993), the operational term molybdate-unreactive phosphorus is used throughout the chapter, rather than organic phosphorus, which is used in a generic sense. 

Haygarth, P.M., Ashby, C.D. and Jarvis, S.C. (1995) Short-term changes in the molybdate reactive phosphorus of stored soil waters. Journal of Environmental Quality 24, 11 33-1 1 40. 

Haygarth, P.M., Warwick, M.S. and House, W.A. (1997) Size distribution of colloidal molybdate reactive phosphorus in river waters and soil solution. Water Research 31,439 42. 

Determination of the condensed phosphorus component requires hydrolytic conditions without oxidation, and is typically achieved by boiling samples with 0.05 M sulfuric acid for 90 min or autoclaving for 30 min, prior to determination as molybdate reactive phosphorus. 

Anion exchange chromatography and ion exchange chromatography have been used extensively for the separation and quantitation of condensed phosphates. Because phosphate is a poor UV chro-mophore, direct UV detection cannot be used, and fraction collection for subsequent acid hydrolysis and detection as molybdate reactive phosphorus (MRP)... 

Phosphorus and Silicon in Waters, Effluents and Sludges [e.g. Phosphorus in Waters, Effluents and Sludges by Spectrophotometry-phosphomolybdenum blue method. Phosphorus in Waters and Acidic Digests by Spectrophotometry-phosphovanadomolybdate method. Ion Chromatographic Methods for the Determination of Phosphorus Compound, Pretreatment Methods for Phosphorus Determinations, Determination of silicon by Spectrophotometric Determination of Molybdate Reactive Silicon-1 -amino-2-naphthol-4, sulphonic acid (ANSA) or Metol reduction methods or ascorbic acid reduction method. Pretreatment Methods to Convert Other Eorms of Silicon to Soluble Molybdate Reactive Silicon, Determination of Phosphorus and Silicon Emission Spectrophotometry], 1992... 

Cambella and Antia [385] determined phosphonates in seawater by fractionation of the total phosphorus. The seawater sample was divided into two aliquots. The first was analysed for total phosphorus by the nitrate oxidation method capable of breaking down phosphonates, phosphate esters, nucleotides, and polyphosphates. The second aliquot was added to a suspension of bacterial (Escherichia coli) alkaline phosphatase enzyme, incubated for 2h at 37 °C and subjected to hot acid hydrolysis for 1 h. The resultant hot acid-enzyme sample was assayed for molybdate reactive phosphate which was estimated as the sum of enzyme hydrolysable phosphate and acid hydrolysable... 

The chemical form of phosphorus in the water column available for uptake by biota is important. The biologically available phosphorus is usually taken to be soluble reactive phosphorus (orthophosphate) , i.e. which, upon acidification of a water sample, reacts with added molybdate to yield molybdophosphoric acid, which is then reduced with SnCl2 to the intensely-coloured molybdenum blue complex and is determined spectrophotometrically (Imax = 882 nm). Reduction in inputs of phosphate, for example from point sources or by creating water meadows and buffer strips to contain diffuse runoff, has obviously been one of the major approaches to stemming eutrophication trends and... 

The phosphorus concentration in each operationally defined fraction is typically detected using the phosphomolybdate-blue colorimetric reaction and spectrophoto-metric detection (American Public Health Association, 1995), with or without pre-treatment and/or filtration. The term total phosphorus applies to samples subjected to hydrolysis and/or oxidation pretreatment intended to convert all forms of phosphorus to phosphate (Maher and Woo, 1998 Monaghan and Ruttenberg, 1999). Phosphorus that reacts with molybdate in untreated samples is referred to as reactive phosphorus . Samples may be unfiltered or filtered. When samples are unfiltered, the operationally defined fractions are total... 

Phosphorus species that are determined in this manner are referred to as molybdate reactive, or simply reactive, and much of the nomenclature of phosphorus speciation derives from this origin. 

Table 1 Specification scheme for phosphorus (P) based on determination of molybdate reactive (R), phosphorus in total (T), filterable (F), and particulate (P) forms O and C designate organic and condensed forms, respectively...

Operational classification of physicochemical forms of phosphorus in waters, based on filtration, digestion method, and molybdate reactivity. 

Tarapchak, S.J., Soluble reactive phosphorus measurements in lake water Evidence for molybdate-enhanced hydrolysis. Journal of Environmental Quality 12,105,1983. 

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