Determination of Total Nitrogen in Tobacco by Coulometric Titration
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.
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