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  • Author or Editor: M. Wesołowski x
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The quality assessment of commercial soybean oils was evaluated on the basis of chemical and thermal analyses. The most substantial chemical parameters, viz. the density, refractive index and saponification, iodine and acid numbers were estimated. The thermal parameters were determined on the grounds of the TG and DTG curves. There are temperatures for the onset, end and successive mass losses. To find the relation between the chemical and thermal parameters, regression and principal component analyses were applied. The results of principal component analysis indicate that the TG and DTG techniques are at least in equal degree useful in defining the quality of soybean oils, as compared with the chemical analyses.

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A short survey is given of some aspects of the application of thermoanalytical methods, especially differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetry (TG), in solid-dosage technology. The usefulness of these methods in the prediction of drug-excipient compatibility, studies of solid-dispersion systems, the analysis of enantiomers and racemates, measurement of the time of tablet disintegration, the analysis of drug formulations and studies of the processes of grinding and drying of drugs is discussed.

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Abstract  

The suitability of the derivative thermogravimetric and principal component analyses for the assessment of service performance of lubricating oils has been studied. A total sum of 179 samples has been examined, including M-20 Bp, MS-20 p, Marinol CB SAE-30 and DS-11 oils. The results indicate that principal component analysis greatly assisted in the analysis of the quality of lubricating oils by derivative thermogravimetric technique. Considering that, this multivariate statistical method can be applied to the differentiation of oil samples taking into account degree of their degradation in the oil system of an engine.

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Abstract  

The thermal decomposition of benzoic acid and its derivatives containing —OH, —NH2, —COOH and —SO3H functional groups as substituents in ortho, meta and (or) para position together with sulphanilic acid was investigated. The analyses were performed using derivatograph, sample mass ranged from 50 to 200 mg, heating rates from 3 to 15 K min−1 and static air atmosphere. It has been established that thermal decomposition of these aromatic acids proceeds through three common stages. In the first stage the phase transformations occur. The following two stages are due to the formation of intermediate products of the thermal decomposition and their combustion. Principal component analysis (PCA) was applied for evaluation of the results. Thanks to this method the influence of specific functional groups and their positions on the benzene ring on the thermal decomposition of the compounds under investigation was determined.

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Thermal decomposition of methylxanthines

Interpretation of the results by PCA

Journal of Thermal Analysis and Calorimetry
Authors: M. Wesolowski and P. Szynkaruk

Abstract  

The thermal decomposition of theophylline, theobromine, caffeine, diprophylline and aminophylline were evaluated by calorimetrical, thermoanalytical and computational methods. Calorimetrical studies have been performed with aid of a heat flux Mettler Toledo DSC system. 10 mg samples were encapsulated in a 40 μL flat-bottomed aluminium pans. Measurements in the temperature range form 20 to 400°C were carried out at a heating rate of 10 and 20°C min−1 under an air stream. It has been established that the values of melting points, heat of transitions and enthalpy for methylxanthines under study varied with the increasing of heating rate. Thermoanalytical studies have been followed by using of a derivatograph. 50, 100 and 200 mg samples of the studied compounds were heated in a static air atmosphere at a heating rate of 3, 5, 10 and 15°C min−1 up to the final temperature of 800°C. By DTA, TG and DTG methods the influence of heating rate and sample size on thermal destruction of the studied methylxanthines has been determined. For chemometric evaluation of thermoanalytical results the principal component analysis (PCA) was applied. This method revealed that first of all the heating rate influences on the results of thermal decomposition. The most advantageous results can be obtained taking into account sample masses and heating rates located in the central part of the two-dimensional PCA graph. As a result, similar data could be obtained for 100 mg samples heated at 10°C·min−1 and for 200 mg samples heated at 5°C min−1.

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The mechanism of thermal decomposition of binary and ternary systems containing salicylic acid, sodium salicylate and disodium salicylate sesquihydrate, sodium carbonate and sodium hydrogen carbonate were studied by means of thermogravimetric and differential thermal analysis. The possibility was demonstrated of analyzing ternary systems containing three unreactive or three reactive components. The results can be useful for monitoring the course of the commercial-scale manufacture of sodium salicylate and for checking declared compositions of salicylate mixtures.

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The suitability of the differential thermal and thermogravimetric techniques for the determination of compositions of solid and soft drug formulations has been studied. A total of 117 pharmaceutical preparations have been examined, including powders, dusting powders, capsules, granulates, tablets, tablets for sucking, effervescent tablets, dragees, suppositories and ointments. Both techniques have been shown to be applicable for identification of pharmaceutical preparations. A specification has been made of thermal processes which can be employed for assaying the main components of the preparations. A rough estimate of the relative errors has been given.

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Abstract  

The studies on the concentration of total nitrogen, phosphorus, sulphur, chlorine, iodine and boron as well as on the thermal decomposition of commercial raw plant materials used in medicine were performed. The 50 independent samples of herbs originating from 25 medicinal plant species collected in 1986–92 were analysed. The content of non-metallic elements was determined spectrophotometrically after previous mineralization of plant sample. The thermal decomposition was performed using the derivatograph with the application of 100 mg samples and heating rate of 5C min−1. In order to obtain more clear classification of the analysed plant materials principal component analysis (PCA) was applied. Interpretation of PCA results for two databases (non-metals and thermoanalytical data sets) allows to state, that samples of herbs from the same plant species in majority of cases are characterized by similar elemental composition and similar course of their thermal decomposition. In this way the differences in general chemical composition of medicinal plants raw materials can be determined.

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Abstract  

The quality of commercial vegetable oils is usually evaluated via chemical parameters such as density, refractive index, saponification, iodine and acid values. In this paper, the applicability of thermal parameters for the quality assessment of vegetable oils is proposed. In order to achieve this goal, different back-propagation neural network architectures were trained, using chemical and thermal parameters as inputs. To avoid any accidental correlation due to the random initialization of the weights, each topology was repeated three times and three networks were chosen, with 5-3-2, 8-5-2 and 13-6-2 structures. The error function sum square error (SSE) was used as the criterion for finalization of the learning process. A model was developed for the correct classification of oils with regard to their type and quality.

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