Orthophosphates, determination

In the Murphy and Riley [85] method 10ml of demineralized water and 2ml of concentrated nitric acid were added to 0.15-0.2g of dry sediment (predried at 103°C) or plant material in a 100ml Erlenmeyer Flask. After a preliminary oxidation by evaporation of water and nitric acid on a hot plate, 2ml of concentrated perchloric acid were added, and the sample was boiled until clear. After cooling, the sample was diluted to 100 ml and an aliquot was withdrawn for orthophosphate determination by the ascorbic acid reduction method of Murphy and Riley [85]. Blanks and standards were treated as samples. 

Orthophosphates, determination of, in mixtures of phosphates, 3 93 Orthophosphoric acid, 1 101 Orthophosphoric acid-D3, 6 81... 

Table 7. Characteristics of the UV method for orthophosphates determination (without...

The amount of orthophosphate which could be recovered from a sample seemed to depend largely on how long and how vigorously the sample was shaken during the analysis. It appeared that orthophosphate which was either adsorbed on or associated with the sediment was being released into solution. Since it was also found that sahnity variations affected color development and that large turbidity corrections that were necessary when samples high in suspended sohds were analyzed, it was decided that only a soluble orthophosphate determination was possible. 

In most analytical procedures for determining the total phosphoms content (normally expressed in terms of P20 ), the phosphates are converted to the orthophosphate form. Typically, condensed phosphates are hydrolyzed to orthophosphate by boiling in dilute mineral acid (0.1 N). The orthophosphate is then deterrnined by gravimetric or spectrophotometric methods. For gravimetric deterrnination, insoluble phosphomolybdates (or magnesium ammonium orthophosphate) is formed. 

The general manufacturing scheme for phosphate salts is shown in Figure 11. Condensed phosphates are prepared from the appropriate orthophosphate or mixture of orthophosphates, so the preparation of orthophosphates must be considered first for the manufacture of any phosphate salt. Phosphoric acid is neutralized to form a solution or slurry with a carefully adjusted acid/base ratio according to the desired orthophosphate product. The orthophosphate may be recovered either by crystallization from solution, or the entire solution or slurry may be evaporated to dryness. The dewatering (qv) method is determined by the solubihty properties of the product and by its desired physical properties such as crystal size and shape, bulk density, and surface area. Acid orthophosphate salts may be converted to condensed phosphates by thermal dehydration (calcination). 

We developed a sensor for determination of content of phosphorars in metallurgical melts. In quality of ion conductor used orthophosphate of calcium which pressed in tablets 010 mm. Tablets (mass 1-2 g) annealed at a temperature 400°C during 7-10 h. Tablets melts then in a quartz tube and placed the alloy of iron containing 1 mass % P. Control of sensor lead on Fe - P melts. Information on activities (effective concentration) of phosphorars in Fe - P melts was received. It is set that the isotherm of activity of phosphorars shows negative deviations from the Raouls law. Comparison them with reliable literary inforiuation showed that they agree between itself. Thus, reliable data on activities (effective concentration) of phosphorars in metallic melts it is possible to received by created electrochemical sensor for express determination. 

Phosphorus from organophosphorus compounds, which are combusted to give mainly orthophosphate, can be absorbed by either sulphuric acid or nitric acid and readily determined spectrophotometrically either by the molybdenum blue method or as the phosphovanadomolybdate (Section 17.39). 

The method may be standardised, if desired, with pure potassium dihydrogen-orthophosphate (see below) sufficient 1 1 hydrochloric acid must be present to prevent precipitation of quinoline molybdate the molybdophosphate complex is readily formed at a concentration of 20 mL of concentrated hydrochloric acid per 100 mL of solution especially when warm, and precipitation of the quinoline salt should take place slowly from boiling solution. A blank determination should always be made it is mostly due to silica. 

The method can be applied to the determination of phosphorus in a wide variety of materials, e.g. phosphate rock, phosphatic fertilisers and metals, and is suitable for use in conjunction with the oxygen-flask procedure (Section 3.31). In all cases it is essential to ensure that the material is so treated that the phosphorus is converted to orthophosphate this may usually be done by dissolution in an oxidising medium such as concentrated nitric acid or in 60 per cent perchloric acid. 

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. 

Eberlein and Kattner [194] described an automated method for the determination of orthophosphate and total dissolved phosphorus in the marine environment. Separate aliquots of filtered seawater samples were used for the determination orthophosphate and total dissolved phosphorus in the concentration range 0.01-5 xg/l phosphorus. The digestion mixture for total dissolved phosphorus consisted of sodium hydroxide (1.5 g), potassium peroxidisulfate (5 g) and boric acid (3 g) dissolved in doubly distilled water (100 ml). Seawater samples (50 ml) were mixed with the digestion reagent, heated under pressure at 115-120 °C for 2 h, cooled, and stored before determination in the autoanalyser system. For total phosphorus, extra ascorbic acid was added to the aerosol water of the autoanalyser manifold before the reagents used for the molybdenum blue reaction were added. For measurement of orthophosphate, a phosphate working reagent composed of sulfuric acid, ammonium molyb-... 

