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B.w. Darvell - One of the best experts on this subject based on the ideXlab platform.
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solubility of Dicalcium Phosphate Dihydrate by solid titration
Caries Research, 2009Co-Authors: H.-b. Pan, B.w. DarvellAbstract:Solid-titration results for hydroxyapatite (HAp), octacalcium Phosphate, beta-tricalcium Phosphate and tetracalcium Phosphate have shown that the only stable phase in 100 mmol x l(-1) KCl at 37 degrees C is HAp. In particular, Dicalcium Phosphate Dihydrate (DCPD) did not form at pH <4.2 (where it is otherwise believed to be stable) except as a metastable phase under conditions of slight supersaturation. The behaviour of DCPD itself under the same conditions requires checking. Solid titration was used to determine the apparent solubility of DCPD in a 100-mmol x l(-1) KCl solution at 37.0 +/- 0.1 degrees C over the pH range 3.2-11.6. The constitution of the precipitate was determined by X-ray diffraction, particle morphology was observed by scanning and transmission electron microscopy, and the precipitate Ca/P ratio was calculated by energy-dispersive X-ray analysis. The titration curve for DCPD was substantially lower than the position reported elsewhere. DCPD was the only identified phase at equilibrium at pH 3.60 and 4.50, but HAp was formed after seeding with 1 mg HAp at DCPD equilibrium at pH 4.47, 3.60 and 3.30. It is concluded that the titration curve observed for DCPD corresponds to the solubility isotherm for the phase, but that this represents a metastable equilibrium. HAp is more stable than DCPD, particularly below pH 4.2. The implications for calcium Phosphate studies are profound as the reverse is generally believed to be true. Thus, solubility results and the nature of the carious lesion need reconsideration.
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Solubility of Dicalcium Phosphate Dihydrate by solid titration.
Caries Research, 2009Co-Authors: H.-b. Pan, B.w. DarvellAbstract:Solid-titration results for hydroxyapatite (HAp), octacalcium Phosphate, beta-tricalcium Phosphate and tetracalcium Phosphate have shown that the only stable phase in 100 mmol x l(-1) KCl at 37 degrees C is HAp. In particular, Dicalcium Phosphate Dihydrate (DCPD) did not form at pH
Matthias Leitritz - One of the best experts on this subject based on the ideXlab platform.
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Compression force/time-profiles of microcrystalline cellulose, Dicalcium Phosphate Dihydrate and their binary mixtures—a critical consideration of experimental parameters
European Journal of Pharmaceutics and Biopharmaceutics, 1997Co-Authors: Peter C. Schmidt, Matthias LeitritzAbstract:Abstract Compression force/time-profiles of microcrystalline cellulose and Dicalcium Phosphate Dihydrate and mixtures thereof were compared on a modern rotary press by three different methods of compression: compression to a constant tablet weight, compression to a constant tablet height and compression from a constant filling depth. Compression was carried out at three different compression force levels. The differences obtained by analysing the area under the curve in the compression, dwell and decompression phase could be explained by differences of the in-die working density of the powders and their respective compression behaviour. From data of the compression phase as well as from the area-quotient-index obtained from the dwell time it was possible to estimate the percolation threshold of Dicalcium Phosphate Dihydrate in a mixture with microcrystalline cellulose to ~ 50% (w/w) corresponding to 30% (v/v).
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compression force time profiles of microcrystalline cellulose Dicalcium Phosphate Dihydrate and their binary mixtures a critical consideration of experimental parameters
European Journal of Pharmaceutics and Biopharmaceutics, 1997Co-Authors: Peter C. Schmidt, Matthias LeitritzAbstract:Abstract Compression force/time-profiles of microcrystalline cellulose and Dicalcium Phosphate Dihydrate and mixtures thereof were compared on a modern rotary press by three different methods of compression: compression to a constant tablet weight, compression to a constant tablet height and compression from a constant filling depth. Compression was carried out at three different compression force levels. The differences obtained by analysing the area under the curve in the compression, dwell and decompression phase could be explained by differences of the in-die working density of the powders and their respective compression behaviour. From data of the compression phase as well as from the area-quotient-index obtained from the dwell time it was possible to estimate the percolation threshold of Dicalcium Phosphate Dihydrate in a mixture with microcrystalline cellulose to ~ 50% (w/w) corresponding to 30% (v/v).
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Compression force/time-profiles of microcrystalline cellulose, Dicalcium Phosphate Dihydrate and their binary mixtures: a critical consideration of experimental parameters
European Journal of Pharmaceutics and Biopharmaceutics, 1997Co-Authors: Peter C. Schmidt, Matthias LeitritzAbstract:Abstract Compression force/time-profiles of microcrystalline cellulose and Dicalcium Phosphate Dihydrate and mixtures thereof were compared on a modern rotary press by three different methods of compression: compression to a constant tablet weight, compression to a constant tablet height and compression from a constant filling depth. Compression was carried out at three different compression force levels. The differences obtained by analysing the area under the curve in the compression, dwell and decompression phase could be explained by differences of the in-die working density of the powders and their respective compression behaviour. From data of the compression phase as well as from the area-quotient-index obtained from the dwell time it was possible to estimate the percolation threshold of Dicalcium Phosphate Dihydrate in a mixture with microcrystalline cellulose to ~ 50% (w/w) corresponding to 30% (v/v).
