Determination of iodide in milk and milk powder via ion chromatography with pulsed amperometric detection applying in-line stopped flow dialysis

Iodine is an essential trace element for humans development.

Iodine is an essential trace element for humans development.

It is a component of the thyroid hormone thyroxin, which regulates the body’s metabolic state and the growth and development in children. Iodine deficiency is an important health problem throughout much of the world. The dietary uptake of sufficient trace amounts of iodide is therefore necessary for mental and physical development. Important sources of Iodide are seafood, dairy products, iodized table salt and processed foods like iodized bread. As with many other essential nutrients, intakes in excess of physiological requirements can produce adverse effects.

For infants, the only source of iodide is milk or infant formula. Hence, it is of vital importance that the iodide levels in milk are strictly monitored.

Iodine tends to be supplemented at farm level in the expectation of increasing cow health and fertility. In addition to that, iodine is commonly used to disinfect the cow teats prior to the milking process.

As there are many sources of iodine in the milk production process, many of them on farms outside of the final production control, there is a concern that such practices may result in high fluctuations of milk iodide.

Furthermore, fluctuations in milk will affect the ingredients composition for infant formulas. For traceability throughout the supply chain, a simple and robust method is required to monitor iodide levels in milk.

Summary

The objective of this study was to develop and validate a fast and reliable method for the quantification of low-level iodide in milk. Limited sample preparation requirements was an additional desire to ensure short turnaround time for results.

Many of the analytical techniques such as IC and ICP require purification steps to eliminate fats and proteins. Microwave digestion, alkaline extraction, acid digestion or precipitation with methanol/acetonitrile followed by ultracentrifugation are commonly used to prepare samples. The method developed here applies in-line, stopped flow dialysis, which reduces the manual handling required. Consequently, the total error is also significantly reduced.

The ion chromatographic determination was carried out on a medium capacity anion exchanger utilizing a nitric acid mobile phase followed by pulsed amperometric detection (PAD). The PAD detector is equipped with a wall jet cell on a silver working electrode and a silver/silver chloride reference electrode. A great deal of attention was given to finding the right volt-amperometric settings and measuring potential in order to have a robust method. Eliminating time- consuming electrode polishing procedures is a key consideration in selection of evaluation conditions. (Refer to addendum 4)

A multistep, short period, reduction potential was applied in order to optimize the cleaning efficiently without the formation of hydrogen gas. The method turns out to be extremely sensitive and reproducible and has a linear range from 0.1 to 20 ppb.

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White Paper IC BC-0001-092017: Determination of iodide in milk and milk powder via ion- chromatography with pulsed amperometric detection applying in-line stopped flow dialysis.

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