Among the heavy metals, there are some that are used in manufacturing and refining processes due to their positive properties. Nickel, for example, is an important alloying metal that is mainly used for steel refinement. Many consumer goods for daily use made of metal are coated with a nickel alloy (sewing needles, for example).
Nickel is one of the elements that cause particularly frequent allergic reactions due to its skin-sensitising properties. With prolonged skin contact, especially when sweat or other liquids are involved, nickel can slowly be extracted from the alloy. This dissolved nickel can then cause an allergy. Due to the extensive use of metal objects (containing nickel) in everyday use, a nickel allergy can cause severe adverse effects.
Since the use of nickel is irreplaceable in many areas to create certain material properties, it is not possible to do without nickel completely. In bound form within consumer goods, nickel cannot cause allergies. When testing for nickel, therefore, it is not the total content that is measured, but the so-called laxity. This means that it is measured how much nickel per surface can be dissolved by a sweat-like solution within a week (µg/cm2/week). In the case of utility and coated objects (also metal coatings), it is customary to carry out a so-called abrasion procedure before the laxity test. In this process, the metal test sample is constantly moved in a granular, defined abrasion medium so that the medium stresses the surface. This allows the surface to be artificially aged and a measurement is more likely to reflect how much nickel is released during use.
When measuring nickel release, the metal sample is first prepared and then immersed in an artificial sweat solution for a week. The concentration of nickel in the solution is then measured using ICP-OES. The nickel release can be determined after conversion to the surface of the metal part.