Search Results

You are looking at 51 - 60 of 314 items for :

  • "recrystallization" x
  • All content x
Clear All
Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Chatterjee, S. Bhattacharyya, A. Bhattacharyya, M. Banerjee, G. Muthukrishnan, and S. Banerjee

Abstract  

A method is described for the recovery of NH4 99TcO4 from its reaction waste. From the collected waste solution99Tc was precipitated as99Tc2S7 which on digestion with ammoniacal hydrogen peroxide produced a mixture of NH4 99TcO4 and (NH4)2SO4 from which the latter was removed by treatment with Ba(OH)2. The solution fumished NH4 99TcO4 as a crystalline material in 54% overall yield and with 96–98% purity after chromatographic purification over Dowex 50W column. Recrystallisation of this material from aqueous ammoniacal ethanol gave the analytical material which compared well with a standard sample and with literature data in terms of its -counts/mg and its molar extinction co-efficients () at 244 and 286 nm.

Restricted access

Abstract  

The thermal behaviour of binary mixtures between β-cyclodextrin (β-CD) and either carbamazepine polymorphic Form I (CBZ I), Form III (CBZ III) or dihydrate was investigated in order to assess possible interactions of CBZ solid phases with β-CD. Physical mixtures and kneaded binaries of β-CD and different CBZ crystal forms were studied by differential scanning calorimetry, thermogravimetric analysis and hot stage microscopy. The pattern of transition of CBZ Form III into Form I is strongly influenced by β-CD. The liquid-solid transition is practically absent when anhydrous CBZ/β-CD mixes are tested, as a consequence of an interaction between β-CD and liquid CBZ that hinders CBZ recrystallisation as Form I occurring after CBZ Form III melting. Water loss on heating of CBZ dihydrate in the presence of β-CD leads in all cases to the formation of CBZ Form I.

Restricted access

Abstract  

The compound BR-A657 is an angiotensin II receptor antagonist. The objective of this work was to investigate the existence of polymorphs and pseudopolymorphs of BR-A657 and the transformation of crystal forms. Three crystal forms of BR-A657 have been isolated by recrystallization and characterized by powder X-ray diffractometry, differential scanning calorimetry, and thermogravimetric analysis. After storage of three days at 0% RH (silica gel, 20°C), 52% RH (saturated solution of Na2Cr2O7·2H2O/20°C) and 95% RH (saturated solution of Na2HPO4/20°C), Forms 2 and 3 were transformed to Form 1.

Restricted access

Abstract  

Temperature-modulated DSC (TMDSC) was used to enhance the perfection of crystals of different poly(p-phenylene sulfide) samples formed during slow cooling from the melt. The sample preparation was made with modulated cooling using a cool-heat mode. Re-heating the samples prepared by slow conventional and modulated coolings indicated that the melting point of the samples prepared by modulated cooling is considerably higher than the melting point of the samples crystallized with conventional cooling. Thus, the perfection of crystallites can be improved if the outer layers just deposited on their surface are re-melted and re-crystallized immediately.

Restricted access

Abstract  

Thermal characterization is proposed as analytical methodology for the purity assay of lapachol, and for determination of the quality parameters of capsules containing this molecule. The TG data revealed that lapachol is more stable in the presence of adjuvants, showing the good quality of the formulation. The kinetic parameters obtained were lower for lapachol drug than for the formulated lapachol. The DSC data demonstrated good compatibility between lapachol drug and the adjuvant in the formulated lapachol, and did not reveal impurities such as secondary products of the isolation and recrystallization processes. The data were confirmed by the DSC-photovisual findings.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: P. Espeau, B. Nicolaï, R. Céolin, M. Perrin, L. Zaske, J. Giovannini, and F. Leveiller

Abstract  

Investigation into the thermal behavior of orthorhombic Forms I and II of spironolactone, by means of differential scanning calorimetry and high-resolution X-ray powder diffraction, showed that Form I melts then recrystallizes into Form II at 373–393 K, i.e. in the temperature range within which high resolution X-ray powder diffration showed that Form I transforms into Form II. Refinements of the lattice parameters of the two forms indicated that Form I is denser than Form II in the range from 298 K up to the temperature at which it melts.

Restricted access

Abstract  

The systematics of isotopic exchange in a heterogeneous batch system between a dilute aqueous solution and an adsorbate or the solid adsorbent are discussed. In particular, the influence of the experimental precision on the detection of an eventual non-reactive fraction of the adsorbate is considered, down to ~ 5% of which is detectable. The exchange with the solid adsorbent is illustrated by the case of45Ca2+ and calcite. The minimum layer thickness observable in surface exchange is ~ 0.05 m. The same formalism can be applied to uptake due to recrystallization of the solid. It enables distinction between this phenomenon and diffusion into the solid.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: M. Matthews, I. Atkinson, Lubaina Presswala, O. Najjar, Nadine Gerhardstein, R. Wei, Elizabeth Rye, and A. Riga

Abstract  

Dielectric analysis (DEA), supported by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), powder X-ray diffraction analysis (PXRD) and photomicrography, reveal the chiral difference in the amino acids. The acids are classified as dielectric materials based on their structure, relating chirality to the vector sum of the average dipole moment, composed of the constant optical (electronic) and infra-red (atomic) polarizabilities, as well as dipole orientation. This study encompasses 14 L-and D-amino acid isomers. Physical properties recorded include AC electrical conductivity, charge transfer complexes, melting, recrystallization, amorphous and crystalline phases, and relaxation spectra, activation energies and polarization times for the electrical charging process.

Restricted access

Abstract  

Isomorphic substitution, accompanied by surface adsorption, of a trace cation into a crystalline host matrix from its saturated solution can be studied by a double radiotracer experiment. Recrystallization of the matrix and uptake of the trace cation are thus measured simultaneously. This paper gives the formulation of the radiotracer experiment and the precision with which mole fractions of the trace cation in both phases, may be derived from it. The final result is thus a set of coexisting mole fractions and their uncertainties as a function of time. As an illustration, the case of calcite as the host matrix and CdII as the trace cation is considered.

Restricted access

Abstract  

Differential scanning calorimetry (DSC) was used to construct phase diagrams of binary mixtures of alkylcyclohexanes and to characterize metastable phases formed in the binary mixtures. The experimentally measured liquidus curves were compared to the liquidus curves calculated using ideal solution theory. The measured phase diagrams of pentadecylcyclohexane/nonadecylcyclohexane and octadecylcyclohexane/nonadecylcyclohexane binary mixtures are consistent with theoretical phase diagrams constructed based on the assumption that these mixtures form eutectic systems. It was also observed that a metastable phase formed in some binary mixtures of pentadecylcyclohexane/nonadecylcyclohexane under fast cooling conditions. It is hypothesized that this metastable phase recrystallizes into the eutectic phase upon heating.

Restricted access