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

Reaction phenomenon has always been observed to control digestion conditions such as temperature and time in classical Kjeldahl method for nitrogen analysis, but 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.