GB/T 6432-2018Determination of crude protein in feeds—Kjeldahl method (English PDF)

Foreword

This Standard was drafted in accordance with the rules given in GB/T 1.1-2009.

This Standard replaces GB/T 6432-1994 Method for the determination of crude protein in feedstuffs.

Compared with GB/T 6432-1994, the main technical changes, except editorial changes, are as follows.

-- Modify the standard name (see cover);

-- Modify the scope of application (see Chapter 1);

-- Add provisions on significant figures of calculation results (see Chapter 8).

1 Scope

This Standard specifies the Kjeldahl method for the determination of crude protein in feeds.

This Standard applies to the determination of crude protein in feed raw materials, compound feeds, concentrated feeds, concentrate supplements and additive premixed feeds.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies to this document. For undated references, the latest edition (including any amendment) applies to this document.

GB/T 601, Chemical reagent - Preparations of reference titration solutions

GB/T 6682, Water for analytical laboratory use - Specification and test methods

GB/T 14699.1, Feeding stuffs - Sampling

GB/T 20195, Animal feeding stuffs - Preparation of test samples

3 Principle

The sample is digested by sulfuric acid under the action of the catalyst, and the nitrogen-containing compound is converted into ammonium sulfate. Add alkali to distill to make ammonia escape;

4 Reagents or materials

Unless otherwise stated, only use analytical reagents.

4.1 Water. GB/T 6682, grade 3.

4.2 Boric acid. chemical pure.

4.3 Sodium hydroxide. chemical pure.

4.4 Sulfuric acid. chemical pure.

4.5 Ammonium sulfate.

4.11 Hydrochloric acid standard titration solution. c(HCl) = 0.1 mol/L or 0.02 mol/L, prepared and calibrated according to GB/T 601.

4.12 Methyl red ethanol solution. Weigh 0.1 g of methyl red; use ethanol to dissolve and dilute to 100 mL.

4.13 Bromocresol green ethanol solution. Weigh 0.5 g of bromocresol green; use ethanol to dissolve and dilute to 100 mL.

5 Instruments and equipment

5.1 Analytical balance. sensitivity 0.000 1g.

5.2 Boiling sterilizer or electric furnace.

5.3 Kjeldahl flask. 250 mL.

5.4 Boiling and sterilization tube. 250 mL.

6 Sample

Take representative feed samples according to GB/T 14699.1; use the quartering method to reduce the sampling.

7 Test steps

8 Test data processing

The crude protein content in the sample is expressed in mass fraction w, and the value is expressed in mass fraction (%), and calculated according to Formula (1).

9 Precision

Under repeatability conditions, the ratio of the absolute difference between two independent measurement results and their arithmetic mean TO the mean shall meet the following requirements. […]