Buffers, orthophosphate

H2P04, and in Equation 7.61, P04 is the salt of the acid HP04 . So each of these pairs constitutes a buffer system, and orthophosphate buffers can be prepared over a wide pH range. The optimum buffering capacity of each pair occurs at a pH corresponding to its Ka. The HP04 /H2P04 couple is an effective buffer system in the blood (see below). 

Uses. The principal use of monosodium phosphate is as a water-soluble soHd acid and pH buffer, primarily in acid-type cleaners. The double salt, NaH2P04 H PO, referred to as hemisodium orthophosphate or sodium hemiphosphate, is often generated in situ from monosodium phosphate and phosphoric acid in these types of formulations. Mixtures of mono- and disodium phosphates are used in textile processing, food manufacture, and other industries to control pH at 4—9. Monosodium phosphate is also used in boiler-water treatment, as a precipitant for polyvalent metal ions, and as an animal-feed supplement. 

In the presynthetic surfactant era, soap was budt (and stiU is) with alkaline salts such as soda ash, sdicates, orthophosphates, and borates. These materials buffer the wash solution to a high pH and prevent soap protonation thus the soap remains effective. Another type of budder is the neutral... 

Buffers resist a change in pH when protons are produced or consumed. Maximum buffering capacity occurs 1 pH unit on either side of pAl,. Physiologic buffers include bicarbonate, orthophosphate, and proteins. 

When cyanoacetylene (5), which is produced when an electric discharge is passed through a mixture of methane and nitrogen, is dissolved in a phosphate buffer a stable enol-phosphate (6) is formed. Pyrophosphate is produced when neutral aqueous solutions of (6) and orthophosphate are heated, and the phosphorylation of UMP has been achieved. However, from a study of the rate of phosphorylation and a consideration of environmental factors, especially the likely phosphate concentration in oceans, it is suggested that (6) is not an important intermediate in prebiotic phosphorylation. The conversion of the 3 -phosphate of 0 2 -cyclocytidine (7) into 2, 3 -cyclic CMP under mild conditions in aqueous solution has... 

The most common buffering system containing a weak base together with its salt formed with a strong acid is ammonia with ammonium sulphate. Some useful buffers are obtained from combinations of unrelated acids or bases with salts. The following combinations find occasional use in textile coloration processes, but the acetates and orthophosphates are most frequently used ... 

The pyrophosphate buffer is of particular technical interest as it can be used over the relatively wide range of pH 3-9. Unlike the orthophosphate titration curve, that for the tetrabasic pyrophosphate system is almost straight [6]. This linearity (Figure 10.3) means that effective buffering action is available across the whole pH range simply by using various pairs of ionised components and varying their proportions even so, however, it does not seem to be widely used. 

Fixation in 6-12 hours with a mixture of sodium hydroxide and trisodium orthophosphate, a metering device being necessary. This method is recommended for regenerated cellulosic fibres. This formulation contains the same total amount of alkali as method (1) with the same bath stability, but may be preferred where some buffering capacity is required and sodium silicate is undesirable. 

Materials Required Plasma protein solution 2.0 ml mixed phosphate buffer pH 7.0 with azide [To 1000 ml of a solution containing 1.8% w/v of disodium hydrogen orthophosphate and 2.3% w/v of sodium chloride and sufficient of a solution containing 0.78% w/v of sodium dihydrogen orthophosphate and 2.3% w/v of sodium chloride (about 280 ml) to produce a pH of 7.0 Dissolve sufficient sodium azide in the resulting solution to give a 0.02% w/v solution] 1000 ml ... 

A metabolic status parameter (abbreviated Rp) that indicates the phosphorylating power of ATP in cells as well as the availability of ADP and orthophosphate for oxidative phosphorylation Rp = [ATP]/[[ADP][Orthophos-phate]). This ratio is buffered on the immediate time scale by substrate-level phosphorylation of ADP and on the intermediate time scale by mitochondrial phosphorylation of ATP which is then translocated to the cytoplasm and other compartments. 

In studies with alkaline phosphatase it has been found that the enzymic activity measured by the release of p-nitrophenol from p-nitrophenyl phosphate increases with the concentration of tris buffer much faster than it increases with the ionic strength of other salts such as NaCl and Mg2SO< (4, 50). This behavior of tris was shown by Dayan and Wilson (122, 123) to result from a transphosphorylation reaction, where 0.5 M tris reacts with phosphoryl enzyme to form tris phosphate at the same rate as does 55 M water to form orthophosphate. 

The chromatographic procedure may be carried out using (a) two stainless steel columns in series the first (25 cm x 4.6 mm) packed with particles of silica, the surface of which has been modified with chemically bonded hexysilyl groups (5 /im) (Spherisorb C6 is suitable) and the second (25 cm x 4.6 mm) packed with cation exchange resin (10 /an) (Partisil-10 SCX is suitable) (b) as the mobile phase at a flow rate of 1.0 ml/min, a mixture of 25 volumes of acetonitrile, 25 volumes of a phosphate buffer solution prepared by dissolving 58.5 g of sodium dihydrogen orthophosphate... 

Fig. 4.15 Chromatogram of orthophosphate, diphosphate and triphosphate. Column is p-Gondapak-NH2 and the eluant was oxalate-Mg buffer at the flow rate of 1. 0ml min-1,...

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... 

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