Exp 4 Kjeldahl Nitrogen

Experiment # 4 Kjeldahl Nitrogen

Title

To determine the amount of nitrogen in given water sample.

General:

All nitrogen present in the organic compounds may be considered as organic nitrogen. This includes amino acids, amines, amides, nitro derivatives and no of other organic compounds. In waters and waste water the form of nitrogen of greatest intrest are organic –N and ammonia-N, nitrates and nitrites. Organic nitrogen is defined functionally as organically bound nitrogen in tri negative state. In wastewaters organic-N include such natural materials like proteins, peptides , nucleic acids, urea and numerous synthetic organic materials. Organic nitrogen and ammonia can be determined together and have been referred as kjeldahl nitrogen.

Principle:

In the presence of H2SO4 , K2 S04 and CuSO4. Ammonia nitrogen of many organic materials is converted to ammonium sulfate. Free ammonia and ammonia nitrogen also are converted to ammonium sulfate. During sample digestion a cupric ammonia complex is formed. After this mercury ammonia complex in the digestion has been decomposed by sodium thiosulfate, the ammonia is distilled from an alkaline layer and absorbed in boric acid.

Basic Steps involved:

1) Digestion
2) Distillation
3) Titration. Titration theory:

The organic nitrogen is converted to ammonia nitrogen during the digestion. Boric acid is an excellent buffer. It combines with ammonia in the distillate to form ammonia and borate ions.
NH3 + H3  BO3–Æ NH4++ H2BO3-exp4
The ammonia then is measured by back titration with strong acid such as sulfuric acid.
Actually the acid measures the amount of boric ion present in the solution as follows.
H2BO3 -+H+-Æ H3BO3

Reagents:

  1. Digestion reagent ( dissolve 134g K2SO4 and 7.3g CuSO4 in about 800ml water carefully add 134ml coc H2SO4. Cool to room temperature, dilute to 1 lit with water . mix well keep at temp 200C to prevent vaporization).
  2. Phenolphthalein indicator
  3. Sodium hydroxide
  4. Mixed indicator solution
  5. Indicating boric acid solution
  6. Standard sulfuric acid titrant.
  7. Hydroxide thiosulfate reagent.

Procedure:

(a)    Digestion

  1. Take 280ml of sample in a kjeldahl flask.
  2. Add few glass beads to it then add 50ml digestion reagentexp4.1
  3. Mix , heat and continue boiling until solution remains 25-50ml.
  4. Cool it and add distilled water to it to make the volume 300ml.
  5. Add 0.5 ml phenolphthalein indicator.
  6.  Add 50 ml thiosulfate hydroxide reagent solution.
  7.  If pink colour does not appears then add more 50ml thiosulfate hydroxide reagent solution.

(B)      Distillation

  1. In collect the distillate in a flask containing boric acid solution.
  2. Collect 200ml distillate into 50ml boric acid solution

 (c)       Titration

exp4.2

  1.  Titrate it against 0.02N H2SO4 solution until colour changes from purple to green.
  2. carry the blank titration, following all steps of procedure.

Calculations:

Total Nitrogen (mg/L) = ((A-B)* 280) /ml of sample

 A= volume of H2SO4 used for sample= 6.9ml

B= Volume of H2SO4 used for blank= 0.1

Total nitrogen(mg/L)= 13.6 mg/L

Comments:

We have performed the experiment successfully and the amount of nitrogen in the gven water sample has came out to be 13.6mg/L Water with nitrite levels exceeding 1.0 mg/l should not be used for feeding babies. Nitrite/nitrogen levels below 90 mg/l and nitrate levels below 0.5 mg/l seem to have no nutrients are essential for plant and animal growth and nourishment, but the overabundance of certain nutrients in water can cause a number of adverse health and ecological effects.

Questions:

 1) What is Kjeldahl nitrogen?

All nitrogen present in the organic compounds may be considered as organic nitrogen. This includes amino acids, amines, amides, nitro derivatives and no of other organic compounds. In waters and waste water the form of nitrogen of greatest interest are organic –N and ammonia-N, nitrates and nitrites. Organic nitrogen is defined functionally as organically bound nitrogen in tri negative state. In wastewaters organic-N include such natural materials like proteins, peptides , nucleic acids, urea and numerous synthetic organic materials. Organic nitrogen and ammonia can be determined together and have been referred as kjeldahl nitrogen. Organic Kjeldahl nitrogen is defined as the difference obtained by subtracting the free- ammonia value from the total Kjeldahl nitrogen value. Also, organic Kjeldahl nitrogen may be determined directly by removal of ammonia before digestion.

2)  What is blue baby disease ?

 Blue baby syndrome (or simply, blue baby) is a layman’s term used to describe newborns with cyanotic conditions, such as

1) Cyanotic heart defects
Tetralogy of Fallot
Dextro-Transposition of the great arteries
2) Complete Atrio-Ventricular Septal Defect
Tricuspid atresia
3) Methemoglobinemia
4) Respiratory distress syndrome
Blue baby syndrome can also be caused by Methemoglobinemia. It is believed to be caused by high nitrate contamination in ground water resulting in decreased oxygen carrying capacity of hemoglobin in babies leading to death. The groundwater is thought to be contaminated by leaching of nitrate generated from fertilizer used in agricultural lands and waste dumps . It may also be related to some pesticides (DDT, PCBs etc), which cause ecotoxicological problems in the food chains of living organisms, increasing BOD, which kills aquatic animals.

3)  How ammonia nitrogen can be determined?

exp4.3

4)  Why hydroxide thiosulfate reagent is added in above experiment?

