Determination of volatile basic nitrogen (TVB nitrogen)
1. determination method of semi-trace nitrogen
Principle (1): protein is decomposed by enzymes and bacteria to produce alkaline nitrogen-containing substances, including ammonia, primary amine and secondary amine. These substances are volatile and can be distilled in alkaline solution, titrated with standard acid and calculated.
(2) reagents
① magnesium oxide suspension ②2% boric acid solution (absorption solution) ③0.2% methyl red ethanol solution ④0. 1% methylene blue aqueous solution.
When in use, ③ and ④ are mixed into mixed indicator ⑤0.0 100N hydrochloric acid standard solution or 0.0 100N sulfuric acid standard solution.
(3) Instruments
① Semi-micro nitrogen determinator: Markhan type ② Micro burette: minimum scale 0.0 1ml.
(4) Operation method
① Preparation of sample solution: After removing the fat, bones and tendons from the sample, chop it up and stir it evenly, weigh 10g into the conical flask, add 100ml of water, shake it from time to time, soak it for 30min, then filter it, and put the filtrate in the refrigerator for later use.
② Determination: Put the conical flask containing 10ml absorption liquid and 5-6 drops of mixed indicator liquid at the lower end of the condensing tube in advance, insert the liquid level absorbed by the conical flask at the lower end, accurately suck 5ml of the above sample filtrate into the reaction chamber of the distiller, add 5ml 1% magnesium oxide suspension, plug it quickly, add water to prevent air leakage, and introduce steam. When the steam in the still is full, close the steam outlet pipe. Starting from the first drop of condensate in the cold parallel pipe, stop the distillation after 5 minutes, and titrate the absorption solution with 0.0 100N hydrochloric acid standard solution or 0.0 100N sulfuric acid standard solution, and the end point is blue purple. At the same time, do reagent blank test.
(5) Calculation
(V 1-V2)×N 1× 14
X 1= - × 100
m 1×5/ 100
Where: x1-the content of volatile basic nitrogen in the sample, mg/ 100g.
V1-the volume of hydrochloric acid or sulfuric acid standard solution consumed by the sample solution for determination, ml.
V2—— the volume of hydrochloric acid or sulfuric acid standard solution consumed by reagent blank, ml.
Molar concentration of standard solution of n 1- hydrochloric acid or sulfuric acid, mol/L
M 1- sample mass, g
14—— 1N standard solution of hydrochloric acid or sulfuric acid 1ml is equivalent to milligrams of nitrogen.
2. Microdiffusion method
Principle (1): Volatile nitrogen-containing substances are released in alkaline solution, volatilized in diffusion dish at 37℃, absorbed in absorption solution, titrated with standard acid, and the content is calculated.
(2) reagents
① Saturated potassium carbonate solution: weigh 50g of potassium carbonate, add 50ml of water, slightly heat to help dissolve, and take the supernatant when using.
② Water-soluble gum: Weigh 10g Arabic gum, add 10ml water, 5ml glycerol and 5g anhydrous potassium carbonate (or anhydrous sodium carbonate) and grind evenly.
③ Absorption solution: mixed indicator solution, 0.0 100N hydrochloric acid or sulfuric acid standard solution, the same as semi-trace nitrogen determination method.
(3) Instruments
① Diffusion plate (standard type): glass, with the total diameter of the inner and outer cavities of 665,438+0 mm and the diameter of 35mm in the inner chamber; External chamber depth 10mm, internal chamber depth 5 mm; The outer chamber wall is 3mm, the inner chamber wall is 2.5mm, and the back wall is thick with a glass cover, as shown in figure 1- 1. Other models can also be used.
② Micro burette: The minimum scale is 0.0 1ml.