Phosphate, absorption

Samples of animal bones weighing approximately 3 g are ashed at 600 °C until the entire bone is ash-white. Samples are then crushed in a mortar and pestle. A portion of the sample is digested in HCl and diluted to a known volume. The concentrations of zinc and strontium are determined by atomic absorption. The analysis for strontium illustrates the use of a protecting agent as La(N03)3 is added to prevent an interference due to the formation of refractory strontium phosphate. 

Description of Method. The water-soluble vitamins Bi (thiamine hydrochloride), B2 (riboflavin), B3 (niacinamide), and Be (pyridoxine hydrochloride) may be determined by CZE using a pH 9 sodium tetraborate/sodlum dIhydrogen phosphate buffer or by MEKC using the same buffer with the addition of sodium dodecyl-sulfate. Detection Is by UV absorption at 200 nm. An Internal standard of o-ethoxybenzamide Is used to standardize the method. 

Indicators There are certain compounds that are suitable as indicators for sensitive and specific clinical analysis. Nicotinamide adenine dinucleotide (NAD) occurs in oxidized (NAD" ) and reduced (NADH) forms. Nicotinamide adenine dinucleotide phosphate (NADP) also has two states, NADP" and NADPH. NADH has a very high uv—vis absorption at 339 nm, extinction coefficient = 6300 (M cm) , but NAD" does not. Similarly, NADPH absorbs light very strongly whereas NADP" does not. 

The amount of each element required in daily dietary intake varies with the individual bioavailabihty of the mineral nutrient. BioavailabiUty depends both on body need as deterrnined by absorption and excretion patterns of the element and by general solubiUty, and on the absence of substances that may cause formation of iasoluble products, eg, calcium phosphate, Ca2(P0 2- some cases, additional requirements exist either for transport of substances or for uptake or binding. For example, calcium-binding proteias are iavolved ia calcium transport an intrinsic factor is needed for vitamin cobalt,... 

One method of treatment is to inject calcitonin, which decreases blood Ca " concentration and increases bone calcification (33). Another is to increase the release of calcitonin into the blood by increasing the blood level of Ca " ( 4). This latter treatment is accompHshed by increasing Ca " absorption from the intestine requiring dietary calcium supplements and avoidance of high phosphate diets. The latter decrease Ca " absorption by precipitation of the insoluble calcium phosphate. 

Fig. 3. Infrared absorption data for the four tricresyl phosphate isomers present in hydrauHc oil. a, Trimetacresyl phosphate b, metametaparacresyl phosphate c, metaparaparacresyl phosphate d, triparacresyl phosphate. The P=0 stretch between 1300 and 1350 cm is marked as is the phenyl—phosphate vibration around 965 cm . Also included are the metacresyl (875 cm ) and paracresyl (820 cm ) frequencies.

Hydroxy vitamin D pools ia the blood and is transported on DBF to the kidney, where further hydroxylation takes place at C-1 or C-24 ia response to calcium levels. l-Hydroxylation occurs primarily ia the kidney mitochondria and is cataly2ed by a mixed-function monooxygenase with a specific cytochrome P-450 (52,179,180). 1 a- and 24-Hydroxylation of 25-hydroxycholecalciferol has also been shown to take place ia the placenta of pregnant mammals and ia bone cells, as well as ia the epidermis. Low phosphate levels also stimulate 1,25-dihydtoxycholecalciferol production, which ia turn stimulates intestinal calcium as well as phosphoms absorption. It also mobilizes these minerals from bone and decreases their kidney excretion. Together with PTH, calcitriol also stimulates renal reabsorption of the calcium and phosphoms by the proximal tubules (51,141,181—183). 

Although it is being found that vitamin D metaboUtes play a role ia many different biological functions, metaboHsm primarily occurs to maintain the calcium homeostasis of the body. When calcium semm levels fall below the normal range, 1 a,25-dihydroxy-vitainin is made when calcium levels are at or above this level, 24,25-dihydroxycholecalciferol is made, and 1 a-hydroxylase activity is discontiaued. The calcium homeostasis mechanism iavolves a hypocalcemic stimulus, which iaduces the secretion of parathyroid hormone. This causes phosphate diuresis ia the kidney, which stimulates the 1 a-hydroxylase activity and causes the hydroxylation of 25-hydroxy-vitamin D to 1 a,25-dihydroxycholecalciferol. Parathyroid hormone and 1,25-dihydroxycholecalciferol act at the bone site cooperatively to stimulate calcium mobilization from the bone (see Hormones). Calcium blood levels are also iafluenced by the effects of the metaboUte on intestinal absorption and renal resorption. 

Hardness can also be calculated by summation of the individually deterrnined alkaline earths by means of atomic absorption analysis. Basic samples must be acidified, and lanthanum chloride must be added to minimise interferences from phosphate, sulfate, and aluminum. An ion-selective electrode that utilizes ahquid ion exchanger is also available for hardness measurement however, this electrode is susceptible to interferences from other dissolved metal ions. 

