Dilute Phosphoric Acid Solution Research Articles

A Novel Skeletal Drug-Delivery System Using Self-Setting Calcium Phosphate Cement. 3. Physicochemical Properties and Drug-Release Rate of Bovine Insulin and Bovine Albumin

A novel drug-deliver device based on a self-setting bioactive cement formed from tetracalcium phosphate and dicalcium phosphate has been developed and tested in vitro using bovine insulin and bovine albumin as model polypeptide drugs. Equimolar mixtures of the calcium phosphate powders containing bovine insulin and bovine albumin were transformed into a hydroxyapatite cement after being mixed with a dilute phosphoric acid solution. X-ray diffraction and FT-IR spectra results suggested that the raw materials transformed into lower crystallinity of hydroxyapatite as it hardened. In vitro drug release from cement pellets into a 0.1 mol/L phosphate buffer at pH 7.40 and 37 degrees C continued for more than 3 weeks. Release from the drug-loaded cements followed the Higuchi model equation.

Changes in the solubility of enamel mineral at various stages of porcine amelogenesis.

The solubility of enamel mineral (a carbonated apatite) formed at various stages of porcine amelogenesis was investigated at controlled partial pressures of CO2. Enamel samples were obtained from the outer (young) secretory, inner (old) secretory, early (soft) and late (hard) mature enamel of the permanent dentition of slaughtered piglets. The dissected enamel was pulverized and subjected to a plasma ashing at low temperature to remove organic matter. The composition (Ca, total P, HPO4, and CO3) of the enamel mineral was determined chemically. The enamel mineral contained significant amounts of carbonate and acid phosphate; the model adopted for its stoichiometry was [Ca]5-x [HPO4]v[CO3]w[PO4]3-x[OH]1-x. Each enamel sample was equilibrated in dilute phosphoric acid solutions (0.01-1.2 mM) under Pco2 = 1.86 and 1.75%. Equilibration of the enamel samples usually took 20-25 days; the solution composition (pH, concentrations of Ca, P, Mg, Na, and K, and activity of Ca2+) was determined periodically. The composition of the solution at equilibrium showed that (1) the outer (younger) secretory mineral was the most soluble and the solubility of enamel mineral decreased with advancing developmental stages; (2) the mean activity product in the saturated solutions for the outer secretory enamel was the same as that calculated on the basis of the reported composition of the enamel fluid; and (3) the solubility data obtained with most of the enamel samples were consistent with a model in which the equilibration includes two processes: dissolution of the original enamel mineral and precipitation of a new carbonatoapatite. Analyses of the equilibrated samples, particularly the mature enamel, by electron microscopy, supported the precipitation of carbonatoapatite.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of hydroxyapatite dissolution in acetic, lactic, and phosphoric acid solutions.

The present study was undertaken in an attempt to relate the kinetics of hydroxyapatite dissolution to solution parameters, under experimental conditions relevant to the dental caries process. Thus, the dissolution of hydroxyapatite was studied in acetic, lactic, and dilute phosphoric acid solutions having initial pH values from 4 to 6. Rates of dissolution and the corresponding degree of saturation with respect to hydroxyapatite were determined at various times throughout the dissolution process. Rates of dissolution of all solutions were found to decrease with increasing degree of solution saturation and were greater in solutions with lower initial values of pH. However, rates of dissolution in partially saturated phosphoric acid solutions (without added organic acid) were at least one order of magnitude lower than those observed in the organic acid buffers with the same initial pH, over the same range of saturation values. The data obtained are consistent with a surface-controlled dissolution model in which the rate of dissolution is dependent upon the degree of saturation and the sum of the activities of the acidic species in solution, i.e., phosphoric and organic acids. These results suggest that in order to assess the cariogenic potential of a given medium (e.g., plaque fluid), one must determine both the degree of saturation with respect to the dissolving mineral and the activities of acidic species in solution.

Comparative solubility study of human dental enamel, dentin, and hydroxyapatite

The solubility properties of hydroxyapatite (HA) are compared with those of human dental enamel and dentin. The apatites used in this study were equilibrated with dilute phosphoric acid solutions in CO2-containing atmospheres. The experimental results are interpreted in terms of solubility models which consider the biological materials as either HA or carbonatoapatites. Both in the HA and the dental mineral systems, the results are consistent with the precipitation of another carbonate-containing apatitic phase during equilibration. However, although the chemical behavior of the HA systems is in very good agreement with predictions based on the solubility models, the results with the bioapatites are not; this inconsistency is more marked for dentin than for enamel but in both cases the results clearly indicate the inadequacy of assuming for these dental apatites the stoichiometry of HA. The models and the experimental results show that, in principle, it is possible to define the two dental minerals in terms of respective solubility product constants, if independent information is attained on the stoichiometry of these bioapatites.

