双氰胺熔点对照品熔点差异分析

目的: 探究中国药典和世界卫生组织双氰胺熔点对照品熔点差异的原因. 方法: 采用差示扫描量热分析(DSC)和热重/差热同步分析(TGA/SDTA)研究双氰胺熔点对照品的熔融过程,DSC升温速率10 ℃·min^-1,干燥气N₂流速50 mL·min^-1,TGA/SDTA升温速率20 ℃·min^-1,干燥气N₂流速25 mL·min^-1;并进一步通过HPLC法分析熔融前、中、后的样品. 结果: 差示扫描量热分析和热重/差热同步分析发现3个对照品的热力学行为基本一致,提示熔融后期可能已经热降解;HPLC法进一步证实双氰胺的熔融过程伴有部分降解. 结论: 热稳定性可能是造成中国药典和世界卫生组织双氰胺熔点对照品熔点差异的原因,双氰胺继续作为熔点对照品值得商榷.

Objective: To study the causes for difference of the melting point of dicyanodiamide reference substances(for melting point use)from Chinese pharmacopoeia (ChP) and the World Health Organization (WHO). Methods: The melting process of reference substances was explored by the method of differential scanning calorimetry (DSC) and thermogravimetric/differential thermal analysis (TGA/SDTA). In the experiments of DSC and TGA/SDTA, the heating rates were 10 ℃·min^-1 and 20 ℃·min^-1; and the gas flow rates of nitrogen were 50 mL·min^-1 and 25 mL·min^-1, respectively. In addition, samples before, during and after melting were analyzed by HPLC successively. Results: Refering to the methods of DSC and TGA/SDTA, the thermal behaviors were similar for three dicyanodiamide reference substances from ChP and WHO, indicating that degradation might occur at late stage of melting. By means of HPLC method, partial degradation was proved to exsit in the course of melting. Conclusion: Thermal stability may be the cause for difference of the melting point of dicyanodiamide reference substances from ChP and WHO, and the use of dicyanodiamide as the reference substance for melting point needs to be further studied.

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