差示扫描量热法对味精中L-谷氨酸钠的分析

THERMOCHEMICAL ANALYSIS OF SODIUM L-GLUTAMATE IN GOURMET POWDER BY DIFFERENTIAL SCANNING CALORIMETRY (DSC)

采用差示扫描量热法(DSC)研究了一水谷氨酸钠的热分解过程,结果表明一水谷氨酸钠的热分解过程分为两个阶段,在155℃开始脱去结晶水,脱结晶水阶段动力学参数n=0.89,Ea1=152.8kJ·mol-1,A1=7.8×1018s-1,分子内脱水阶段动力学参数n=0.75,Ea2=274.4kJ·mol-1,A2=1.1×1030s-1,半寿命期为t1/2=1.3×109月。

The course of thermochemical decomposition of the sodium L-glutamate is studied by differential scanning calorimetry (DSC), and the results obtained show that the dehydration of sodium L-glutamate monhydrate proceeds in two stages. In the 1st stage, the crystal water is removed, starting at 155℃ and concluded at 186℃, as shown by peak(Ⅰ) in the DSC spectrum. The kinetic parameters obtained in this stage are as follows: n=0.89, E_(a1)=152.8kJ·mol^(-1) and A_1=7.8×10^(18)s^(-1). In the 2nd stage, in the range from 215～270℃, one molecule of H_2O is dehydrated from the L-glutamate molecule which undergoes a molecular rearrangement forming the pyro-glutamate (so-called pyrrolidonization). The following kinetic parameters are obtained in the 2nd stage∶n=0.75, E_(a2)=2744kJ·mol^(-1) and A_2=1.1×10^(30)s^(-1) IR-spectrometry is applied to characterize the thermochemical decomposition products.