Photochemical etching of n-InP as a function of temperature and illumination

Photochemical (PC) etching of n-InP using an Ar+ laser and dilute phosphoric acid solutions was studied as a function of temperature, power, illumination frequency, and duty cycle. The etch rate was found to be independent of time and to increase fourfold by increasing temperature from 20 to 50 °C with an activation energy ≳0.34 eV. Thus the process is found to be reaction rate limited. The etch rate was observed to increase with power for low-power levels and then saturate near an irradiance of 200 W/cm2 at 20 °C. The photoetch rate, i.e., the etch rate divided by the fraction of time the Ar+ light is on, was affected by illumination duty cycle but not chopping frequency in the range 100–3200 Hz. These results are explained based on a rate equation model for material removal. Finally, a new application for PC etching is presented: sample preparation for transmission electron microscopy.

REMOVAL OF CADMIUM BY ANION EXCHANGE IN A WET PHOSPHORIC ACID PROCESS. PART 2: EQUILIBRIA, KINETICS AND REGENERATION

ABSTRACT The removal of cadmium by anion exchange from 55 w% H3PO4 (black acid from a Nissan H process) at 90°C in the presence of small amounts of halides (Cl-, Br-, I-) was investigated. Cadmium distribution coefficients, [CD]resin/[CD]acid (concentrations in mol/1), larger than 250 were obtained with HBr equilibrium concentrations of more than 0.10 w% in the phosphoric acid solution or with HI concentrations of more than 150 ppm. The regeneration of the Cd loaded resin was performed with a very dilute phosphoric acid solution (< 1 w% H3PO4). The excess of iodide in the phosphoric acid solution could also be- removed by anion exchange. A value of about 90 was obtained for the iodide distribution coefficient of a weakly basic resin. This resin could be regenerated with an 1 M NH3 solution at 50°C. The rate of adsorption and desorption of both cadmium and iodide were mainly determined by the diffusion in the resin|particle. Effective diffusivities of about 3*10-13 mZ/s and 1.3*10-11mZ/s were obtained for ...

Improved reagents for firing distance determination

Abstract Modification of reagents used in the Walker test for firing distance determination are described. These modifications increase the color intensity and sharpness of the reacted gunpowder residues, thus improving the sensitivity of the test. In this new method, the diazotization and color coupling reaction is performed by sulfanilamide and N-(1-raphthyl)ethelenediamine in a dilute phosphoric acid solution. It is thus possible to avoid a quite concentrated acetic acid solution used in the traditional method, which is unpleasent to work with.

Some chemical properties of powdered titanium carbides in their homogeneity range

A study was made of the reactions of powdered titanium carbides in their homogeneity range with dilute sulfuric, hydrochloric, and phosphoric acid solutions. It was established that the chemical properties of a titanium carbide depend to a large extent on its composition. With rise in carbon content the chemical stability of titanium carbides grows. The chemical stability of these carbides is determined by the strength of the M-C bond. With rising proportion of M-C bonds the chemical stability of titanium carbides increases. The decomposition of titanium carbides by acids possessing no oxidizing properties is accompanied by the separation of amorphous carbon in the colloidal state.

Rapid separation of urinary acids by high-performance liquid chromatography

Over a hundred acidic urinary constituents were separated within 30 min by using 5-μm octadecyl-silica columns and gradient elution with increasing acetonitrile concentration in dilute aqueous phosphoric acid solution at 70°. The column effluent was monitored with a UV detector at 280 nm or with a fluorescence detector at 260 nm excitation and 340 nm emission wavelengths. The high sensitivity and speed of analysis, the excellent reproducibility and adequate resolution obtained suggest that this technique may be useful to obtain metabolic profiles in routine clinical work.

Extraction of phosphoric acid with long-chain tertiary amines—I: Extraction from aqueous phosphoric acid solutions

The extraction of phosphoric acid from its aqueous solutions with the long-chain tertiary amine Alamine 336 in toluene was studied at 25°C. Alamine 336 is intermediate in its extraction properties between trioctylamine and tridecylamine, but the spread in the distribution coefficients between these two does not exceed 10%. Admixing 20% by volume of dodecane with the toluene diluent produces a notable synergistic effect, but high concentrations of the aliphatic diluent lead to third phase formation. Some amine is extracted from the organic phase into dilute aqueous phosphoric acid solutions, affecting the titration of this acid with base. The distribution data can be quantitatively explained by the formation in the organic phase of two amine phosphate species with stoichiometries R3N:H3PO4 of 1 : 1 and 1 : 2. At high acid concentrations (> 4.2 M), excess acid over the 1 : 2 species is extracted.

