COLORIMETRIC METHOD FOR SODIUM

When I hear the word sodium, the first thing that enters my mind is salt. But let us tackle about sodium or salt inside our body. Yes, salt inside our very own body.

Sodium is the most abundant cation in the cell, it represents about 90% of all extracellular cations and it is largely determinate the osmolality of the plasma. The concentration of sodium in plasma depends on the intake and secretion of water. Our kidneys have the ability to conserve or to excrete large amounts of sodium, by means of filtrating the blood and the sodium is reabsorbed by the proximal tubule and some are in loop of henley and distal tubule.

There are cases that deals with the amount of sodium in our body. Hypernatremia and Hyponatremia. Hypernatremia is the term used for the result of excess loss of water which is comparative to sodium loss, decrease in water intake and increase in sodium intake. The symptoms are most commonly involved to the central nervous system which result to mental status, lethargy, fever, nausea or vomiting, edema, malnutrition and nephritic syndrome. Hyponatremia is the result for low level of sodium that manifested in prolong vomiting persistent diarrhea, salt-losing nephritis metabolic acidosis.

Now the question is, how can we determine the level of sodium?

There are two chemists named Barrensheen and Messiner had portrayed a colorimetric method that is applicable for serum or other biological fluids.


The result will depend on the elimination of free acids and phosphates with zinc acetate and hydroxide in the presence of 50% alcohol. The sodium is then precipitated as the triple acetate with uranium and zinc. The uranium in the precipitate formed is estimated colorimetrically with potassium ferrocyanide. The standard color is attained by submitting a standard solution of sodium to the equal treatment as the unknown. Another way is by using a standard solution of the triple acetate.

Reagent:
Alcohol zinc acetate with zinc hydroxide
Alcohol uranyl zinc acetate reagent
95% alcohol saturated with the triple acetate
20% potassium peroxide
Standard sodium chloride
Standard triple acetate

Procedure:
1. Using a test tube take an amount of the unknown solution containing 0.04-0.16 mg of sodium then dilute to 2 cc with water and add 4 cc of the alcoholic zinc acetate reagent. Stir and cover with the use of a rubber cap.
2. Allow it to stand at room temperature for 2-3 hrs and leave at 0° overnight.
3. Centrifuge it and transfer 3 cc of the supernatant fluid into another test tube. Add 4 cc of the uranyl zinc acetate reagent and stir it with the use of a glass rod until precipitate is formed.
4. Cover it with rubber cap and allow it to stand for 1 hour at 0°.
5. Centrifuge it and pour off the liquid obtained and drain the tubes by inverting it on a filter-paper and wash once with 5 cc of the ice-cold alcohol saturated with the precipitate. The precipitate should be stirred up.
6. Centrifuge and drain again. Liquefy the precipitate in water and transfer it to a 25 cc volumetric flask. If the precipitate is very huge, it indicates that the unknown contained more than 0-15 mg Na, transfer it to flask that can contain a greater volume.
7. there are two method for the standard its either take 1 cc of the diluted sodium chloride solution and do exactly the same method as the unknown and transfer it to a flask; the other method would be, take 5 cc of the dilute standard triple acetate solution in a 25 cc flask.
8. For the standard and unknown add 1 drop of glacial acetic acid and 0.5 cc of 20% potassium ferrocyanide, fill up with water up to the mark of the flask and allow it to stand for 3 mins.

For the calculations:

a.) using a standard NaCl solution
Na mg/100 cc= 20 (standard colorimeter reading)/reading of the unknown X 0.0786 X 100/vol. of unknown

b.) using the standardized triple acetate solution

Na mg/100cc= standard/unknown X 0.0786 X 100/ vol. of unknown

The intensity of the color developed by the potassium ferrocyanide is directly proportional to the amount of the triple acetate present.

reference ranges for sodium
Serum/Plasma : 136-145 mmol/L
Urine (24hr) : 40-220mmol/day (varies from the diet of the patient)
CSF : 163-150 mmol/L

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Remember excess and insufficient is always NOT GOOD.