Determination Of Protein Content Objective Biology Essay

Published:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Kjeldahl is an analytical method, which is suitable for quantitative determination of nitrogen in the trinegative state in organic compounds. This method was developed in 1833 by Johan Kjeldahl.

In this experiment, we analyzed the protein content, proteins are polymers of amino acids, which are important component of foods, because they are a major source of energy in our daily lives so that they are very essential to human health, also our body cannot synthesize the protein. Therefore, we need intake protein in our diet.

Kjeldahl method which involves 3 main steps, they are Digestion, Distillation, and Titration.

For digestion step, concentrated sulfuric acid was used, also there are in the presence of a catalyst, which helps amine nitrogen are converted to ammonium ions.

Organic N + H2SO4 → (NH4)2SO4 + H2O + CO2 + other sample matrix byproducts

For distillation step, the ammonium ions are converted into ammonia gas by heated and distilled with Sodium hydroxide. The ammonia gas is led into a trapping solution, such as hydrochloric acid, boric acid, which dissolves and becomes an ammonium ion once again.

(NH4)2SO4 + 2NaOH→2NH3 + Na2SO4 + 2H2O

For titration step, the amount of the ammonia that has been trapped in the receiving solution, it is titrated by standard solution to calculate the value of nitrogen.

2NH3 +2HCl → (NH4)2SO4 +H2SO4

There are two types of titration-back titration and direct titration. Both methods are testing for the ammonia which present in the distillate with a color change.

In our experiment, we use the back titration, since the ammonia has captured in a receiving flask with excess of measured standardized acid. The excess of acid which can keep the pH in acidic that means the indicator does not have color change until the solution is titrated with base.

(NH4)2SO4 +H2SO4 +2NaOH →Na2SO4 + (NH4)2SO4 + 2H2O

Apparatus

Analytical balance

Kjeldahl digestion and distillation apparatus-complete with heat source, traps, and block-tin, or equivalent noncorrosive tubing condensers (x1)

Kjeldahl flasks-500 mL. (x1)

Distillate receiving flasks-500 mL, or any convenient size.

Digestion rack (x1)

Shaker

Burette (x2)

5mL Pipette (x1)

Conical flask (x2)

Chemical used

Sodium hydroxide pellets

Anti-bumping granules

Methyl red indicator

0.5M Hydrochloric standard solution

0.5M Sodium hydroxide standard solution

0.5M Sodium carbonate

0.5M Potassium hydrogen phthalate

Potassium sulphate pellet

Copper(II) sulphate, anhydrous

Methyl red indicator

Sample used

Spiced pork cubes

Procedure

Standard preparation

Weigh 40g Sodium hydroxide NaOH, and dissolve in water

Dilute in the 100mL volumetric flask and make up with water to the mark.

To prepare 0.5M standard hydrochloric acid

Pipette 4.2mL 37% hydrochloric acid, dissolve in water

Dilute in the 100mL volumetric flask and make up with water to the mark

To prepare 0.5M standard Sodium hydroxide

Weigh 0.9999g NaOH, and dissolve in water

Dilute in the 250mL volumetric flask and make up with water to the mark.

To prepare 0.5M standard Sodium Carbonate

Weigh 0.9999g NaOH, and dissolve in water

Dilute in the 250mL volumetric flask and make up with water to the mark.

To prepare 0.5M standard Potassium hydrogen phthalate

Weigh 0.9999g NaOH, and dissolve in water

Dilute in the 250mL volumetric flask and make up with water to the mark.

Working Procedure

1.000 g of sample was weighed and put into Kjeldahl flask.

About 15 g of K2SO4, 0.04 g of anhydrous CuSO4, 20 mL H2SO4 and 0.5-1.0 g alundum granules were added into Kjeldahl flask.

The flask was placed on the digestion rack in an inclined position and then sample flask was heated at the 5 min boil rate until dense, white fumes clear bulb of flask.

Swirl gently and continue heating an additional 40 min after the liquid has become clear and colorless. The Kjeldahl flasks should be rotated a minimum of three times during the digestion.

About 300 mL of water was added cautiously, and cool to room temperature.

50mL 0.5M standard hydrochloric acid was transferred accurately into receiving flask.

An additional 0.5-1.0 g anti-bumping granules was added to cooled digestion flask.

Mix thoroughly and add 100mL 10M NaOH solution (pellets) to make strongly alkaline. Pour the alkali down the side of the Kjeldahl flask so that it does not mix quickly with the acid.

Immediately connect the Kjeldahl flask to the other end of the condenser tube and thoroughly mix the contents by shaking.

Apply heat at about a 7.5 min boil rate and distill until at least 150 mL of distillate have been collected.

Titrate the contents of the receiving flask with 0.1 M NaOH solution, using 3 or 4 drops of methyl red indicator.

Conduct a blank determination of all reagents simultaneously with the samples and similar in all respects. Correct for blank determined on reagents.

Writing Services

Essay Writing
Service

Find out how the very best essay writing service can help you accomplish more and achieve higher marks today.

Assignment Writing Service

From complicated assignments to tricky tasks, our experts can tackle virtually any question thrown at them.

Dissertation Writing Service

A dissertation (also known as a thesis or research project) is probably the most important piece of work for any student! From full dissertations to individual chapters, we’re on hand to support you.

Coursework Writing Service

Our expert qualified writers can help you get your coursework right first time, every time.

Dissertation Proposal Service

The first step to completing a dissertation is to create a proposal that talks about what you wish to do. Our experts can design suitable methodologies - perfect to help you get started with a dissertation.

Report Writing
Service

Reports for any audience. Perfectly structured, professionally written, and tailored to suit your exact requirements.

Essay Skeleton Answer Service

If you’re just looking for some help to get started on an essay, our outline service provides you with a perfect essay plan.

Marking & Proofreading Service

Not sure if your work is hitting the mark? Struggling to get feedback from your lecturer? Our premium marking service was created just for you - get the feedback you deserve now.

Exam Revision
Service

Exams can be one of the most stressful experiences you’ll ever have! Revision is key, and we’re here to help. With custom created revision notes and exam answers, you’ll never feel underprepared again.