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Thermometry, Enthalpimetry

Thermometric and enthalpimetric analysis

Journal of Thermal Analysis and Calorimetry
Author:
L. S. Bark
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The determination of isonicotinic acid hydrazide in the dosage form of isoniazid tablets is done using thermometric titrimetry. The hydrazide is oxidized by hexacyanoferrate(III) ions. It is not necessary to separate the active ingredients from the powdered sample. The results from the proposed method are compared with those obtained using the standard B.P. method.

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The oxidizing power of hexacyanoferrate(III) in alkaline conditions is wellknown. Unfortunately many if its oxidation reactions are too slow at room temperatures for direct titrimetric procedures.

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A method is descubed for the determination of lead alkyl additives in gasoline by direct injection enthalpimetry. The method is a single step process, iodine monochloride solution is injected into a sample of the gasoline diluted with an equal volume ofo-xylene. The system can be arranged to gave a direct reading of the concentration of the permitted lead alkyls for several concentration ranges. Once calibrated the proposed method can be operated by semi-skilled workers. The precision and accuracy are within industrial limits. The main advantages of the method are those of low cost and low time of analysis.

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Some azo dyes have been assayed using D. I. E. The analysis is completed in less than 1 minute with an average error of 1.05% at the 1 mMole level.The reagent used is titanium(III)chloride. Degassing of the solutions is not necessary.

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An enthalpimetric method for the rapid, low cost assay of reducing sugars in soft drinks is reported.

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A simple, rapid and accurate direct injection enthalpimetric (DIE) method has been developed for the determination of the iodine value of some commercial edible oils. A significant heat pulse of halogen addition reaction of the double bonds of unsaturated fatty acid esters in the oils is produced by injecting a solution of iodine monochloride into the sample solutions. The method is calibrated against real samples and the standard compounds (oleic, linoleic and linolenic acids) whose iodine values have been determined by a standard method. Once calibrated, the proposed method can be operated routinely by semi-skilled personnel. The method is sensitive and give results as acceptable as those obtained by standard methods. The main advantages of the method are those of time and cost of analysis and the potential of the enthalpimetric method for automation.

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A rapid and accurate direct injection enthalpimetric (DIE) method has been developed for the determination of the water content in some oils and fats of commercial interest. The method combines the DIE and the Karl Fischer Reagent procedures and is calibrated against real samples whose water content have been determined by a standard distillation method using toluene as the immiscible solvent. The reproducibility and precision are equivalent to those of the standard method for the water content of materials such as soya bean oil. The procedure is able to determine water contents in compounds such as lard, which cannot be determined by the Dean & Stark method. Once calibrated, the proposed method can be operated routinely by semi-skilled personnel. The main advantages of the method are those of time and the cost of analysis.

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A series of mixtures, each containing at least two of the ions phosphate, arsenate(V) and arsenate(III) have been determined enthalpimetrically using the concept of the additivity of partial molar heat pulses. The non-selective reactions used involved precipitation and redox reactions. The accuracy at the 1mM level is within 1.5%, and the total time of a determination of a mixture of all three anions is less than 10 minutes after preparation of the sample solution, which is prepared for insoluble phosphates, by metathesis with sodium carbonate.

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