Comparability of mineral oil testing for dry food and cardboard samples - Perspectives from different PT rounds

Mineral oil hydrocarbons (MOH) can be found in detectable levels in a multitude of foodstuffs. Therefore, chemical analysis of food for MOH gains importance. Different proficiency testing (PT) rounds on mineral oil testing have been performed in different matrices: cereals and rice as well as cardboard samples were examined. The laboratories participating in the PT rounds had to follow specific requirements for examination. The sample materials used contained different concentrations of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH). The PT results were statistically evaluated according to ISO 13528:2005 and additionally the HorRat(R) value was calculated to gain information on the comparability of the mineral oil testing. It could be shown that for the examined sample materials and under the chosen specifications for testing a comparable determination of the mineral oil content is possible within the required relative standard deviations. A useful analytical determination can be achieved with an acceptable relative standard deviation of <50% from a concentration of defined mineral oil fractions at >= 1 mg/kg in food. In the concentration range for MOH in food of between 1 mg/kg and 2 mg/kg, relative standard deviations of 20-40% were achieved. MOH concentrations of >= 2 mg/kg food were determined with good relative standard deviations of around 20%. Moreover, due to the results gained within this work a statement concerning the comparability for MOSH and MOAH contents below concentrations of 1mg/kg food is possible: under the chosen conditions for examination as part of this work, mineral oil determination below 1mg/kg food showed high variability. To gain reliable information with regard to consumer protection on the risk of mineral oil contents in this low concentration range further standardisation of the test method is indicated.