库仑滴定法测定烟草中总氮的含量

Determination of Total Nitrogen in Tobacco by Coulometric Titration

取已处理过的烟草样品0.20 g,用0.2 g硫酸铜、0.3 g硫酸钾和6 mL硫酸于170℃消解1 h后,再升温至370℃继续消解2 h。待消解液冷却至室温后,滴加8 mol·L^(-1)氢氧化钾溶液,调节消解液pH至4.0~5.0,用水定容至50 mL。以铂电极-铂丝对电极作电解电极对,铂电极作指示电极对,四硼酸钠-溴化钾溶液(溴化钾浓度为1.2 mol·L^(-1),pH 8.6~8.9)作电解质溶液,在适当的电解电流下,滴定剂BrO~-定量滴定预处理后样品溶液中NH_4~+,通过到达滴定终点的电解时间,根据法拉第定律测定总氮的含量。结果表明,按标准加入法进行回收试验,回收率为95.1%~109%,测定值的相对标准偏差(n=5)均小于2.0%。方法用于实际样品的分析,与YC/T 161-2002中连续流动法测定结果相比较,结果无显著性差异,与杜马斯燃烧法的测定结果相近,但本方法无需提前准备大量试剂,且操作简便,耗时短。

The pretreated tabacoo sample(0.20 g)was digested in 0.2 g of copper sulfate,0.3 g of potassium sulphate and 6 mL of sulfuric acid at 170℃for 1 h,and then the mixture was heated to 370℃,which was continuously digested for 2 h.After cooling to room temperature,8 mol·L-1 KOH solution was added drop-wise to adjust pH of digestion solution to 4.0-5.0,and the mixture was made its volume up to 50 mL by water.In the condition of platinum electrode-platinum wire electrode as working electrode pairs,platinum electrodes as indicating electrode pairs,sodium tetraborate-potassium bromide solution(KBr concentration of 1.2 mol·L-1,pH 8.6-8.9)as electrolyte solution,with appropriate electrolysis current,the titrant BrO-quantificationally titrated NH4+in sample solution after pretreatment.Total nitrogen was determined by electrolysis time that reached to titration end-point according to Faraday's law.As shown by the results,test for recovery was made by the standard addition method,giving results in the range of 95.1%-109%,with RSDs of the determined values(n=5)less than 2.0%.This method was applied to the analysis of actual samples,and there was no significant difference between this method and continuous flow analysis method in YC/T 161-2002.The results obtained by this method were similar to those of the Dumas combustion method.However,this method did not require a large amount of reagents to be prepared in advance,and it was easy to operate with short time consumption.