The method, called Thermometric Endpoint Titration does not rely on chloride content (salt is made up of sodium and chloride), which has been the main titration method for measuring sodium. This can lead to errors according to the study, published in the Journal of Agricultural Chemistry and Environment.
Titration is used to measure the volume of one solution that exactly reacts with another solution. It is well-established as the standard method for quantitative analysis.
TET uses a sensor (thermometer) to detect the endpoint of the titration reaction. This relies on a change of temperature in solution, regardless of the actual temperature, so it doesn’t need to be calibrated.
The study states that not all sodium in food has chloride as a counter-ion, as manufacturers routinely add salts of sodium, for example flavour enhancers or preservatives. Also there are non-sodium chloride sodium sources from the foods themselves.
Therefore, the “the titrimetric determination of sodium by calculation from chloride content is no longer acceptable”.
Other methods that don’t rely on chloride content were described as “difficult and complex” and therefore unsuitable for routine measurement by less-skilled operators.
The challenge was to use existing chemistry and convert it into a relatively easy titration method suitable for routine process and quality control in food manufacturing facilities.
They identified a viable method using a titrant solution of aluminium ions accompanied by potassium ions in a particular concentration ratio.
Sodium reacts exothermically with aluminium in the presence of an excess of potassium and fluoride ions to form “elpasolite” (NaK2AlF6), forming a “robust, reliable analytical procedure suitable for routine process control”.
The study did highlight that calcium may interfere in the determination of sodium in some foodstuffs but at such a level that manufacturers could neglect this error for routine process.
The researchers concluded that the procedure depends on the amount and suitability of the sample being tested.
Industry and health
The health impact of high levels of sodium has spurred food manufacturers to reduce salt content in products.
Barbara Gallani is director of regulatory, science and health at the UK Food and Drink Federation (FDF). She told Foodnavigator.com that to complement this reformulation work, FDF members recognise the importance of providing accurate information on salt as a powerful way of helping consumers make better-informed choices and improving their overall food literacy choice.
She added: “This is why UK food and drink manufacturers have been providing consumers with clear nutrition information on both the front and back of food labels for many years.”
Source: Journal of Agricultural Chemistry and Environment
Vol. 3 No. 1B, 2014, pp. 20-25. doi: 10.4236/jacen.2014.31B005.
"Novel method for determination of sodium in foods by thermometric endpoint titrimetry (TET)"
Authors: T. Smith and C. Haider