Purity thermal methods

The thermal method is based on the much higher solubiUty of KCl in hot water as compared to the solubiUty of NaCl. The KCl is recovered in vacuum crystallizers, filtered or centrifuged, dried, and sometimes granulated by compaction. Product from the thermal beneficiation method usually is of relatively high purity and is particularly suitable for use in formulating solution-type fertilizers. Guaranteed K2O content of this product is usually 62%... 

The sample temperature is increased in a linear fashion, while the property in question is evaluated on a continuous basis. These methods are used to characterize compound purity, polymorphism, solvation, degradation, and excipient compatibility [41], Thermal analysis methods are normally used to monitor endothermic processes (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, and chemical degradation) as well as exothermic processes (crystallization and oxidative decomposition). Thermal methods can be extremely useful in preformulation studies, since the carefully planned studies can be used to indicate the existence of possible drug-excipient interactions in a prototype formulation [7]. 

R. L. Blaine and C. K. Schoff, Purity Determinations by Thermal Methods, ASTM Press, Philadelphia, 1984. 

Thermal methods have found extensive use in the past as part of a program of preformulation studies, since carefully planned work can be used to indicate the existence of possible drug-excipient interactions in a prototype formulation [2], It should be noted, however, that the use of differential scanning calorimetry (DSC) for such work is less in vogue than it used to be. Nevertheless, in appropriately designed applications, thermal methods of analysis can be used to evaluate compound purity,... 

A very comprehensive treatment of thermal methods for determining purity has been given by Wendlandt, but not much of it is of direct relevance to the matters discussed here (Wendlandt, 1986). 

DSC finds many applications in characterizing materials. Quantitative applications include the determination of heals of fusion and the extent of crystallization for crystalline materials. Glass transition temperatures and melting points arc useful for qualitative classification of materials, although thermal methods cannot be used alone for identification. Melting points are also very useful in establishing the purity of various preparations. Hence, Ihcrmal methods are often used in quality control applications. 

S. A Morus, in "Purity Dcicrminaiions hy Thermal Methods". (Eds R L, Blaine iiod C.K. Seboff). ASTM S]X ia) Tovhnicul Publication 838, Ameitcan Sociely forTcMing and Materials. Philadelphia, 1984, p.22. 

J.P. Eldef. tn Purity Deieiniinuloih by Thermal Methods", (E3ck R.I.. Blaine and C.K SebofT). ASTM Special Technical Publication 838, American Sociely for Testing and MateriaK. PfeiLtdelpbia, 1984, p.S0,... 

A.R. MeOhie. in "Purity Deicrminotions by Thermal Methods", i Eds R.L. Blaine and C.K. SchofO. ASTM Special Technicnl Publicaiion 8.38, American Sociely for Tesliitg and Materials. Philadelphia, 1984, p,6l. 

R.L. Blaine and C.K. SchofftEds). Purity Dcteraiinatioiui b) Thermal. Methods,... 

With respect to organic compounds, those that are precursors to pharmaceuticals have attracted increasing interest from the viewpoint of their thermal properties, and TA techniques are used frequently in quality control procedures for such compounds. A wide variety of common and less common pharmaceuticals have also been investigated using a variety of thermal methods - mainly BSC and mainly in the context of purity determination. There is also potential for using TA techniques to identify pharmaceutical activity and for shelf-life determinations. 

Differential scanning calorimetry (DSC) directly measures the heat flow to a sample as a function of temperature. A sample of the material weighing 5 to 10 g (18-36 oz.) is placed on a sample pan and heated in a time- and temperature-controlled manner. The temperature usually is increased linearly at a predetermined rate. The DSC method is used to determine specific heats (see Fig. 9-4), glass transition temperatures (see Fig 9-5), melting points (see Fig. 9-6), and melting profiles, percent crystallinity, degree of cure, purity, thermal properties of heat-seal packaging and hot-melt adhesives, effectiveness of plasticizers, effects of additives and fillers (see Fig. 9-7), and thermal history. 

There is a growing awareness that electrochemical methods of synthesis may be used to achieve controUed purity compounds which are difficult to produce by chemical or thermal methods. A general strategy for the synthesis of metal salts or complexes is controlled anodic dissolution of the pure metal in a suitable electrolyte. In a simple case, the anode process may be the formation of a soluble, hydrated metal ion (as in electro refining, section 4,3) ... 

Alloy catalysts are prepared either by co-precipitation with Pt or by sequential deposition. One widely used method is sequential deposition of alloying elements by carbo thermal process on Pt loaded carbon support. However, carbo thermal method is suitable for non-noble metals and does not yield high purity alloys. This is due to the presence of large quantity of unalloyed metal and the need to be Cleaned by soaking in acid. The other method involves formation of various types of complexes of Pt and the alloy metal to form a mixed colloid Sol . This mixed colloid when adsorbed on the carbon support yields highly uniform alloy distribution. 

Thermal analysis gives information on the fundamental behavior and structure of materials based on their thermochemical and thermophysical properties. Differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetry (TG), dilatometry, and other related dynamic thermal methods serve as analytical tools for characterizing a wide variety of solid materials. Information obtainable by these methods includes phase relationships, identification and measurement of impurities in high-purity materials, fingerprint identifications, thermal histories of the material, and dissociation pressures. 

Brennan WP, Divito MP, Ryans RL, et al. Purity determinations by thermal methods. In Blaine, Schoff (eds.), Purity Determinations by Thermal Methods ASTM Special Technical Publication 838. ASTM STP 838. 1984 5-15. 

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