Experiment Report on Determination of Total Nitrogen in Water Samples

This report details an experiment to determine the total nitrogen content in water samples using the Kjeldahl digestion technique, which converts nitrogen to ammonia. The experiment involves two phases: ammonia determination and organic nitrogen determination. The first phase adjusts the pH of the solution to remove unwanted compounds through distillation. The second phase focuses on eliminating nitrates and nitrites. The procedure includes calibration using ammonia solutions, distillation of the water sample, and measurement of absorbances using a spectrophotometer. Sulfuric acid is used to decompose interfering substances, and sodium hydroxide aids in converting ammonium ions to ammonia. The results are discussed in terms of the proportional relationship between absorbance and concentration, and the limitations of the method are addressed, along with potential improvements such as using ion exchangers of higher capacity. The experiment successfully determined the nitrogen concentration, which is crucial for assessing water quality and developing pollution control policies. Desklib provides additional resources for students studying environmental science.

Running head: DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES
Determination of total nitrogen in water samples
Student’s name
Institution affiliation

DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES 2
ABSTRACT
The experiment is a standard method used in the determination of organic nitrogen in water
samples, based on the Kjeldahl technique of digestion where nitrogen is converted to ammonia.
(Davis, Shokouhian, Sharma,and Minami, 2012)The experiment was done in two phases, (a)
determination of ammonia and (b) determination of organic nitrogen. The first step involved
altering the PH of the solution to eliminate unwanted compounds in water through distillation.
(Kagimoto, Taguchi, Fukumoto, and Ohno, 2010)

DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES 3
INTRODUCTION
The experiment is the most straightforward and easy way to determine the amount of
nitrogen in water. Excess nitrogen concentrations often result from factors such as fertilizer
runoff, and combustion of fuels. (Xu, Paerl, Qin, Zhu, and Gaoa, 2010) Nitrogen in water exists
as both inorganic and organic species where the inorganic forms can be nitrite and nitrates
whereas the reduced form is ammonia. The reduced forms can be in diverse complexes including
amino acids, urea, aldehydes, and ketones. Their separation is therefore difficult as they are
capable of forming the same color with the reagent used. This technique utilizes the principle of
dissociation of nitrogen to complexes like amino acids and proteins. (Chapman, Fromme, Barty
White, Kirian,Aquila, Doak,2011). Total determination of TKN together with the sum of nitrates
and nitrites is usually obtained.
Equal molar concentrations of hydroxide and persulfate ions are adapted to yield a
solution with a given PH at a distinct ration of dilution. Nitrogen oxidation to nitrate occurs with
continued digestion at alkaline condition initially present. Bisulfate ions result from the thermal
decomposition of the ions leading to a drop in PH of the reaction mixture. There is a subsequent
increase in acidity of digest mixture and phosphorus is hydrolyzed to orthophosphate. In most
cases, a column of high capacity is vital in minimizing chromatographic interferences caused by
chloride, and chlorate (via chloride oxidation). A laboratory blank is helpful in detecting
whether the interventions exist within the sample, reagents or the lab instruments.
The reagent used here consisted of:
 magnesium oxide in fine powder form
 solution of ammonium for calibration

DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES 4
 A stock solution of ammonium made by diluting 3.18g of ammonium chloride in
1litre of deionized water.
 Nessier reagent made of 5% potassium iodide solution in saturated mercury iodide and
12g of sodium hydroxide.
The second phase of the experiment involved the elimination of nitrates or nitrites present in
the water. The reagents used here include:
 Sulfuric acid with low nitrogen content.
 A catalyst made from mixing 4g selenium, cupric sulphate and anhydrous sodium
suphate.
 Phenolphthalein indicator prepared by dissolving and stirring 1g of phenolphthalein in
100ml alcohol followed by water addition.
 Sodium hydroxide solution.
PROCEDURE
(a) Determination of ammonia
Calibration
 0.1, 2,4,6, and 8ml of ammonia solution was added to seven 50ml volumetric flasks
respectively
 Each of the containers was then diluted with 50ml of deionized water together with the
addition of 1ml Nessier reagent. Care was taken to avoid possible ingestions and
irritations from the toxic nature of the reagent
 The solution was stirred well and left for 10minutes to encourage the appearance of color.
The absorbances of each solution were measured at 410nm using 1cm cell and deionized
water as the reference.

DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES 5
 The reading obtained was then deducted from absorbance readings of solution that did
not contain ammonia. A curve of absorbance against nitrogen was calibrated to account
for the differences in absorbances.
Analysis
1. Deionized water was distilled through the solution obtained for purposes of
eliminating any ammonia. The water was further cooled and discarded.
2. 100ml of the sample was then added to round-bottom flask preceded by neutralization
with sodium hydroxide.0.3 g magnesium oxide was later added and deionized water
used to rinse the apparatus.
3. These were followed by connection of the flask to the condenser where distillation
was done. Dry heating was avoided to prevent loss of the interfering substances.
4. The distillate collected was then diluted with water, and 50ml of it transferred to a
50ml volumetric flask. 1ml of nessier reagent was added and left for 10minutes to
facilitate color formation.
5. Measurement of absorbances at 410nm was done as in the calibration part, and further
dilutions were done in case of readings that fall out of the prepared curve range. The
difference between the readings and that of the blank were taken. The weight of
ammoniacal nitrogen was then calculated from the values in a litre of sample.
(b) Organic nitrogen determination
1. The balance from the determination of ammonia was transferred to 350ml Kjeldahl
flask followed by the addition of 1g catalyst and 10ml of alcohol.

DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES 6
2. Mixing was done with the addition of sulfuric acid preceded with boiling until the
color changed to green. Continued heating was done to eliminate nitrate and nitrites
that may have been retained.
3. Cooling was then done followed by dilution with 150ml of deionized water that was
free of ammonia. Ultra-heating was discouraged by continuous stirring of the solution
as cooling was done.
4. The solution was transferred to 1l round-bottomed flask that had been thoroughly
mixed; phenolphthalein indicator drops with sodium hydroxide in enough amount
was added to produce a permanent pink color.
Results and calculations
Table 1: calibration curve using UV-Vis at 410nm
Concentration (ppm)
1
2
3
4
5
Absorbance
0.021
0.056
0.118
0.183
0.259
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
0
0.05
0.1
0.15
0.2
0.25
0.3
concentration
absorbance

DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES 7
Discussion of results
From the experiment, sulfuric acid was used to decompose the interfering substances by
oxidation to give ammonium sulfate, a reduced form of nitrogen. Digestion aimed at breaking all
the nitrogen bonds leading to a subsequent change to ammonia. Sample transformation to a black
foam accounts for the change fastened by an increase in temperature. Distillation facilitated the
conversion of ammonium ions to ammonia with the help of sodium hydroxide. Different
substances at varying concentrations, absorb light at different rates within the same wavelength;
hence, the proportional increase in absorbance with an increase in concentration.
The Nessier reagent is made up of salts to increase the boiling temperature of sulfuric
acid and improve the efficiency of the digestion process. Despite this, the method consumes a lot
of time, and the results may not be accurate. Alternatively, alkaline peroxo disulfate can be used
in the digestion process where potassium peroxodisulphate is used to oxidize the nitrogen under
high pressure and temperature. The sole product is nitrate that has its concentration determined
by chromatographic techniques. (Dabrowski, Murray, Ashton, Leaner, 2009).
Some of the procedural steps that could be improved include using ion exchangers of
higher capacity to counter cases of values falling out of the calibration curve. These columns are
capable of resolving both phosphates and nitrates from the sample. (Ito, Kohno, Nakamura,and
Ohno, 2012). All the same, it is clear that the experiment has adhered to the principle hence
correct determination of nitrogen.
Conclusion
The experiment was successful in determining the amount of nitrogen present in sample
water. The difference in absorbances between the sample with ammonia and that which was

DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES 8
ammonia-free depicted nitrogen concentration. The advantage of this method is that it can be
used to deduce the quality of water and therefore the extent of contamination. (Huang,Sillanpää,
Duo, and Gjessing,2016). This is crucial in developing policies that help counter water
pollutions in different parts of the world.The disadvantage that comes with this method is that
not all the nitrogen in compounds that are organic can be quantitated.

DETERMINATION OF TOTAL NITROGEN IN WATER SAMPLES 9
References
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Chapman, H. N., Fromme, P., Barty, A., White, T. A., Kirian, R. A., Aquila, A Doak, R. B.
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Kagimoto, J., Taguchi, S., Fukumoto, K., & Ohno, H. (2010). Hydrophobic and low-density
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Dabrowski, J. M., Murray, K., Ashton, P. J., & Leaner, J. J. (2009). Agricultural impacts on
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