H.-b. Pan - One of the best experts on this subject based on the ideXlab platform.
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solubility of Dicalcium Phosphate Dihydrate by solid titration
Caries Research, 2009Co-Authors: H.-b. Pan, B.w. DarvellAbstract:Solid-titration results for hydroxyapatite (HAp), octacalcium Phosphate, beta-tricalcium Phosphate and tetracalcium Phosphate have shown that the only stable phase in 100 mmol x l(-1) KCl at 37 degrees C is HAp. In particular, Dicalcium Phosphate Dihydrate (DCPD) did not form at pH <4.2 (where it is otherwise believed to be stable) except as a metastable phase under conditions of slight supersaturation. The behaviour of DCPD itself under the same conditions requires checking. Solid titration was used to determine the apparent solubility of DCPD in a 100-mmol x l(-1) KCl solution at 37.0 +/- 0.1 degrees C over the pH range 3.2-11.6. The constitution of the precipitate was determined by X-ray diffraction, particle morphology was observed by scanning and transmission electron microscopy, and the precipitate Ca/P ratio was calculated by energy-dispersive X-ray analysis. The titration curve for DCPD was substantially lower than the position reported elsewhere. DCPD was the only identified phase at equilibrium at pH 3.60 and 4.50, but HAp was formed after seeding with 1 mg HAp at DCPD equilibrium at pH 4.47, 3.60 and 3.30. It is concluded that the titration curve observed for DCPD corresponds to the solubility isotherm for the phase, but that this represents a metastable equilibrium. HAp is more stable than DCPD, particularly below pH 4.2. The implications for calcium Phosphate studies are profound as the reverse is generally believed to be true. Thus, solubility results and the nature of the carious lesion need reconsideration.
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Solubility of Dicalcium Phosphate Dihydrate by solid titration.
Caries Research, 2009Co-Authors: H.-b. Pan, B.w. DarvellAbstract:Solid-titration results for hydroxyapatite (HAp), octacalcium Phosphate, beta-tricalcium Phosphate and tetracalcium Phosphate have shown that the only stable phase in 100 mmol x l(-1) KCl at 37 degrees C is HAp. In particular, Dicalcium Phosphate Dihydrate (DCPD) did not form at pH
Peter C. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Compression force/time-profiles of microcrystalline cellulose, Dicalcium Phosphate Dihydrate and their binary mixtures—a critical consideration of experimental parameters
European Journal of Pharmaceutics and Biopharmaceutics, 1997Co-Authors: Peter C. Schmidt, Matthias LeitritzAbstract:Abstract Compression force/time-profiles of microcrystalline cellulose and Dicalcium Phosphate Dihydrate and mixtures thereof were compared on a modern rotary press by three different methods of compression: compression to a constant tablet weight, compression to a constant tablet height and compression from a constant filling depth. Compression was carried out at three different compression force levels. The differences obtained by analysing the area under the curve in the compression, dwell and decompression phase could be explained by differences of the in-die working density of the powders and their respective compression behaviour. From data of the compression phase as well as from the area-quotient-index obtained from the dwell time it was possible to estimate the percolation threshold of Dicalcium Phosphate Dihydrate in a mixture with microcrystalline cellulose to ~ 50% (w/w) corresponding to 30% (v/v).
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compression force time profiles of microcrystalline cellulose Dicalcium Phosphate Dihydrate and their binary mixtures a critical consideration of experimental parameters
European Journal of Pharmaceutics and Biopharmaceutics, 1997Co-Authors: Peter C. Schmidt, Matthias LeitritzAbstract:Abstract Compression force/time-profiles of microcrystalline cellulose and Dicalcium Phosphate Dihydrate and mixtures thereof were compared on a modern rotary press by three different methods of compression: compression to a constant tablet weight, compression to a constant tablet height and compression from a constant filling depth. Compression was carried out at three different compression force levels. The differences obtained by analysing the area under the curve in the compression, dwell and decompression phase could be explained by differences of the in-die working density of the powders and their respective compression behaviour. From data of the compression phase as well as from the area-quotient-index obtained from the dwell time it was possible to estimate the percolation threshold of Dicalcium Phosphate Dihydrate in a mixture with microcrystalline cellulose to ~ 50% (w/w) corresponding to 30% (v/v).
