These procedures involve the following Kjeldahl methods: Nine laboratories analyzed nine pairs of blind duplicate raw milk samples for percent protein by these prescribed methods.
Protein Crude Determination in Animal Feed: Copper Catalyst Kjeldahl Method.
Association of Official Analytical Chemists. The methods described are applicable for determination of nitrogen N in forages.
The method consists of three basic steps: Kjeldahl flasks, to mL Kjeldahl digestion unit with fume removal manifold Kjeldahl distillation apparatus - Kjeldahl flask connected to distillation trap by rubber stopper.
Distillation trap is connected to condenser with low-sulfur tubing. Outlet of condenser should be less than 4 mm diameter. Erlenmeyer flask, mL Analytical balance, sensitive to 0. After standardizing hydrochloric acid and sodium hydroxide, check one against the other by titrating one with the other and calculating normality.
Always add acid to water unless otherwise directed in method. Wear face shield and heavy gloves to protect against splashes. If acids are spilled on skin, immediately wash with large amounts of water.
Sulfuric acid and sodium hydroxide can burn skin, eyes and respiratory tract severely. Wear heavy rubber gloves and face shield to protect against concentrated acid or alkali.
Use effective fume removal device to protect against acid fumes or alkali dusts or vapors. Always add concentrated sulfuric acid or sodium hydroxide pellets to water, not vice versa.
Concentrated sodium hydroxide can quickly and easily cause blindness. If splashed on skin or in eyes, flush with copious amounts of water and seek medical attention.
Keep baking soda and vinegar handy in case of chemical spills. The sulfur oxide fumes produced during digestion are hazardous to breathe.
Digests must be cool before dilution water is added to avoid a violent reaction during which the acid can shoot out of the flask.
Likewise, the diluted digest must be cool before sodium hydroxide is added to avoid a similarly violent reaction. Digestion Weigh approximately 1 g ground sample into digestion flask, recording weight W to nearest 0. Include reagent blank and high purity lysine HCl as check of correctness of digestion parameters.
Weigh a second subsample for laboratory dry matter determination. Add 15 g potassium sulfate, 0.
Then add 20 mL sulfuric acid. Place flask on preheated burner adjusted to bring mL water at 25oC to rolling boil in 5 min. Cool, cautiously add mL distilled water and cool to room temperature less than 25oC.
If bumping occurs during distillation, volume of water may be increased to ca. Distillation Prepare titration flask by adding appropriate volume VHCl accurately measured acid standard solution to amount of water so that condenser tip is immersed try 15 mL acid and 70 mL water if undecided. For reagent blank, pipet 1 mL of acid and add approximately 85 mL water.Title Determination of Protein Content Using Kjedahl and Titration Introduction Proteins are polymers.
They are the source of dietary amino acids and are used for growth and maintenance of . 6. Analysis of Proteins. Introduction. Determination of Overall Protein Concentration. Kjeldahl method As with the Kjeldahl method it is necessary to convert the concentration of nitrogen in a sample to the protein content, using suitable conversion factors which depend on the precise amino acid sequence of the protein.
To determine specific length of boil time needed for analysis conditions in your laboratory, select high protein, high fat milk sample and determine protein content using different boil . Protein is determined by the analysis of the nitrogen content.
From this, the protein content is calculated.
Protein consists of amino acids which contain nitrogen (N) in the amino group. Forward This booklet has been developed to serve as a technical companion in the selection and use of Kjeldahl nitrogen determination methods and apparatus. The Kjeldahl method of nitrogen analysis is the worldwide standard for calculating the protein content in a wide variety of materials ranging from human and animal food, fertilizer, waste water and fossil fules.