 To decompose mercury ammonia complex. In the presence of H2SO4 , K2 S04 and CuSO4 Ammonia nitrogen of many organic materials is converted to ammonium sulfate. Free ammonia and ammonia nitrogen also are converted to ammonium sulfate. During sample digestion a cuppric ammonia complex is formed and due to the addition of Hydroxide thiosulfate reagent , it will break the cpomplex and precipitate mercuric sulfide. Then the ammonia is distilled from an alkaline layer and absorbed in boric acid

5)  Write the significance of nitrogen test in Environmental Engineering.

Nitrogen is a dietary requirement for all organisms, because it is a constituent of all proteins and nucleic acids. Plants consists of approximately 7.5% nitrogen (dry mass).

Nitrogen is essential for plants, and can be found in air in large amounts. This elementary nitrogen cannot be taken up directly. Nitrogen must first be bound and converted, for instance to nitrate. This so-called nitrification process is carried out by bacteria, which convert ammonia and ammonium to nitrate and nitrite. This releases energy, and establishes a nitrate stock in soils that can be applied by plants.
When nitrogen fertilizers are applied, the plant nitrogen amount increases. A number of crops, such as spinach, even accumulate nitrogen compounds. When nitrogen fertilizers are applied outside the growing season, this is completely useless and negatively affects the environment. The fertilizers cannot be taken up or immobilized, causing them to end up in groundwater and drinking water. Nitrogen has a high spreading potential. A number of plants are relatively susceptible to NO2.
Nitric acid is an important constituent of precipitation. Together with H2SO4 it causes acid rain, which negatively affects crops and soils.
Nitrogen is an essential protein constituent, and is therefore present in animal tissue in large amounts. Elementary nitrogen has no direct effect on warm-blooded organisms. High nitrogen concentrations in air may lead to asphyxiation, because in this case the oxygen concentration decreases.
Nitrogen itself is not hazardous when present in water, and therefore does not cause any environmental damage. In seawater nitrates, nitrites and ammonia are dietary requirements for plankton, causing nitrogen concentrations to be lower at the surface than in the deep. At increasing nitrogen concentrations in surface layers, plankton production increases, leading to algal blooms. This may occur in any type of surface water. Large amounts of nitrate may cause eutrophication, which means an excess of nutrients resulting in oxygen deprivation and fish deaths (see oxygen and water). Nitrogen does not limit algal growth, because phosphorus is generally a limiting factor in water bodies. This means that phosphorus is the determining factor of algal spreading through surface waters. Oxygen deficits in surface water generally result in nitrate reduction to elementary nitrogen or nitrous oxide. This so-called denitrification process causes oxygen reserve releases, when oxygen supplies decrease to zero. In some cases nitrate may even be biologically reduced to ammonia. Ammonium compounds decrease the water oxygen concentration, because these are oxidized from nitrite to nitrate. Small concentrations of free ammonia may be toxic to fish.
Nitrification may also play an important role in water. This process means ammonia oxidation to nitrite and nitrate. The nitrite concentration is decreased, which is positive for higher plants, because nitrite is toxic at low pH values.
NOx compounds react with water to soluble nitric acid. This means that oceans can reduce atmospheric nitrogen oxide concentrations. PAN compounds (Peroxy Acetyl Nitrate) are derived from terrestrial environmental pollution, but may also be transported in the troposphere and in oceans. Eventually, these compounds are decomposed to NOx. The reaction mechanism is as described above.
There are some examples of toxic nitrogen compounds. NTA, which is generally complexed with heavy metals, can disturb electrolyte metabolism. In rats it may damage kidneys at concentrations above 14 mg/kg body weight. The LD50 value is 1.5 g/kg for rats and 0.75 g/kg for rhesus monkeys. It may cause chromosome defects in the in vitro system. For nitro aniline the LD50 for rodents is 1-3.6 mg/kg. The non-toxic concentration for fish is approximately 10 mg/L (48 h).
Nitrogen naturally has two stable isotopes. There are also six instable isotopes.

Health effects of nitrogen in water

The human body consists of approximately 2.6% nitrogen, which is a constituent of most proteins and nucleic acids. This means nitrogen is a dietary requirement. Nitrogen is the main constituent of the air we breathe. Increased nitrogen concentrations in air may cause asphyxiation, but mainly because it results in a lower oxygen concentration.
We mainly absorb nitrogen as proteins. These cannot be stored and are therefore directly converted to energy when not required. Nitrogen is excreted through the kidneys as urea. We also release nitrogen through the skin and the intestinal tract. When kidney failure occurs, one is incriminated with protein decomposition products. The calculation factor from nitrogen to protein in 6.25. This value does not represent protein digestibility.
Nitrates are not generally considered toxic, but at high concentrations the body may convert nitrate to nitrite. Nitrites are toxic salts that disrupt blood oxygen transport by disrupting haemoglobin to methemoglobin conversion. This causes nausea and stomach aches for adults. For young infants it may be extremely risky, because it rapidly causes blood oxygen deprivation.
The maximum recommended concentration for nitrate is 10 mg/L, and for nitrite the maximum level is 1 mg/L (EPA standards).
Nitrites and amines from protein-rich food form so-called nitrosamines, which are carcinogenic substances. This reaction may be prevented by the reducing and anti-oxidant properties of vitamin C.
Examples of toxic nitrogen compounds are PAN-compounds, which are fifty times more toxic than the nitrogen compounds these are converted from (nitriles and nitrilo compounds). NTA is not absorbed in the stomach, because it is complexed with heavy metals. It may however still disrupt electrolyte metabolism.
Nitrogen oxides play a more significant role in air than in water. These can cause breathing disorders. Nitrogen hydrogen acid fumes may cause irritations, heart problems and collapsing.

The Nitrogen Cycle

nitrogen_cycle

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