Principle of determining nitrite content
After diazotization with p-aminobenzene sulfonic acid under the condition of hydrochloric acid acid, nitrite combines with N-1-naphthylethylenediamine hydrochloride to form a rose-red dye, which is visually compared with a standard color solution of a known concentration, and the amount of nitrite in the kimchi is estimated.
Determination of nitrite content
(1) The solutions to be prepared are:
p-aminobenzenesulfonic acid solution, N-1-naphthylethylenediamine hydrochloride solution, sodium nitrite solution, extractants (cadmium chloride and barium chloride), aluminum hydroxide emulsion and sodium hydroxide solution.
(2) The basic steps for the preparation of the standard color solution are:
① Use a graduated pipette to aspirate a volume of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5mL of sodium nitrite solution was placed in the cuvette, and the other cuvette was taken as a blank control.
②Add 2.0mL of p-aminobenzenesulfonic acid solution to each tube and mix well for 3~5 minutes.
③ Add 1.0mL of N-1-naphthylethylenediamine hydrochloride solution to each tube.
4) Finally, the solution was diluted to 50mL with distilled water.
(3) The steps for preparing the sample treatment solution are:
① Weigh 0.4 kg of kimchi, crush and squeeze the juice, and filter the juice to obtain about 200mL.
②Take 100mL of juice poured into a 500mL volumetric flask, add 200mL of distilled water and 100mL extractant, shaking the bed shaking for 1h, and then add 40mL of sodium hydroxide solution, and finally with distilled water to 500mL and immediately filtered to obtain the filtrate.
3, 60mL of filtrate was transferred to a 100mL volumetric flask, and the filtrate was fixed with aluminum hydroxide emulsion and then filtered to obtain a colorless and transparent filtrate.
(4) The steps for colorimetry are:
① Transfer 40mL of filtrate into a 50mL colorimetric tube and number it.
②Add 2.0mL of p-aminobenzenesulfonic acid solution and 1.0mL of N-1-naphthylethylenediamine hydrochloride solution in turn and volume to 50mL, mix well and let stand for 15min.
③Observe the change of color and compare with the standard color solution to record the nitrite content.
④Calculate the nitrite content in the sample filtrate (40mL).