Sample preparation
Mussel samples were triturated, homogenized and freeze-dried,
and were then kept in clean, dry containers. About 0.2 g of dry
and pulverized mussel sample was weighed in a Teflon bomb,
2 ml of concentrated nitric acid were added, and the bomb was
heated at 696 W for 2 min in the microwave oven. The bomb
was then cooled in a water-bath for 20 min, after which it was
opened carefully in a fume cupboard and the solution was
transferred into a 25 ml vessel. The pH was adjusted to 4.5 with
ammonia and the solution was diluted to 25 ml with ultrapure
water in a calibrated flask. Analytical blanks (2 ml of
concentrated nitric acid) were prepared in parallel in the same
way as the samples (adjusting the pH to 4.5 with ammonia
solution).