Search Results

You are looking at 1 - 10 of 32 items for :

  • "combined techniques" x
  • All content x
Clear All

Abstract  

Modern thermal analysis, microcalorimetry and new emerging combined techniques which deliver calorimetric, microscopic and spectroscopic data offer a powerful analytical battery for the study of pharmaceuticals. These techniques are very useful in all steps of development of new drug products as well as methods for quality control in production. The characterization of raw materials enables to understand the relationships between polymorphs, solvates and hydrates and to choose the proper development of new drug products with very small amount of material in a very short time. Information on stability, purity is valuable for new entities as well as for marketed drug substances from different suppliers. Excipients which vary from single organic or inorganic entity to complexes matrixes or polymers need to be characterized and properly controlled. The thermodynamic phase-diagrams are the basis of the studies of drug-excipients interactions. They are very useful for the development of new delivery systems. A great number of new formulations need proper knowledge of the behaviour of the glass transition temperature of the components. Semi-liquid systems, interactions in aqueous media are also successfully studied by these techniques.

Restricted access

Abstract  

A NAA-PIXE combined analysis has been applied to the precise measurement of the concentrations of Nb and Ti in Nb–Ti alloy ingot. The ingot is used in the production of superconductors and the concentration should be controlled very strictly. The ingot cross section could be analyzed with an accuracy of better than 1% by the use of NAA for the preparation of standard samples and PIXE for the nondestructive rapid scan of the surface. The radial and azimuthal concentration profiles of the ingot could be obtained.

Restricted access

Summary Thermoanalytical techniques (TG, DSC) are frequently used in the investigation of the thermal properties of cyclodextrins and their inclusion complexes. However, the above techniques do not provide information on the chemical composition of the evolved fragments upon the thermal decomposition. In this study &-, &- and &-cyclodextrins and 4 methylated and 3 ethylated &-CD derivatives were investigated with a TG-MS combined thermoanalytical technique in order to get information about their fragmentation behaviour. By comparison of the TG/DTA curves, a different thermal behaviour was found for each of the native and the chemically modified cyclodextrins. Except for the water loss profiles and the solid-solid phase transformations, the thermal behaviour of the (investigated) native CDs do not show remarkable differences. However, the chemical modification of the native &-CD resulting in a new compound may change the strength of interactions between host and guest causing differences in the thermal stabilities of the derivatives. The mass spectrometry results supported the observed thermal differences and showed significant alterations in the fragmentation of ethylated and methylated compounds. The investigated natural CDs possess a very similar fragmentation profile, due to the common &-D-glucopyranose building units. In the case of modified CDs characteristic signals of the substituents are present.

Restricted access

Abstract  

The polymorphic behaviour of the purine derivative MKS 492 was studied with investigations of suspensions of selected samples in different solvents and of samples obtained by crystallizations. The samples were analyzed by DSC, TG and X-ray diffraction. Six different crystalline modifications called A, B, B, C, D and E and an amorphous form were identified. Four pure crystalline modifications, A, B, C and D have been manufactured and characterized by DSC, X-ray, IR, solubilities, densities, hygroscopicity and dissolution measurements. The four forms A, C, D and E are monotrop to the form B. The form B is enantiotrop to the form B, which revealed the highest melting point of all known polymorphs. This form B is only stable at high temperature. Temperature resolved X-ray diffraction was very helpful for proper interpretation of the thermal events. The melting peaks of the forms A and C and the endothermic peak corresponding to the enantiotropic transition B into B occur in a narrow range of temperature. The form B which is the most stable one at room temperature has been chosen for further development. Quantitative methods to determine the content of the forms A, C and D in samples of form B or to determine the content of form A, B and D in form C have been developed by using X-ray diffraction. Limits of detection are 1 or 2%. For the quantitative determination of the amorphous fraction, X-ray diffraction and microcalorimetry are compared. For high amounts of the amorphous fraction, the X-ray diffraction method is preferred because it is faster. Microcalorimetry is very attractive for levels below 10% amorphous content. The lowest limit of detection is obtained by microcalorimetry, about 1%.

Restricted access

Abstract  

Scanning transitiometry combines three state variables (P,V,T) with a heat effect measured in strictly defined thermodynamic conditions. By slowly scanning one of the state variables when the other one is kept constant, the transitiometer permits to determine simultaneously two thermodynamic derivatives, always one is thermal and the other one mechanical. This study presents a number of applications of scanning transitiometry in various fields (dense liquids, supercritical systems, polymers, food systems) and presents results, often impossible to obtain with other known techniques.

Restricted access

Abstract  

Four amino acids and four different hair samples were studied in order to get information about the decomposition of human hair, using combined (TG-MS) and DSC techniques. The thermal stability of the investigated amino acid samples was different. Since they contain identical functional groups (-NH2, -COOH) some common mass/charge units were identified. However, due to their different chemical composition remarkable differences have also been obtained. The results of the investigation of the amino acids were helpful to study the thermal fragmentation of the hair samples. In our experiments, the effect of the heating rates was also studied.

Restricted access

Abstract  

The combined technique TGA/DTA/MS, thermogravimetric analysis/differential thermal analysis/mass spectrometry, has been used, in conjunction with other analytical techniques, FTIR, SEM, XRD, and optical microscopy, to analyze a specific patching material that had become seriously discolored on its surface after being used to repair a historic stone pillar at Bethesda Terrace in Central Park, New York in the 1980s. The stone patch was found to contain a polyacrylate binder which was associated with the discoloration.

Restricted access

Abstract  

This paper discusses the possibility to represent scientific development by second-order networks in different modalities. In particular, a specific modality structured by subfield-to-subfield relations is presented. By constructing such co-subfield maps for successive periods of time, we were able to describe the changing subfield relations within the field of chemical engineering. In this way, dynamical processes in the development of a field as a whole can be revealed. Advantages and disavantages as compared to co-citation and co-word mapping techniques are discussed and the importance of developing combined techniques is stressed.

Restricted access

Abstract  

The chemical-physical decomposition processes that occur in a brake pad heated to 1000C have been studied. This temperature can be reached when a brake pad is applied. Thermogravimetry and differential thermal analysis were used in combination with evolved gas analysis, and image analysis using a scanning electron microscope. A brake pad is essentially a mixture of iron, carbon and binder. Combined techniques have been used,because of chemical reaction overlap, to determine how and at what temperature the binder decomposes, the coal and graphite combust and the iron oxidises. This work enables the development of brake pads that are stable at high temperature.

Restricted access