Water-extractable phosphorus

Methodological considerations for water-extractable phosphorus studies... 

Quantitation of tebuconazole residue in water extracts is also performed by the calibration technique. Construct a new calibration curve of 0.5-, 1-, 2-, and 5-mg L equivalent tebuconazole standard solutions for each set of analyses. Inject 5- o.L aliquots of the standard solutions. The injection volume should be kept constant as the peak area varies with the injection volume by nitrogen-phosphorus detection. Plot the peak area against the injected concentrations of tebuconazole. 

Sornsrivichai P, Syers JK,Tillman RW, Cornforth IS. An evaluation of water extraction as a soil-testing procedure of phosphorus. Glasshouse assessment of plant-available phosphate. Fert. Res. 1988 15 211-223. 

Tufenkji N, Elimelech M (2004) Correlation equation for predicting single-collector efficiency in physicochemical filtration in saturated porous media. Environ Sci Technol 38 529-536 Turner BL, Kay MA, Westermann DT (2004) Colloid phosphorus in surface runoff and water extracts from semiarid soils of the western United States. J Environ Qual 33 1464-1472 van Genuchten MT (1980) A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci Soc Am J 44 892-898... 

Method 6.2a. Determination of water-soiubie phosphorus (extraction)... 

Water (elemental phosphorus) Extract with organic solvent oxidize to phosphate Spectrophotometric 1.5 pg/L No data Zitko et al. 1970 Idler et al. 1981... 

Waste water (elemental phosphorus) Extract with organic solvent, oxidize to phosphate and back-extract in water Neutron activation analysis 0.01 pg/L 90-110 Lai and Rosenblatt 1977b... 

Water (elemental phosphorus) Extract with isooctane or diethyl ether GC-NPD 0.011 pg/L 107 12 Walsh 1995... 

C) Preparation of 9,10-Dihydro-4H-Benzo[4,5]Cyclohepta[l,2-b]Thiophen-(4)-One 200 ml of 85% phosphoric acid and 112 g of phosphorus pentoxide are heated to 135°C. 7.0 g of o-[2-thienyl-(2 )-ethyl]benzoic acid are then introduced while stirring thoroughly over a period of 30 min. Stirring is then continued for another hour at 135°C and the reaction mixture is then stirred into 1 liter of ice water. Extraction is then effected 3 times, using 250 ml ether portions, the ethereal extract is washed with 2 N sodium carbonate solution, dried over sodium sulfate and reduced in volume by evaporation. The residue is boiled up with 55 ml of ethanol, the solution freed of resin by decanting and then stirred at room temperature for 6 hours with animal charcoal. It is then filtered off, reduced in volume in a vacuum and the residue distilled. BP 120° to 124°C/0.005 mm, nD24-5 = 1.6559. 

To a solution of 1 gram of 16-dehydropregnenolon-3p-acetate in 10 ml pyridine is added 0.22 gram of hydroxylamine hydrochloride, and the mixture is allowed to stand at room temperature for four days. One gram of 16-dehydropregnenolon-3p-acetate oxime is dissolved in 30 ml of hot dioxane, and then the solution is cooled in an ice bath until about one-half of the dioxane has solidified. Then 1 gram of phosphorus pentachloride is added and the mixture is shaken until all the dioxane has melted. The mixture is maintained at 35°C, for seventy-five minutes, then an excess of ice is added and the solution is again allowed to stand at 35°C. After about thirty minutes, a solution of 5 ml of concentrated hydrochloric acid in 10 ml of water is added, and the mixture is diluted with water, extracted with ether and the ethereal extract washed with dilute sodium hydroxide solution. The ether is removed on a steam bath and the residue is worked up to yield dehydro-isoandrosterone. 

The most common approach to phosphorus determination is the assessment of phosphate in wet chemistry. Therefore, the majority of samples should be dissolved before analysis. Solid samples are decomposed by alkali or acid treatment silicate is dissolved by treatment with fluoric acid. Samples of biological material are reduced to ash using an appropriate laboratory oven or are digested with hot oxidative acids. A direct phosphate assessment is advised only in some water samples. The determination of total phosphoms is not used to identify soil fertility due to phosphorus content rather, water extracts are used of various pH and ionic strength. 

The deactivated catalyst was studied by several methods scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS), infrared spectroscopy (IR), and by extracting water-insoluble phosphorus. The SEM-EDS studies gave no useful results. IR absorption was measured on samples that were mulled in mineral oil. Comparisons of IR spectra were made with samples of y -alumina and aluminum phosphate. Determination of total P in the deactivated sample, presumed to be present as water-insoluble aluminum phosphate, was made by standard wet chemical analysis dissolution in hot, dilute HCl followed by colorimetric determination of phosphate. ... 

Turner, B.L., McKelvie, I.D. and Haygarth, P.M. (2002) Characterisation of water-extractable soil organic phosphorus by phosphatase hydrolysis. Soil Biology and Biochemistry 34, 29-37. 

Fig. 12.2. The increase in water-soluble organic phosphorus after soil drying as a function of soil microbial phosphorus in a wide range of permanent pasture soils from England and Wales (Turner and Haygarth, 2001). Water-soluble phosphorus was determined by extracting soils at field moisture capacity with water in a 4 1 solution/soil ratio for 1 h. Subsamples were air-dried for 7 days at 30°C and extracted in an identical manner.

It is important to note that results from phosphorus solubilization studies involving water-extraction can be markedly influenced... 

During the last decade, information on the organic phosphorus composition of soil solutions and water extracts has been obtained by phosphatase hydrolysis. This technique not only gives structural information on filterable organic phosphorus, but also indicates its potential biological availability. In solution from Scottish upland soils, up to 64% of the filterable organic phosphorus was hydrolysed by non-specific phosphatases (Shand and Smith, 1997), while hydrolysable unreactive phosphorus in water extracts of Australian pasture soils was dominated by phosphate diesters and myo-inositol hexakisphosphate (Turner et al., 2002a). Only small concentrations of labile monoesters were detected in the latter study, possibly due to the rapid hydrolysis of labile compounds by soil phosphatase enzymes. 

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