Seasonal and regional variations of iodine in Danish dairy products determined by inductively coupled plasma mass spectrometry

The content of iodine in 72 samples of Danish dairy products was determined by direct flow injection (FI) sample introduction of whole milk into the ICP-MS instrument, or by bomb ashing of cream and cheese samples prior to the ICP-MS measurement. The performance of the FI-based method was superior to the bomb ashing method in terms of the limit of detection which was 9 ng g(-1) and 60 ng g(-1) for the two methods, respectively, and in repeatability which was 8.4 and 45 ng g(-1), respectively.

Both methods of analysis were accurate as demonstrated by analyses of the CRM 063R Skim Milk Powder. The iodine content of the milk samples varied between 42-162 ng g(-1). A geographical difference in the iodine content showed. that milk from Jutland contained less iodine than milk from Sealand. This can be explained by the lower natural iodine content in the drinking water resources in Jutland.

A temporal difference showed a general increase in iodine concentration in milk from all regions during the winter months over the summer months. This can be explained by the use of iodine-enriched fodder during the winter months. The poorer repeatability of the analyses of cream and cheese samples obscured any possible geographical and temporal variation of iodine in these samples.