应用响应曲面法优化凯氏定氮法的消解条件

Optimization of Digestion Conditions in the Kjeldahl Method for Nitrogen Analysis Using Response Surface Methodology

经典凯氏定氮法是通过观察消解反应现象来控制温度和时间,对于数量较多的样品同时消解会耗费大量的人力及时间,因此需要采用合理的试验设计方法确定最佳消解温度和时间,以实现批量消解样品,提高分析效率。本文利用响应曲面法对凯氏定氮法中的消解条件进行了优化分析,选择料液比、消解温度和消解时间作为优化因素,研究三因素的不同水平对氮含量测定的影响。通过响应曲面分析得到最优的消解条件为:料液比(g/mL)=0.3∶5,消解温度260℃,消解时间60 min。重复实验结果表明,样品在优化的条件下能够很好地消解,重现性较好;标准物质的氮含量的实验测定值(1310×10-6)与标准值(1300×10-6)基本一致,两者的对数误差绝对值为0.003,方法的准确性高。应用响应曲面试验设计方法,对于评价凯氏定氮法中三个消解条件对氮含量的非线性影响起到了很好的优选作用,能更好地预测实验因素对分析结果的影响趋势,可以准确控制消解温度和消解时间,对于提高分析效率具有实用意义。

Reaction phenomenon has always been observed time in classical Kjeldahl method for nitrogen analysis, but to control digestion conditions such as temperature and it is not suitable for a large number of samples which need a lot of manual labour and time. Therefore it is necessary to optimize digestion conditions for simultaneous digestion of a large number of samples in order to increase efficiency. In this experiment, response surface methodology （RSM） was applied for the optimization of digestion conditions in the Kjeldahl method for nitrogen analysis. In RSM analysis, solid/liquid ratio, digestion temperature and digestion time which affect the determination of nitrogen content were examined. Results show that the optimal parameters were determined as follows： solid/liquid ratio of 0. 3 ： 5 （g/mL）, digestion temperature of 260℃, and digestion time of 60 min. Under the optimized conditions, the calculated value （ 1310 × 10-6） and certified value （ 1300× 10 -6） of nitrogen content are basically consistent with the absolute value of logarithmic error of 0. 003 giving it practical significance. The BBD experiment of digestion condition in Kjeldahl method plays a very good role in optimizing the nonlinear effects of measuring nitrogen content, which can better predict the trend of the impact of experimental factors on the results. The research provided the scientific basis and theory guidance for optimization research of digestion conditions by correctly using RSM. It will speed up analysis and also save time by adjusting the digestion temperature and digestion time accurately.