Today I visited my mother and as she was preparing lunch she asked me if I would like iodized or regular table salt in my soup. I went with the regular one because I never feel quite comfortable when there are artificial additives in my food. I guess it is because I have a hard time trusting the QC (Quality Control) departments of the food industry as a opposed to pharmaceutical ones. Then later today I decided to do some little “research” to see what analytical methods are currently used in QC of table salt production.

Background

Salt or sodium chloride is a crucial component in the human diet required for the correct functioning of nerves and muscles, the absorption of nutrients from the small intestine and to maintain the correct balance of fluids within the body. Ordinary table salt contains about 40% sodium, the brain continually monitors the amount of salt present in our bodies and sends instructions to the kidneys to either re-absorb or remove sodium as appropriate.The body of a male weighing 154 lb. contains around 92 grams of sodium. Salt depletion is usually associated with dehydration and an active worker can lose up to 8 liters of sweat per day and a failure to replenish the salt lost can have harmful effects on the body. It is estimated that the average salt intake is around 8 to 10 grams daily. The percentage of salt we consume from different foods depends on individual eating habits but typically about 10% of our salt intake is from foods which naturally contain salt and a further 10-20% is added by the individual at the table.

Iodized Table Salt

Sometimes iodine, as potassium iodide (KI), is present in table salt depending whether or not the salt is iodized. A lack of iodine in a person’s diet can result in a condition called goiter, in which the thyroid gland becomes enlarged. The thyroid gland uses iodine to produce two hormones thyroxine and tri-iodothyronine that are used by the body during metabolism. Without these two hormones one can start to feel tired, cold and depressed. The human body does not need much iodine and contains around 20 to 25 milligrams of the element. The addition of iodine compounds to table salt enables large numbers of people to get the iodine they need and that’s why salt manufacturers a reliable way of quantifying its presence. Also, in plants where both non-iodized and iodized salt are produced within the same facility, non-iodized salt can be checked for contamination to ensure that no iodide is present.

Analysis

Historically iodide analysis was often performed chromatographically with electrochemical detection; however, in recent years due to a fallen cost of ion chromatography the iodine analysis is more often performed using a selective, high capacity separation IC column with suppressed conductivity detection.

The term Ion Exchange Chromatography or Ion Chromatography (IC) is a subdivision of High Performance Liquid Chromatography (HPLC). A general definition of ion chromatography can be applied as follows: “ion chromatography includes all rapid liquid chromatography separations of ions in columns coupled online with detection and quantification in a flow-through detector”. A stoichiometric chemical reaction occurs between ions in a solution and a solid substance carrying functional groups that can fix ions as a result of electrostatic forces. For anion-chromatography these are quaternary ammonium groups. In theory ions with the same charge can be exchanged completely reversibly between the two phases. The process of ion exchange leads to a condition of equilibrium, the side to which the equilibrium lies depends on the affinity of the participating ions to the functional groups of the stationary phases.

Ion chromatography is a precise technique that requires only a very small amount of sample for the analysis and the quantified results obtained within a matter of minutes, so hopefully more and more salt manufactures will switch to IC method of iodine determination in their Quality Control laboratories.

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