Epithermal INAA: I in food samples Peter Vermaercke International Workshop IWIRAD 2005 on “Applications of the Ionising-Radiations to Industry, Health and Environment” 20 and 21 June 2005, Bucharest, Romania

I in food samples: EINAA is probably the only technique suited Why determination of I in food samples? Why EINAA? Validation results of EINAA Iodine concentrations in some typical food stuffs

Why determination of I in food samples? Iodine is an essential dietary element which is required for synthesis of the thyroid hormones. A shortage or an overdose of iodine creates thyroid disorder. The WHO and the Institute of Medicine at the National Academy of Sciences developed dietary reference intakes for iodine. These rise from 100 g/day for children up to 150 g/day for adults. The same institute also developed tolerable upper Intake levels for iodine intake: these range from 600 g/day for children up to 1000 g/day for adults.

150  g/day dietary reference intake 1000  g/day Tolerable intake level Determination of I is not an easy task The narrow range between minimum and maximum intake levels sets the requirements for the analysis technique for the determination of iodine in different sorts of foods: detection limits at a level of about 0.1 g an accuracy preferably better than 10 %

150  g/day 1000  g/day A lot of techniques have a problem monitoring I IRMM intercomparison study in milk powder: values ranged from 0,1 g/g to 0.6 g/g This is mainly due to the additional complications in chemical analysis when the solid samples are being digested with acids and the formation of volatile iodine species is not sufficiently suppressed.

Nuclear Techniques have to find a “niche” No sample preparation which eliminates the problems of the chemical techniques for I Only few samples (1 to 3) where the cost of ICP is not too low in comparison to INAA (for larger numbers we can not compete!) Customers for whom accurate results are needed: e.g. food federal agency who don’t want to take any risk (for them accreditation ISO is a basic requirement)

Using INAA: I hidden by Na, Cl, Mn, K, … 128 I 56 Mn 80 Br 24 Na 38 Cl 24 Na

Let’s have a look at the cross-section data E Cd =0,55 keV

128 I 56 Mn 80 Br 24 Na 38 Cl 24 Na Result using EINAA: suppression of the background leading to much lower detection limits

The set-up Rabbit-system with a flux of about 3E11 n/cm 2 s 1 mm of Cd leads to Cd ratio of about 20 to 30 for Al, Na, K, Mn, Cl Measurement of 40 % HPGe 127 I (n,) 128 I reaction resulting in a -peak at keV with a half-life of 24,99 m. Irradiation time: 5 m, counting time: 5 m, decay time: 3 m As standard I-solutions were used Samples: about 1 g Usually three sub samples taken because I is not distributed homogeneous (usually homogeneity higher than 10 %)

Radioprotection Due to the fact that the Cd-capsules are dismantled and re-used and, if a lot of samples have to be measured, the activity in the Cd increases, the dose to the NAA-operator increases Working a whole morning (dismantling is performed behind a lead window) leads to a H p (10) of about 3 Sv, whereas otherwise it is about 1 Sv

Excellent validation parameters No significant bias Good R w (r even at about 1 %) Specificity: the peak has some interference with the 23 Na(n,p) 23 Ne reaction, with a half-life of 37 s (so td > 3 m) MDA: for several matrices ranging from 50 ng/g up to 100 ng/g

Measurement uncertainty The K 0 -software is used to correct for sample filling height, sample density, matrix, measurement position The largest contributions to uncertainty are the reproducibility and the counting statistics. As reproducibility is at a level of 2,5 % we can say that for reasonable counting statistics (levels of about 10 ppm) the expanded uncertainty U is at a level of 6 %, at about 0.5 ppm U is about 10 %

What are the Iodine levels in Iodine rich foods? Some manufactures claim Iodine levels: are they correct?

Values differ in some cases from manufacturer specs The daily I intake mostly comes from the consumption of bread and fish, adding salt during cooking and drinking of milk.

1600 % 414 % 200 % 80 % Eating less bread might not be the solution (for I anyway)

Conclusion As INAA has to find “niche” markets to survive it has to focus on the validation of the chemical methods or to substitute where they fail (mostly sample preparation) EINAA is an excellent technique for the determination of I, for which our federal food safety agency has now officially recognised only EINAA Manufacturers are not always right when they label their products, is there a market for this?