Principle and precautions for the determination of nitrite and nitrate in food by spectrophotometry - Master's thesis - Dissertation

Principle and Precautions for Determination of Nitrite and Nitrate Content in Food by Spectrophotometry

Key words: spectrophotometer; nitrite; analysis instrument ; (a) determination of nitrite and nitrate content in food - spectrophotometry principle after precipitation of protein, fat removal, After diazotization of nitrite and p-aminobenzenesulfonic acid under weak acid conditions, coupling with naphthalene diamine hydrochloride forms a purple-red dye, which is quantitatively compared with the standard to determine the content of nitrite. The nitrate is reduced to nitrite by a cadmium column, and the total amount of nitrite is measured, and the content of the nitrate is obtained by subtracting the content of the nitrite from the total amount. The detection limits of nitrite and nitrate in this method were 1 mg/kg and 1.4 mg/kg, respectively. This method is extracted from GB/T 5009.33—2008 and is applicable to the determination of nitrite and nitrate in food. (2) Precautions 1 Cadmium is a harmful element. When making sponge cadmium or cadmium column, do not touch it directly by hand, and be careful not to get it on the skin. Rinse immediately with water if contacted. The cadmium-containing waste liquid in the preparation and treatment process should be discharged after treatment to avoid environmental pollution. 2 It is best to carry out in the water when preparing sponge cadmium and filling cadmium column. The cadmium particles are easily oxidized when exposed to air. After each use of the cadmium column, it should be washed with 25mL of 0.1mol/L hydrochloric acid, then twice with double distilled water, 25mL each time, and finally covered with water with cadmium column. 3 The preparation of spongy cadmium must be carried out in strict accordance with the prescribed method to ensure its reduction effect. When the sample is continuously tested, it is not necessary to wash the cadmium particles every time. If it is not used within a few hours, the cadmium particles must be washed as described above. In order to ensure the accuracy of the nitrate determination results, the reduction efficiency of the cadmium column should be checked and determined frequently. The cadmium column was properly maintained and there was no significant change in efficiency after one year of use. 4 When precipitating protein, the amount of zinc sulfate should not be too much. Otherwise, when it is reduced by cadmium column, Zn(OH)2 precipitates due to the addition of ammonia buffer with pH value of 9.6-9.7. Cadmium column, influence measurement. In addition to controlling the pH value of the solution, the ammonia buffer solution can alleviate the reduction of cadmium to nitrite, and can also act as a complexing agent to prevent precipitation of Cd2+ and OH- formed by the reaction. Key words: spectrophotometer; nitrite; mass spectrometer ; UV-1100 ultraviolet spectrophotometer; UV-1200 ultraviolet spectrophotometer