Functions of iodine in human body

Iodine first began being added to salt commercially in the United States in 1924 by the Morton Salt Company at the request of the government.Iodine is essential for healthy brain development in the fetus and young child. Iodine deficiency negatively affects the health of women, as well as economic productivity and quality of life.

Specifically, Iodine is a critical element used by your thyroid in being able to synthesize certain gland secretions which, among other things, influences your heart, metabolism, nerve responsesMost people need an additional source of iodine as it is found in relatively small amounts in the diet. Iodization is the process of fortifying salt for human consumption with iodine and is an effective strategy to increase iodine intake at the population level.

The public health goals of reducing salt and increasing iodine intake through salt iodization are compatible as the concentration of iodine in salt can be adjusted as needed. Monitoring the levels of iodine in salt and the iodine status of the population are critical for ensuring that the population's needs are met and not exceeded.About 90% of people who develop a goiter do so because of a lack of iodine in their diets

Determination of Iodine in Salt

Reaction 1 : Liberation of free iodine from salt

•          Addition of H2SO4 liberates free iodine from the iodate  in the salt sample.

•          Excess KI is added to help solubilise the free iodine, which is quite insoluble in pure water under normal conditions.

Reaction 2: Titration of free iodine with thiosulfate.

•          Free iodine is consumed by sodium thiosulfate in the titration step. 

•          The amount of thiosulfate used is proportional to the amount of free iodine liberated from the salt.

•          Starch is added as an indicator, and reacts with free iodine to produce a blue colour.

•          The loss of blue colour indicates that all remaining free iodine has been consumed by thiosulfate.

Reagents

•          0.005M Sodium thiosulfate (Na2S2O3):   Dissolve   1.24g Na2S2O3.5H2O in 1000mL water.

•          2N Sulfuric acid (H2SO4): Slowly add 6mL concentrated H2SO4 to 90mL water.   Make to 100mL with water.

•          Note:  Always add acid to water, not water to acid, to avoid excess heat formation and spitting of acid.  Stir solution while adding acid.

•          10% Potassium iodide (KI): Dissolve 100g KI in 1000mL water.  Store in a cool, dark place. 

•          Starch indicator solution: Make 100ml of a saturated NaCl solution, by adding NaCl to approximately 80mL water in a beaker, with  stirring  and  /or heating, until  no  further  solid  will dissolve. 

•          Weigh 1g  soluble starch into a 100 ml beaker, add 10ml water, heat  to dissolve.  Add saturated NaCl solution to the hot starch solution to make up to 100ml

Procedure

•          Step 1.   Weigh 10g of the salt sample into a 250mL Erlenmeyer flask with a stopper.

•          Step  2.   Add approximately 30mL water, swirl to dissolve salt sample.

•          Step 3. Add water to make volume up to 50mL.

•          Step 4. Add 1 mL 2NH2SO4.

•          CAUTION- Do not pipette by mouth.

•          Step 5. Add 5mL 10%KI.  The solution should turn yellow if iodine is present.

•          CAUTION- Do not pipette by mouth.

•          Step 6. Stopper the flask and put in the dark (cupbord or drawer) for 10 minutes.

•          Step  7. Rinse and fill burette with 0.005M Na2S2O3, and adjust level to Zero.

•          Step  8. Remove flask from drawer, and add some Na2S2O3 from  the titration  burette until the solution turns pale yellow  (flask B shown in figure 11.4).

•          Step  9. Add approximately 2mL of stach indicator  solution  (the solution  should turn dark purple) and continue  titrating  until the  solution  becomes  pink, and  finally  colourless.   (Colour sequence of titration is shown in flasks C,D and E, figure 11.4).

•          Step  10.  Record  the level of thiosulfate in the burette  and convert to parts per million (ppm) using the conversion table  in Appendix 11-3.

•          NOTE : Analysis time is approximately 20 minutes per sample.