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Determine the Amount of Sodium in Water and Soil

Introduction: Sodium is the most abundant element on Earth and is widely distributed in soils, plants, water, and foods. Most of the world has significant deposits of sodium-containing minerals. Sodium ion is ubiquitous in water because of the high solubility of many sodium salts (EPA, 2003).

Sources of Sodium: The application of fertilizers and other agricultural products that contain sodium salts can increase the sodium in soils. Ground water and seawater contain sodium naturally. In food the majority of dietary sodium comes from sodium chloride added to food during food processing and preparation (EPA, 2003).

Sampling: The samples were collected from Lahore canal adjacent Punjab university campus at four intervals, each at a distance of 0.5km. A hand held sampler was used with a cork bottle. The sampler was suspended in the middle of the canal, cork pulled out with rope and samples were collected. The bottles were corked once out of the canal.  The samples were mixed to create a composite grab sample.

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For given Water Sample

Principle: A solution which contains cations of sodium is spayed into flame, the solvent evaporates and the ions are converted into atomic state. In the heat of the flame (temperature about 1800ºC) a small fraction of these atoms is excited but the relaxation of these excited atoms to the lower energy level is accompanied by emission of light with characteristic wavelength (Na: 589 nm). Intensity of the emitted light depends upon the concentration of particular atoms in flame.

Calibration: Set up the flame photometer for sodium measurements. Aspirate the blank solution and set the zero. Aspirate the 25ppm sodium standard solution and set the sensitivity to read 100. Aspirate the other standards in ascending order and construct a calibration graph.

Procedure: Rinse the Flame photometer with the blank containing only deionized water, the Flame photometer was calibrated to read 0.0. Run these standard solutions and sample in the flame photometer and note down the readings against the concentration. Each solution was allowed to be in the photometer exactly for 12 seconds before the reading was taken. These solutions were tested in the order of increasing concentration. Prepare a calibration curve for Na by using these reading. The reading of sample is plotted in calibration curve and the concentration of sodium in given water sample is evaluated.


Concentration (ppm) Emission
0 0
25 0.09
50 0.15
75 0.23
100 0.29
125 0.37
150 0.44
175 0.49
13 0.04


The concentration of Na+ in water is 13ppm.

For given Soil Sample

Sampling: The targeted field was sampled according to Quincunx sampling method in a Z-scheme. 16 grid nodes were sampled and each comprised of further three sub-samples. The distance between each grid node was 3.0 meters while the cores inter distance was 1.0 meters. Samples were collected from 25 grid nodes. The latitude and longitude were noted for each grid node. Before sampling the surface was carefully cleaned with a shovel to scrape away 1.0 inch of vegetation cover. The 10.0 cm diameter and 15.4 cm length metal core was then placed with a wooden wedge on top. The core was hammered into the soil to a depth of 7.5 cm, jerked and taken out along with the soil collected.  The four soil cores collected from each grid nod were transferred to a bucket and major humps were broken by hands. A lid was placed on the bucket and mixed thoroughly to achieve homogeneity. 1.5 kg sample was then transferred to pre labeled zip lock bag.


Sample preparation by acid digestion method: The soil sample was mixed thoroughly and 2.0g air dried soil sample was transferred to a conical beaker. 10 mL of 1:1 HNO3 was added, mixed and covered with a watch glass.The sample was heated to 95oC and refluxed for 10 to 15 minutes without boiling. The sample was allowed to cool and 5 mL of concentrated HNO3 was added, the watch glass replaced, and refluxed for 30 minutes. The solution was allowed to evaporate to 5 mL without boiling, while maintaining a covering of solution over the bottom of the beaker.

The sample was cooled; 2 mL of water and 3 mL of 30% H2O2 was added. The beaker was covered with a watch glass and returned to the hot plate for warming and to start the peroxide reaction. This was heated until effervescence subsided and the beaker was cooled. 30% H2O2 in 1-mL aliquots was continuously added with warming until the effervescence was minimal and the general sample appearance was unchanged.

5 mL of concentrated HCl and 10 mL of water was added, the beaker covered and put on the hot plate, and refluxed for an additional 15 minutes without boiling. After cooling, this was diluted to a 100 mL volume with water. This was finally filtered through Whatman No. 41 filter paper. The supernatant liquid was used for flame photometric analysis.

Standard preparation: Prepare a 10ppm sodium standard as follows: add 2ml of stock Sodium solution to a 100ml volumetric flask. Add deionized water and 1N neutral ammonium acetate up to the mark. Similarly prepare 20, 30, 40, 50 ppm sodium solution by diluting 500ppm of stock solution. For this 4, 6, 8, 10 ml of stock solution diluted with deionized water and 1N neutral ammonium acetate up to 100ml of solution. Prepare a blank solution by adding 5ml deionized water to a 1 liter volumetric flask and make up the volume to the mark with 1N neutral ammonium acetate. Now run the sample and record its meter reading. Read off the concentration of the sample from the calibration curve.

Observation and Calculation

Concentration (ppm) Emission
0 0
10 0.03
25 0.06
30 0.09
40 0.13
50 0.15
4 0.01

By calibration curve concentration of sodium in the =     4    ppm

The total sodium in mg/10g soil                                      = 4ppm × 200ml /1000ml

= 0.8mg/g of soil

Results: The amount of sodium in the given soil sample is ­­­­0.8 mg /g of soil.

Health Effects of Sodium:

Acute effects of high sodium intake may include dryness of mucous membranes, violent inflammatory reaction and ulceration in the gastrointestinal tract, along with dehydration and congestion of internal organs, particularly the meninges and brain. Sometimes Central nervous system disturbances may result in convulsions, confusion, and coma, and generalized and pulmonary edema is possible. Death may occur due to respiratory failure (EPA, 2003).

Effects of Sodium on Animals:

Sodium ion when ingested as sodium chloride has a low acute toxicity in animals. Doses that may cause lethality in animals range from around 3,000 to 8,000 mg/kg. Death has been only reported in case of severe alterations in fluid concentrations and/or fluid volumes (EPA, 2003).

Effects of Sodium on Plants:

Sodium is usually available for plants in the form of sodium chloride. NaCl causes an increase in plant height with low and medium concentrations and a decrease with the highest concentrations. No significant effect can be observed in the number of leaves or leaf area with low concentration, but a significant decrease can be observed with higher concentrations.Osmotic potential (O.P.) also decrease with the increase in concentrations, and in the duration of the stress periods. (Abdul Qados, 2011)


Category Max. limit Standardizing Agency
Drinking Water 200 mg/l WHO(1993)
Drinking Water 200 mg/l EPA
Drinking Water 180 mg/l ADWG
Drinking Water 200 mg/l EU
  1. Abdul Qados, A. M. (2011). Effect of salt stress on plant growth and metabolism. audi Society of Agricultural Sciences, 7-15.
  2. (2003). Drinking Water Advisory:Consumer Acceptability Advice and Health Effects Analysis on Sodium. Washington: Advisory, Drinking Water.


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