Vitreous phosphates

In this paper we deal with complexes in which the donor atom is exclusively oxide(—II). Such complexes include aquo complexes, which are well documented, and oxyanion complexes such as phosphato, borato, etc. which are present in vitreous phosphates, borates, etc. and in anhydrous oxyacids. We therefore are dealing with complexes, of metal ions M , comprising a system which can be written schematically as... 

The most generally prepared vitreous phosphates, the sodium polyphosphate glasses (1.5 > NajO-PjOs > 1.00), are made by dehydration and melting of acid salts or their mixtures in platinum (again avoiding reducing substances), e.g. ... 

Dental silicate cement was also variously known in the past as a translucent, porcelain or vitreous cement. The present name is to some extent a misnomer, probably attached to the cement in the mistaken belief that it was a silicate cement, whereas we now know that it is a phosphate-bonded cement. It is formed by mixing an aluminosilicate glass with an aqueous solution of orthophosphoric acid. After preparation the cement paste sets within a few minutes in the mouth. It is, perhaps, the strongest of the purely inorganic cements when prepared by conventional methods, with a compressive strength that can reach 300 MPa after 24 hours (Wilson et al, 1972). 

Takamura et al. have reported an electrochemical method for the determination of chlorpromazine with an anodically pretreated vitreous carbon electrode [164]. Optimal conditions for the pre-treatment were attained by the anodic oxidation of vitreous carbon electrodes in 0.5 mM phosphate buffer (pH 6.7) at 1.6 V V5. S.C.E. for 2 minutes. This was found to enhance the oxidation peak of the cyclic voltammogram for chlorpromazine by a factor of simeq 30. The peak current at +0.75 V was directly proportional to the concentration of chlorpromazine over the range of 0.2-40 pM and the detection limit was 0.1 pM. 

Takamura et al. have reported a voltammetric method for the determination of chlorpromazine using an anodically oxidized carbon electrode [167]. A vitreous-carbon electrode was maintained at +1.6 V vi. S.C.E. for 2 minutes (in 0.5 M phosphate buffer at pH 6.8). Under these conditions, chlorpromazine gave an oxidation peak current on cyclic voltammograms that varied linearly with concentration over the range of 50 nM to 1 pM. 

Takamura et al. have determined chlorpromazine by the use of differential pulse voltammetry incorporating rotating glassy-carbon disc electrodes [170]. The determination was carried out after pre-treatment of vitreous carbon by anodic oxidation for two minutes in 0.5 M phosphate buffer (pH 6.3) at 1.6 V vs. Ag/AgCl reference electrode. The determination was made with the use of 50 mV pulses at 2 seconds intervals, a rotation rate of 2500 rpm, and a scan rate of 5 mV/sec. 

TRIPHYLITE. This mineral is a phosphate of lithium and ferrous iron, LiFePC>4. It crystallizes in the orthorhombic system, but usually is characterized by large clcavablc masses. The hardness is 4.5-5.0 specific gravity, 3.42-3.56, vitreous lo resinous luster, translucent, and bluegray color. The mineral occurs as a rare primary mineral in granitic pegmatites and. when available in large quantities, is a source of lithium. Worldwide occurrences include Bavaria, Finland, Sweden, and in the United States, New Hampshire. Maine, and South Dakota. 

Dichloroaniline, 2,4-dimethyl-aniline HPLC-ED. Vitreous working electrode and Ag/AgCl reference electrode. Applied voltage 0.9-1.0 V. p-Bondapak C-18 stationary phase. Mobile phase phosphate buffer (pH = 6.0) and ACN. 

Some physical properties of metaphosphoric acid.—Metaphosphoric acid is a transparent, vitreous solid sometimes called glacial phosphoric add. E. Brescius2 said that the glacial acid is soft and flexible, and the presence of sodium phosphate makes it hard. The commercial acid is sold in sticks, and, according to A. Betten-dorff, it often contains some sodium salts and some ortho- and pyro-acids as impurities. The dry acid deliquesces rapidly in air, and it readily dissolves in water with the development of much heat. The acid solidifies to a vitreous mass without crystallization from solutions with less than 63 per cent, of water. 

