Determination of Total Nitrogen in Tobacco by Selenium Powder Catalysis-Continuous Flow Analysis

About 0.2 g of the tobacco powder sample was taken into digestive tube, then 3 mL of mixed digestion reserve solution of selenium powder and sulfuric acid at mole ratio of 0.25% was added. After blending, 3.0 mL of 30%(mass fraction) hydrogen peroxide was added. The mixture was heated to 330 ℃, keeping for 1.0 h. After cooling, the obtained solution was made its volume up to 75 mL by distilled water. Total nitrogen was determined by continuous flow analyzer at 600 nm. As shown by the results, linear relationship between the corresponding absorbance and mass concentration of total nitrogen was found in the range of 0.020 5-0.205 0 g·L^-1, with detection limit (3s) of 2.364 mg·L^-1. This method was applied for determination of laboratory control samples, and the determined values were consistent with the nominal values. Laboratory control sample was determined 6 times in parallel for intraday and 5 timies for interday by this method, with RSDs of the determined values less than 3.0%. Test for recovery was made by standard addition method, giving results in the range of 95.1%-102%.