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Compression force/time-profiles of microcrystalline cellulose, Dicalcium Phosphate Dihydrate and their binary mixtures: a critical consideration of experimental parameters
European Journal of Pharmaceutics and Biopharmaceutics, 1997Co-Authors: Peter C. Schmidt, Matthias LeitritzAbstract:Abstract Compression force/time-profiles of microcrystalline cellulose and Dicalcium Phosphate Dihydrate and mixtures thereof were compared on a modern rotary press by three different methods of compression: compression to a constant tablet weight, compression to a constant tablet height and compression from a constant filling depth. Compression was carried out at three different compression force levels. The differences obtained by analysing the area under the curve in the compression, dwell and decompression phase could be explained by differences of the in-die working density of the powders and their respective compression behaviour. From data of the compression phase as well as from the area-quotient-index obtained from the dwell time it was possible to estimate the percolation threshold of Dicalcium Phosphate Dihydrate in a mixture with microcrystalline cellulose to ~ 50% (w/w) corresponding to 30% (v/v).
R.c. Rowe - One of the best experts on this subject based on the ideXlab platform.
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Chemical stability of acetylsalicylic acid in tablets prepared with different particle size fractions of a commercial brand of Dicalcium Phosphate Dihydrate
International Journal of Pharmaceutics, 1995Co-Authors: Mariana Landin, Consuelo Souto, Angel Concheiro, Ramón Martínez-pacheco, José Luis Gómez-amoza, Marta Casalderrey, R.c. RoweAbstract:Abstract The proportion of acetylsalicylic acid degraded to salicylic acid in tablets prepared with different particle size fractions of a single brand of Dicalcium Phosphate Dihydrate (DCPD), and then stored for 6 months at 35°C and 82.9% relative humidity, was linearly correlated ( r = −0.9937) with the mean particle size of the excipient. Mean particle size may therefore be a useful predictor of the chemical stability of easily hydrolysed active principles in tablets prepared with a given brand of DCPD.
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Structural changes during the dehydration of Dicalcium Phosphate Dihydrate
European Journal of Pharmaceutical Sciences, 1994Co-Authors: Mariana Landin, R.c. Rowe, Peter YorkAbstract:Abstract The crystal structure and molecular packing of Dicalcium Phosphate Dihydrate (DCPD) and Dicalcium Phosphate anhydrous (DCPA) have been investigated and compared. Major differences have been found between these materials. Water is bound to the calcium ions in the DCPD crystal lattice which collapses when water is removed to form DCPA. X-ray powder diffraction including variable temperature studies, and Fourier Transform Raman spectroscopy have been used and provide insight into the mechanism of dehydration of DCPD.
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Particle size effects on the dehydration of Dicalcium Phosphate Dihydrate powders
International Journal of Pharmaceutics, 1994Co-Authors: Mariana Landin, R.c. Rowe, Peter YorkAbstract:Abstract The particle size of Dicalcium Phosphate Dihydrate (DCPD) has a strong influence on its dehydration behaviour, specifically the weight loss in the first stage of dehydration. This weight loss has been found to be inversely proportional to the mean particle size of the samples. Mean particle size may be a useful parameter in predicting the dehydration behaviour of DCPD and is clearly a contributing factor in explaining batch and source variation.
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Dicalcium Phosphate Dihydrate for direct compression: Characterization and intermanufacturer variability
International Journal of Pharmaceutics, 1994Co-Authors: Mariana Landin, Consuelo Souto, Angel Concheiro, Ramón Martínez-pacheco, José Luis Gómez-amoza, R.c. RoweAbstract:Abstract The structure, dehydration behaviour, and particle characteristics of the two currently available commercial brands of unmilled Dicalcium Phosphate Dihydrate (DCPD) for direct compression, Emcompress and DiTab, were studied. The two brands have very similar properties, differing significantly only in intraparticle porosity. As a consequence, their compression and flow properties are effectively identical. The characteristics of Emcompress and DiTab were compared with those of two DCPD powders, Calipharm (whose properties are typical of milled DCPD preparations) and Kyowa (whose properties are in many respects atypical). It is concluded that the processing undergone by unmilled DCPD for direct compression does not cause major changes in crystal structure, mechanical and surface properties with respect to typical powders. However, there are considerable differences in dehydration behaviour, which can probably be attributed to the larger mean particle size and different particle structure of the direct compression preparations.
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The effect of country of origin on the properties of Dicalcium Phosphate Dihydrate powder
International Journal of Pharmaceutics, 1994Co-Authors: Mariana Landin, Consuelo Souto, Angel Concheiro, Ramón Martínez-pacheco, José Luis Gómez-amoza, R.c. RoweAbstract:Abstract Five brands of Dicalcium Phosphate Dihydrate powder manufactured in Germany, Japan, Spain, U.K. and U.S.A. have been characterized by X-ray diffraction, IR, DSC and TGA. Results on dehydration behaviour showed the Japanese material to be significantly more stable than the other four materials. SEM and laser scattering results showed these other four materials to be very similar, and to differ from the Japanese material, as regards micromeritic characteristics. Differences in specific surface values, as measured by adsorption of nitrogen, are related to particle size and intraparticle porosity. The above differences give rise to differences in their compression and flow properties, which could be relevant to the use of these products as excipients for solid dosage forms.