全自动凯氏定氮仪测定牧草中粗蛋白含量的误差分析及应对措施

Error Analysis on Determination of Crude Protein in Herbage by the Automatic Kjeldahl Apparatus and Related Countermeasures

粗蛋白是评价牧草营养价值的重要指标,因此准确测定牧草中粗蛋白的含量尤为重要。常用凯氏定氮法测定牧草样品中的粗蛋白含量,但传统的凯氏定氮装置实验过程复杂且产生误差的来源比较多,相比之下,具有自动化程序的全自动凯氏定氮仪优势较为显著。本文通过用传统的凯式定氮法和全自动凯式定氮法分别对紫花苜蓿阿尔冈金、WL343HQ、劲能、金皇后、苜蓿王5个不同品种的干草样品中粗蛋白含量的测定,结果表明,全自动凯氏定氮仪法测定5份紫花苜蓿干草样品粗蛋白含量的RSD和SD均小于传统的凯氏定氮法,且回收率比传统的凯氏定氮法大。结论:采用全自动凯氏定氮法具有更高的精密度和准确度,更适用于测定牧草粗蛋白。同时,笔者从消化温度与时间、仪器管路和滴定系统的检查、空白值测定与准确率检验等三个方面对用全自动凯氏定氮法在测定中常见的误差因素进行分析并指出应对措施,为今后用全自动凯式定氮法得到高准确度的牧草粗蛋白测定值提供参考。

Crude protein is an important index for evaluating the nutritional value of herbage,so it is of great importance to determine the its content in herbage accurately.The Kjeldahl method is commonly used to determine the crude protein content,however,the traditional Kjeldahl apparatus has a complex experimental process and many sources of errors.In contrast,the advantages of automatic Kjeldahl apparatus,which has fully automatic procedures,are more obvious.In this paper,the crude protein content in five different varieties of hay samples consisting of Medicago sativa Linn,WL343HQ,Jinneng,Gold queen and Alfaking,were determined by both traditional and automatic Kjeldahl method.The results showed that the RSD and SD of crude protein content of 5 hay samples measured by the automatic method were both smaller than those measured by traditional method,and the recovery rate of the automatic method was larger than that of traditional method.In conclusion,the automatic Kjeldahl nitrogen determination method had higher precision and accuracy,and was more suitable for the determination of crude protein in herbage.At the same time,the common error factors in the determination by the automatic Kjeldahl method were analyzed from the three aspects of digestion temperature and time,inspection of the instrument pipeline and titration system,blank value determination and accuracy test,and the countermeasures were pointed out,some reference would be provided for the use of automatic Kjeldahl method in the future to obtain high-precision protein values.