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Solubility equilibrium constant of α-hopeite

The saturation curve for synthetic α-hopeite, Zn 3(PO 4) 2·4H 2O in dilute phosphoric acid solutions has been determined at 25°C as a function of pH. Interpretation of the data in terms of a model which assumes the formation of the ion-pairs ZnHPO 4 0 and ZnH 2PO 4 + in these solutions resulted in the solubility product constant for α-hopeite of 10 −35.3±0.1. The data show that the formation of hopeite may influence both the availability of zinc in soils and the zinc levels in natural water systems.

Solubility of CaHPO4 · 2H2O and Formation of Ion Pairs in the System Ca(OH)2- H3PO4 - H2O at 37.5 °C.

The solubility isotherm for CaHPO4 · 2H2O (DCPD) in the three-component system Ca(OH)2 - H3PO4 - H2O was determined in the pH range 3.5 to 6.8 by leaching a thermostated column of DCPD with dilute phosphoric acid solutions. In confirmatory experiments, equilibrium was approached both from super- and under-saturation by shaking DCPD with appropriate solutions. The calculated ionic activity product (Ca++) × ( ), appeared to be a parabolic function of pH with a minimum near pH 5.0. The pH dependence of the ionic product could be accounted for by considering the ion pairs [CaHPO4]° and [CaH2PO4]+ as semi-empirical parameters. Under the condition of saturation with respect to DCPD, the activity of the pair [CaHPO4]° must be a constant. The activity of the species [CaH2PO4]+ was shown to vary directly with hydrogen ion activity. The activities of the two ion pairs were adjusted to give a set of pH-independent ionic activity products with a mean of 2.19±0.011 × 10-7. The stability constants for [CaHPO4]° and [CaH2PO4]+ are 5.88±0.031 × 102 and 7.49 ±0.039, respectively. Experiments were conducted to study the hydrolysis of DCPD to more basic calcium phosphates and the kinetics of these transformations is discussed. The significance of the ion pairs in human serum is considered.

The Isolation and Properties of Some Soluble Proteins From Wool V. The Isolation of the High-Sulphur Protein Scmkb2

A protein fraction almost-devoid -of lysine and histidine and comparatively poor in arginine has been, separated from the S.carhoxymethyl derivatives of the high-sulphur proteins of :Mel'ino wool. The purification wa,;.; carried ~ut in throe stages: fractional precipitation by salting-out from dilute phosphoric acid solution, fractional precipitation at 'pH 6 ,with ammonium sulphate, and finally column chromatography at pH 8�6 on DEAE�cellulose. The protein is rich in S-carboxymethyl cysteine, serine, threonine, and proline. It has been isolated from three samples of l\ierino wool.

Die vorgänge bei der gewinnung von uran aus phosphorsäure

Uranium is extracted very rapidly from phosphoric acid solutions by octyl pyro phosphoric acid diluted with n-hexan. From dilute phosphoric acid solutions, high distribution coefficients are observed, whereas from concentrated solutions low distribution coefficients. Decreasing the hydrogen ion concentration from equally concentrated phosphate solutions increases greatly the distribution coefficients. These facts as well as the other experimental results, as changing the distribution coefficient by changing the phosphoric acid concentration and the uranium concentration in the aqueous phase, or through changing the quantity of the solvent are thoroughly discussed. The different factors influencing the distribution coefficients are attributed to the different uranyl phosphate complexes existing in the aqueous phase with respect to the pH and the phosphoric acid concentration, and a complex between the uranyl ion and the solvent in the organic phase.

Stability of Dicalcium Phosphate Dihydrate in Aqueous Solutions and Solubility of Octocalcium Phosphate

AbstractThe hydrolysis of dicalcium phosphate dihydrate, CaHPO4·2H2O, in dilute phosphoric acid solutions and in water was investigated at 25° C. in the absence of CO2. Octocalcium phosphate, Ca4H(PO4)3·3H2O, was found to precipitate when the pH of the solution was higher than 6.38. The extent of the hydrolysis was larger the higher the initial pH of the solution. The solution composition followed the metastable solubility isotherm for dicalcium phosphate dihydrate until a singular point between octocalcium phosphate and dicalcium phosphate dihydrate was reached. At this point the solution had a pH of 6.38 and Ca and P concentrations of 1.36 × 10‐3M and 2.21 × 10‐3M, respectively. The solubility product of octocalcium phosphate was calculated to be (Ca)4(H)(PO4)3 = 1.25 × 10‐47.Relative rates of solution and precipitation of both dicalcium and octocalcium phosphates are discussed. No formation of anhydrous dicalcium phosphate or hydroxyapative was detected in equilibrations for as long as 90 days, even though both of these compounds are more stable than dicalcium phosphate dihydrate under the experimental conditions.