Several investigators have described the indirect determination of orthophosphate by extraction of the phosphomolybdic acid complex and the measuring the molybdenum extracted. Zaugg and Knox 2921 first applied this technique to the determination of phosphate in urine. A protein-free filtrate was formed and the complex was extracted into 2-octanol. More recently, Devoto 293) determined 0 to 25 pg of phosphate in 50 ml of urine by extracting the complex from acidified urine into isobutyl acetate. 

Organic phosphorus is determined by the difference in phosphorus content of the 1M hydrochloric acid extract measured before and after ignition of the dry sediments at 550°C. In all instances the orthophosphate is determined by using standard Technicon AutoAnalyzer II techniques. Silica does not interfere. 

The determination of the orthophosphate was carried out by using the automated systems described by the Technicon Instruments Corporation. The manifolds used are shown in Fig. 12.3. The procedures referred to below as methods I and II are Technicon industrial methods Nos. 94-70W and 155-71W, respectively. Method I includes ascorbic acid alone for the reduction of the molybdophosphoric acid whereas in method II the mixed reagents ascorbic acid, sulphuric acid, ammonium molybdate and antimony potassium tartrate are used. Method I is intended for use for high levels of phosphorus (up to lOpg ml4) and method II for low levels (less than 0.5pg ml4). The wetting agent (Levor IV) used in order to obtain a smooth bubble pattern, is present in the ascorbic acid reagent line for method I whereas it is added externally Fig. 12.3) in the water line (0.5pg ml4 of Levor) in method II. 

Dry sediment (0.15-0.2g) was ignited in a muffle furnace in a porcelain crucible (550°C for lh). After cooling, the residue was washed into a 100ml Erlenmeyer flask with 25ml mol L-1 hydrochloric acid and boiled for 15min on a hot plate. The sample was diluted to 100ml and orthophosphate was determined as in the perchloric acid method. Standards and blanks were not ignited. 

Determination of total phosphorus in lake sediments by ignition of samples in a muffle furnace at 550°C, boiling of the residue from ignition in lmol L 1 hydrochloric acid, and subsequent determination of orthophosphate gave approximately the same values as the perchloric acid digestion. 

The whole column, apart from a small portion of the sediment, is sam pled in this way. The chemical checks were carried out every 15 days, determining pH, Conductivity, C.O.D., Ammoniacal Nitrogen, Orthophosphate Phosphorus and, furthermore, each month Total phosphorus, Total Kjeldahl Nitrogen, Total Solids and Volatile Solids. The methods utilized are those indicated in the Standard Methods (A.P.H.A., 1980). The amount of matter particles sedimented in the tanks was estimated with the use ol appropriate sampling devices located at the bottom of the tanks and withdrawn after a variable permanence of 40 to 60 days. 

Phosphorus is a common component of additives and appears most commonly as a zinc dialkyl dithiophosphate or triaryl phosphate ester, but other forms also occur. Two wet chemical methods are available, one of which (ASTM D1091) describes an oxidation procedure that converts phosphorus to aqueous orthophosphate anion. This is then determined by mass as magnesium pyrophosphate or photochemically as molybdivanadophosphoric acid. In an alternative test (ASTM D4047), samples are oxidized to phosphate with zinc oxide, dissolved in acid, precipitated as quinoline phosphomolybdate, treated with excess standard alkali, and back-titrated with standard acid. Both of these methods are used primarily for referee samples. Phosphorus is most commonly determined using x-ray fluorescence (ASTM D4927) or ICP (ASTM D4951). 

Determination of Orthophosphate in Estuarine and Coastal Waters by Automated Colorimetric Analysis... 

In both schemes, the specificities of the pump for catalysis change in the two enzyme states. Jencks points out that coupling is determined (a) by the chemical specificity achieved in catalyzing phosphoryl transfer to and from the enzyme (wherein E-Ca2 reversibly binds ATP, and E reacts reversibly with orthophosphate), and (b) by the vectorial specificity for ion binding and dissociation (wherein E reversibly binds/dissociates cytoplasmic calcium ion, and E—P reversibly binds/dissociates luminal calcium). There must be a single conformation change during the reaction cycle between Ei and E2 in the free enzyme and from Ei P-Ca2 to E2-P-Ca2 after enzyme phosphorylation. 

Procedure. Pipette 1 ml of the AOAC extract (increase appropriately if the peaks are too small) into a 20-ml volumetric flask. Using a pipettor, carefully add 1 ml H SO (approximately 98% m/m), swirl slowly to mix and allow to cool. Make up to the mark with 50% (v/v) H SO (approximately 98% m/m), stopper and invert several times to mix. The water soluble P, present in the sample solution as orthophosphate, can be determined by autoanaiysis see Chapter 7 for details of standards, reagents and method. 

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