Analysis of iodide in table salt

Table salt (sodium chloride) is a critical 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.

Iodide as potassium iodide is a key component that may or may not be present in table salt depending whether or not the salt is iodised, and salt manufacturers require a simple, reliable way of quantifying its presence.

In plants where both non-iodised and iodised salt are produced within the same facility, non-iodised salt can be checked for contamination to ensure that no iodide is present.

The potassium component could also be determined with ion chromatography using a suitable eluent and separation column. Ion chromatography with Metrohm represents a robust, precise quantitative technique for the analysis of iodide in a variety of different sample matrices that include table salt.

In recent years the cost of ion chromatography instruments have fallen and they now represent a cost effective analytical solution to alternative techniques.

Historically iodide analysis was often performed chromatographically with electrochemical detection, but it can be performed using suppressed conductivity detection with a sensitive detector and a suitably selective, high capacity separation column.

Some information about salt.

The primary commercial deposits of salt in the United Kingdom are found in areas of Northern Ireland, Cheshire, and Cleveland with only a small number of manufacturers.

The salt production methods employed by the Romans in Britain were simple and consisted of brine evaporation which is still the basic principle of salt production today.

Saturated brine with around ten times the salinity of sea water is pumped from deposits deep underground, before the brine is treated and boiled in energy efficient vacuum evaporator plants where the salt crystals start to grow.

These are then extracted and dried using a rotary filter, before optimisation to meet specific customer requirements as necessary, then storage in silos prior to despatch.

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 typical male weighing 70kg contains around 92 grams of sodium.

Salt depletion is usually associated with dehydration; an active worker can lose up to eight litres 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 of people in the United Kingdom 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.

Salt crystals are cubic in form and table salt consists of tiny cubes bound tightly together through ionic bonding of the sodium and chloride ions. The addition of iodide to table salt.

, Iodine actually applies to the elemental mineral but is often used to describe any compound of iodine such as potassium iodide which has a more active influence on the thyroid gland.

Potassium iodide is often used to add iodine to salt and the technology required to iodise salt is inexpensive - but less developed countries may lack high quality salt manufacturing and packaging technologies.

Potassium iodide tends to dissociate into free iodine so dextrose is often added to the salt to act as a stabiliser.

Iodine is needed because of the thyroid gland in the neck, which produces two hormones (thyroxine and tri-iodothyronine) that are used by the body to control metabolism.

Without these two hormones one can start to feel tired, cold and depressed.

Iodine is an important element in these two hormones and without iodine the thyroid gland can not produce them.

When starved for iodine, the thyroid gland swells; this is known as goiter.

The human body does not need much iodine, and contains around 20 to 25 milligrams of the element.

In certain parts of the world the soil contains no iodine hence the plants lack iodine and iodine deficiency can then be a problem.

As a result of the work of David Marine (1880-1976) and co-workers, many countries launched a goiter prevention programme using iodised salt.

Salt producers have played a key role in combating iodine deficiency disorders throughout the world.

In 1983 there were an estimated 400 million iodine deficient people in less developed countries of the world, and another 112 million in more developed regions.

Various studies have concluded that iodine deficiency disorders can be especially harmful to pregnant women, their foetuses and newborn babies.

Research conducted since by the medical community has also identified a more serious problem in possible mental retardation as a consequence of a deficiency in iodine.

Recent terrorist attacks have had people concerned about potential future attacks with radioactive material.

This has been much information misreported about the role of potassium iodide after an incident involving radioactive material.

If radioactive iodine is not present then taking potassium iodide will have no effect whatsoever.

If radioactive iodine is around, then consuming potassium iodide will help protect the thyroid gland from the radioactive iodine by saturating it such that inhaled or ingested radioactive iodine will not be accumulated, but it will not defend people from other radioactive substances that may be present along with the radioactive iodine.

Radioactive iodine releases radiation that in high concentrations can damage the cells of the thyroid gland which can lead to thyroid cancer or other diseases associated with the thyroid.

Following the Chernobyl incident some 10.5 million children and seven million adults were administered potassium iodide with side effects such as nausea and vomiting occurring only in 0.35% of children and 0.2% of adults.

