S.L. 437.63 ст. 5to the flask an appropriate 1,2 g of copper of pumice time to time if then heat if the boiling overheated clear and sulfates. Allow to cool and Place in the quantity of 25 content. Add Connect the immerse the depth of at hydroxide observation Heat the 5.3 Titrate the solution (3.9) until the end 5.4

Procedure 5.1 Digestion

Weigh 1 g of the sample to the nearest 0,001 g and transfer the sample of the digestion apparatus. Add 15 g of potassium sulfate (3.1.), quantity of catalyst (3.2) (0,3 to 0,4 g of copper (II) oxide or 0,9 to

(II) sulfate pentahydrate), 25 ml of sulfuric acid (3.4) and a few granules stone (3.11) and mix. Heat the flask moderately at first, swirling from necessary until the mass has carbonized and the foam has disappeared[ more intensively until the liquid is boiling steadily. Heating is adequate acid condenses on the wall of the flask. Prevent the sides from becoming and organic particles from sticking to them. When the solution becomes light green continue to boil for another two hours, then leave to cool. 5.2 Distillation Add carefully enough water to ensure complete dissolution of the then add a few granules of zinc (3.3).

collecting flask of the distillation apparatus an exactly measures ml of sulfuric acid (3.5) or (3.6) depending on the presumed nitrogen a few drops of methyl red indicator (3.7). digestion flask to the condenser of the distillation apparatus and end of the condenser in the liquid contained in the collecting flask to a least 1 cm (see observation 8.3). Slowly pour 100 ml of sodium solution (3.8) into the digestion flask without loss of ammonia (see 8.1). flask until the ammonia has distilled over.

Titration excess sulfuric acid in the collecting flask with sodium hydroxide or (3.10) depending on the concentration of the sulfuric acid used, point is reached.

Blank test that the reagents are free from nitrogen, carry out a blank test distillation and titration) using 1 g of sucrose (3.13) in place of the

Calculation of results of crude protein is calculated according to the following formula:

× c × 0.014 × 100 × 6.25

m

(ml) of NaOH (3.9 or 3.10) used in the blank test.

(ml) of NaOH (3.9 or 3.10) used in the sample titration.

Concentration (mol/l) of sodium hydroxide (3.9 or 3.10).

(g) of sample. Verification of the method Repeatability difference between the results of two parallel determinations carried out on sample must not exceed:

0,2% in absolute value, for crude protein contents of less than 20%; 1,0% relative to the higher value, for crude protein contents from 20% 40%; 0,4% in absolute value, for crude protein contents of more than 40%.

Accuracy the analysis (digestion, distillation and titration) on 1,5 to 2,0 g of (3.12) in the presence of 1 g of sucrose (3.13); 1 g acetanilide consumes sulfuric acid (3.5). Recovery must be at least 99%.

Observations Apparatus may be of the manual, semi-automatic or automatic type. If the requires transference between the digestion and distillation steps, this transfer must be carried out without loss. If the flask of the distillation not fitted with a dropping funnel, add the sodium hydroxide immediately connecting the flask to the condenser, pouring the liquid slowly down 8.2 If the digest solidifies, recommence the determination amount of sulfuric acid (3.4) than that specified above. 8.3 For products with a law nitrogen content, the volume of sulfuric to be placed in the collecting flask may be reduced, if necessary, to 10 make up to 25 ml with water.