Metals metaphosphoric acid

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

Mercury(II) chloranilate 700 Mercury(II) nitrate standard soln. of, 359 Mercury/mercury( II )-EDTA electrode (mercury electrode) 586 potentiometric titration of metallic ions with EDTA and, 588 prepn. of, 587 Mercury thiocyanate 700 Metaphosphoric acid in homogeneous precipitation, 426 Metal apparatus 93 Metal ion buffer 53... 

The most important point during sample preparation is to prevent oxidation of ascorbic acid. Indeed, it is easily oxidized by an alkaline pH, heavy metal ions (Cu and Fe ), the presence of halogens compounds, and hydrogen peroxide. The most suitable solvent for this purpose is metaphosphoric acid, which inhibits L-ascorbic oxidase and metal catalysis, and it causes the precipitation of proteins. However, it can cause serious analytical interactions with silica-based column, e.g., C18 or amino bonded-phases [542] and it could co-elute with AA. 

Ferrous metaphosphate, Fe(P03)2, is prepared by the action of fused metaphosphoric acid on ferrous phosphate, oxalate, or chloride, or even metallic iron, at red heat in a current of carbon dioxide. The salt is obtained as a white insoluble powder, unaffected by hydrochloric or nitric acid, but attacked by hot concentrated sulphuric acid.6... 

The use of metaphosphoric acid solutions for the extraction of ascorbic acid from plant and animal tissues was first proposed in 1935 (29). Metaphosphoric acid, along with trichloroacetic acid, remain as the reagents of choice. Besides the decreased tendency for hydrolysis of the lactone ring, metaphosphoric acid inhibits the catalytic oxidation of ascorbic acid by metal catalysts, such as copper and iron ions, and it inactivates the enzymes that oxidize ascorbic acid. Oxidation of ascorbic acid, which apparently is the result of the action of oxyhemoglobin, may occur when animal tissues are ground with metaphosphoric acid. This... 

Solutions of serum-albumin are laevogyrous [a]o = —56° they are not precipitated by CO2, by acetic or phosphoric acid, by ether or by magnesium sulfate. They are precipitated by mineral acids, tannic acid, metaphosphoric acid, and most metallic salts. When heated they become opalescent at 60° (140° P.), and coagulate in the flocculent form at 72°-75° (161°.6-167° F.). 

The nse of a high ionic strength acidic extraction solvent is required to suppress metabolic activity upon disrnption of the cell and to precipitate proteins. A metal chelator snch as ethylenediaminetetraacetic acid (EDTA) is also usually required. The use of metaphosphoric acid is the best way to extract and stabilize L-ascorbic acid, as suggested by various authors [72,78,80,81]. For this reason, the samples were extracted with 3% metaphosphoric acid-8% acetic acid-1 mM EDTA solution, which is known to limit L-ascorbic acid degradation to less than 5% [82]. 

Metal refining in metallurgy, the purification of a metal. (133) Metaphosphoric acids acids with the general formula (HP03) . (22.7)... 

AA is susceptible to both chemical and enzymatic oxidation [1]. Chemical oxidation is catalyzed by minerals, such as Cu(II) and Fe(III), in the presence of oxygen at a pH-dependent rate enzymatic oxidation by the ascorbate oxidase occurring in plant tissues. Light and heat are other factors that promote its degradation. For these reasons, the extraction procedure should be designed to stabilize the vitamin for example, metaphosphoric acid [63—66] denatures proteins, inactivates enzymes, provides a medium below pH 4 (degradation rate is minimal at pH 2), and inhibits metal catalysis, whereas EDTA [67,68] chelates the minerals efficiently. 

Phosphoric acid gives no precipitate with ordinary salts of the metals whose sulfides are soluble in 0.3-M HCl (in the case of Fe , a distinction from di- and metaphosphoric acids) but does form precipitates with Ag" and Pb ". Concentrated H3PO4, however, does not precipitate Ag. ... 

PHOSPHORIC ACID H,PO. While phosphoric acid, OrthophoBi ork add, 15% Phosphoric acid, Metaphosphoric add Strong cMistks, most metals Not combustible ... 

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