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The influence of both light and heat on the stability of nitrofurazone aqueous solution was studied. Results show that in either heating experiments or the exposure to light at high temperatures, the degradation rate obeyed zero-order kinetics. The total rate constant ktotal caused by both light and heat can be divided into two parts: ktotal =kdark klight, where kdark and klight are the degradation rate constants caused by heat and light, respectively. The klight can be expressed as klight=Alight*exp(-Ea,light/RT)*E, where E is the illuminance of light, and Alight and Ea,light both are experimental constants. The values of these kinetic parameters were determined based on the experiments in the dark and upon exposure to three different light sources. Results show that the values of Alight and Ea, light varied with the light source. To save time, labor, and drugs, exponential heating experiments were employed and compared with the isothermal experiments. Results indicated that kinetic parameters obtained by exponential heating experiments are comparable to those obtained by isothermal experiments either in the dark or upon exposure to light. 相似文献
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抗氧剂亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠氧化反应速率常数的测定 总被引:2,自引:0,他引:2
为评价抗氧剂的抗氧化能力, 测定了抗氧剂亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠在水溶液中与氧反应的速率常数. 在溶液中连续通入足量的氧气, 维持溶解氧浓度恒定. 用碘量法测定亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠在水溶液中不同时刻的浓度, 用氧电极测定溶液中溶解氧的浓度, 作出亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠的降解曲线, 计算亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠氧化反应速率常数. 结果表明, 亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠在水溶液中与氧的反应均为零级反应. 由于在溶液中这三种抗氧剂存在解离平衡, 当溶液的pH值相同时这三种抗氧剂实质上是一样的, 其平均表观反应速率常数在25 ℃温度和pH 6.8, 4.0及9.2条件下分别为(1.34±0.03)×10-3, (1.20±0.02)×10-3和(6.58±0.02)×10-3 mol•L-1•h-1. 相似文献
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以维生素C及常用于其注射液中作稳定剂的焦亚硫酸钠为例, 测定了两组平行反应(维生素C无氧降解和有氧降解; 维生素C和焦亚硫酸钠的氧化反应)的动力学参数, 建立了维生素C的降解动力学方程. 结果表明维生素C无氧降解为零级反应; 在维生素C和焦亚硫酸钠的氧化反应中, 维生素C和焦亚硫酸钠的反应级数都为零, 溶解氧为一级; 维生素C溶液的吸光度变化在一定范围内和浓度降解量成线性关系. 根据建立的动力学方程, 从理论上计算得在维生素C溶液中加(或不加)焦亚硫酸钠时的贮存期分别为444 d(或152 d), 表明加入焦亚硫酸钠能显著延长维生素C溶液的贮存期. 相似文献
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