Dutch State Mines (Stamicarbon). Vapor-phase, catalytic hydrogenation of phenol to cyclohexanone over palladium on alumina, Hcensed by Stamicarbon, the engineering subsidiary of DSM, gives a 95% yield at high conversion plus an additional 3% by dehydrogenation of coproduct cyclohexanol over a copper catalyst. Cyclohexane oxidation, an alternative route to cyclohexanone, is used in the United States and in Asia by DSM. A cyclohexane vapor-cloud explosion occurred in 1975 at a co-owned DSM plant in Flixborough, UK (12) the plant was rebuilt but later closed. In addition to the conventional Raschig process for hydroxylamine, DSM has developed a hydroxylamine phosphate—oxime (HPO) process for cyclohexanone oxime no by-product ammonium sulfate is produced. Catalytic ammonia oxidation is followed by absorption of NO in a buffered aqueous phosphoric acid... 

Disopyr mide. Disopyramide phosphate, a phenylacetamide analogue, is a racemic mixture. The dmg can be adininistered po or iv and is useful in the treatment of ventricular and supraventricular arrhythmias (1,2). After po administration, absorption is rapid and nearly complete (83%). Binding to plasma protein is concentration-dependent (35—95%), but at therapeutic concentrations of 2—4 lg/mL, about 50% is protein-bound. Peak plasma concentrations are achieved in 0.5—3 h. The dmg is metabolized in the fiver to a mono-AJ-dealkylated product that has antiarrhythmic activity. The elimination half-life of the dmg is 4—10 h. About 80% of the dose is excreted by the kidneys, 50% is unchanged and 50% as metabolites 15% is excreted into the bile (1,2). 

Liquid Dispersion Spray columns are used with slurries or when the reaction product is a solid. The absorption of SO9 by a hme slurry is an example. In the treatment of phosphate rock with sulfuric acid, offgases contain HF and SiF4. In a spray column with water, solid particles of fluorosilic acid are formed but do not harm the spray operation. The coefficient /cl in spray columns is about the same as in packed columns, but the spray interfacial area is much lower. Considerable backmixing of the gas also takes place, which helps to make the spray volumetri-caUy inefficient. Deentrainment at the outlet usually is needed. 

Phosphate fertilizer complexes often have sulfuric and phosphoric acid production facilities. Sulfuric acid is produced by burning molten sulfur in air to produce sulfur dioxide, which is then catalytically converted to sulfur trioxide for absorption in oleum. Sulfur dioxide can also be produced by roasting pyrite ore. Phosphoric acid is manufactured by adding sulfuric acid to phosphate rock. The... 

Fig. 1 A) Separation of phosphates and phosphonic acids B) absorption plots of track 5 and track 8. PjOl (1), PjOio (2), P20t (3), POl (4), mixture 1 (5), aminotrimethylene-phosphonic acid (6), l-hydroxyethane-l,l-diphosphonic acid (7), mixture II (8).

Vitamin D is a family of closely related molecules that prevent rickets, a childhood disease characterized by inadequate intestinal absorption and kidney reabsorption of calcium and phosphate. These inadequacies eventually lead to the demineralization of bones. The symptoms of rickets include bowlegs,... 

The most important uses for phosphate coatings entail sealing with oil or paint and it is therefore of interest to study absorption values. Table 15.9 compares the absorption of diacetone alcohol into coatings of widely differing thicknesses and composition despite these differences, values of 10-8-12-9g/m are obtained throughout. It is therefore evident that absorption is predominantly a surface effect and not appreciably influenced by coating thickness. 

Spectrophotometric methods may often be applied directly to the solvent extract utilising the absorption of the extracted species in the ultraviolet or visible region. A typical example is the extraction and determination of nickel as dimethylglyoximate in chloroform by measuring the absorption of the complex at 366 nm. Direct measurement of absorbance may also be made with appropriate ion association complexes, e.g. the ferroin anionic detergent system, but improved results can sometimes be obtained by developing a chelate complex after extraction. An example is the extraction of uranyl nitrate from nitric acid into tributyl phosphate and the subsequent addition of dibenzoylmethane to the solvent to form a soluble coloured chelate. 

Molybdenum blue method. When arsenic, as arsenate, is treated with ammonium molybdate solution and the resulting heteropolymolybdoarsenate (arseno-molybdate) is reduced with hydrazinium sulphate or with tin(II) chloride, a blue soluble complex molybdenum blue is formed. The constitution is uncertain, but it is evident that the molybdenum is present in a lower oxidation state. The stable blue colour has a maximum absorption at about 840 nm and shows no appreciable change in 24 hours. Various techniques for carrying out the determination are available, but only one can be given here. Phosphate reacts in the same manner as arsenate (and with about the same sensitivity) and must be absent. 

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