The use of salt in food.

Salt is the world's oldest known food additive and brings out natural flavours making certain foods more acceptable to the human palette.

It is widely used in dairy products, meat and fish products, canned vegetable, bakery products, confectionery, pickles and sauces.

Salt preserves foods by creating a hostile environment for certain micro-organisms; in food salt brine dehydrates bacterial cells, alters the osmotic pressure and inhibits bacterial growth and spoilage.

Salt acts as a texture aid strengthening the gluten in bread dough to provide a uniform grain, texture and dough strength.

With the presence of salt, gluten holds more water and carbon dioxide allowing the dough to expand without tearing.

In cheese, salt can develop the rind hardness and helps produce a desirable even consistency.

Salt acts as a binder by helping to extract the proteins in processed meats providing strength between adjacent pieces of meat increasing the water binding properties and reducing cooking losses.

In baked products, salt can control fermentation by retarding the rate at which fermentation occurs and is used in the pickle and cheese making processes.

Salt can be used with materials such as sugar and nitrite as a colour developer in the production of ham, bacon and sauerkraut to make the finished product more appealing to the consumer.

There is evidence that a high salt diet may be detrimental for certain people such as those with high blood pressure and many pressure groups support campaigns urging a reduction in intake.

The view of the UK food industry from the Food and Drink Federation from a statement made during 1998 was that "there is no consensus view that the health of the general population would benefit if the salt intake were reduced".

As is often the case, one obtains different views when speaking to experts in the medical community compared to those in the food industry.

It should be said that many UK companies have been gradually reducing the amount of salt in their products and one well known manufacturer has reduced the amount of salt in their baked beans by 15% over the last decade. What is ion chromatography? Chromatography is a method for separating mixtures of substances using two phases, one of which is stationary and the other mobile moving in a particular direction.

Chromatography techniques are divided up according to the physical states of the two participating phases.

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.

Method for the determination of iodide in table salt.

1g of the dried analytical sample was weighed accurately into a 100ml volumetric flask before being up to the mark with deionised water.

The sample was sonicated briefly in an ultrasonic bath to aid homogeneity.

The diluted sample was injected directly into the Metrohm 761 Compact IC and the response for the peaks recorded using a sodium carbonate/sodium bicarbonate/acetone eluent with the Metrosep A Supp 5 analytical column.

The calculation was carried out automatically using integration software IC Net 2.2 against a previously prepared calibration plot.

There are no external displays or switches on the instrument, all the hardware is fully controlled via a single RS232 connection between the IC and the PC.

All the instrument parameters can be called upon with a click of the mouse.

The 761 Compact IC comprises a low-pulsation dual-piston pump, pulsation dampner, electromagnetic injection valve, two-channel peristaltic pump suppressor module, conductivity detector, eluent organiser as well as a data recording and processing module.

All the components that come into contact with the eluent and sample are metal-free.

The detector is the heart of every ion chromatography instrument.

The Metrohm detector's temperature varies by less than 0.01C and can be optimally adapted to the ambient conditions.

This outstanding temperature stability reduces interference and allows exact conductivity measurements.

The iodide content in the sample of table salt analysed was found to be of the order 2.3gl-1.

It can be seen from the chromatograph above that the large chloride peak at eight minutes presents no problem to the high capacity Metrohm column and is well removed from the iodide peak. Conclusion.

Ion chromatography as an analytical technique has seen an enormous surge in popularity, due partly to the simplicity of many of the methods as well as other factors such as market forces driving down the expenditure costs of the equipment and an improved instrument power.

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.

The low running costs of ion chromatography with Metrohm instruments are surprisingly low requiring only the acquisition of chemicals required for the eluent as well as a clean, reliable source of deionised water for preparation of the standards and samples.

Ion chromatography is a clean technique in that all the reagents are enclosed, its robustness and reliability are assured demonstrating precisely the reason why it is rapidly becoming the method of choice for many analysts in a plethora of different industries and is eminently suited to the analysis of iodide in table salt.