Fig. 7.3 Dependence of the current density on the overvoltage for electrodes rotating at 500 rpm (top curve) and 1,000, 2,000, and 4,000 rpm (bottom curve) under 1 atm O2 at 37°C. Scan rate 5 mV s 1. Left polished Pt in O.5MH2SO4. Right wired billirubin oxidase (BOD) on polished vitreous carbon in a pH 7.2 saline (0.15M NaCl) phosphate (0.02 M) buffer. The wired BOD film, loaded at 0.17 mg cm-2, comprised 32.3 wt% BOD, 60.2 wt% redox polymer, and 7.5 wt% PEGDGE (adapted from Mano, 2003)...

Hastings et al. [55] used this same in vitro technology to assess the enhancement delivery of dexamethasone using the Visulex iontophoretic system. The Visulex applicator and a freshly excised rabbit sclera were positioned between two halves of a side-by-side diffusion cell with the conjunctival side of the sclera facing the applicator (Figure 26.10). The donor drug solution (1 mg of dexamethasone phosphate) was present in the applicator, and diluted vitreous humor was modeled in the receptor cell. One milliampere direct current was applied for 60 min, and samples were collected during different treatment periods. It was demonstrated that the Visulex system produced a twofold increase in the amount of dexamethasone phosphate delivered after 60 min, compared with a standard iontophoretic administration (without the Visulex applicator). 

A BASJ ion-exchange microbore column (45 cm x 1 mm i.d.) 0.05 Sodium phosphate buffer of pH 8.5 containing 0.1 mM EDTA [60 pL/min]. Electrochemical at horseradish peroxidase osmium redox polymer-modified vitreous C electrodes at 0 mV versus Ag/AgCl. Rat frontal cortex dialysate samples [188]... 

Sodium metaphosphate, NaPOs.—The metaphosphate is prepared by the interaction of sodium nitrate and phosphoric acid at 330° C.20 It is a white, vitreous mass, almost insoluble in water, and melting21 at 617 2° C. It is sometimes called Maddrell s salt, after its discoverer.22 The semihydrate, NaP03, H20, is formed by heating sodium ammonium hydrogen phosphate at 160° to 170° C., and subsequently raising the temperature to 320° C.23 Tammann24 has proved the existence... 

Rapid cooling of phosphate melts gives vitreous materials in which no long-range order is present, but with similar local environments and connectivity of phosphate tetrahedra... 

Vitreous P2O5 and phosphate-rich glasses are difficult to prepare, owing to the volatility of P2O5, and are very moisture sensitive. Vibrational and MASNMR spectra show that they contain three-dimensional phosphate networks comparable to those in the extended forms of P2O5 and ultraphosphates. 

Nd-doped phosphate glasses are also used in a variety of high-gain or high-power laser applications. These materials are typically metaphosphate glasses such as NaPOs or A1(P03)3 containing <1% Nd. Vitreous NdPsO can also be used. 

One study compared vitreous and serum concentrations after 7.5-mg oral doses of dexamethasone with peribulbar injections of 5 mg dexamethasone phosphate. Peribulbar administration of the agent resulted in 3.9% higher intravitreal than vitreous concentrations, but serum dexamethasone levels were approximately equal with both routes of administration. 

Constitution of Phosphate Glasses. CH. 4 of Modem-Aspects of the Vitreous State (J. D. Mackenzie, ed.). New York Butterworths 1960. 

Composite materials are mechanical dispersions of radioactive solids, for instance ciystalline or vitreous radioactive phases in metal matrix [24], glass-encapsulated Ca-phosphate based ceramics [30] glass-bonded sodalite [31,32] glass-ceramics for plutonium waste immobilization [33] and so on. 

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