The difference in color of the Sera-Mag Magnetic Carboxylate-Modified microparti

The phenomenon you are witnessing is the oxidation of the magnetite. The paramagnetic material used in our magnetic particles is a combination of magnetite (Fe3O4) and maghemite (Fe2O3). The magnetite can be converted to maghemite with oxidation over time, accelerated by elevated temperature. However, the oxidation state of the paramagnetic material does not impact magnetic response or binding performance or any aspect of the magnetic particle performance. Magnetite is a brownish black color and maghemite is light brown and this is the color change you have noticed with the lots in question. The oxidation of the magnetic material and consequently the related color change is not uncommon although the observation of the color change has been a rare occurrence over the tenure of the product. This aspect of the particles is not part of our release criteria nor is it part of your specification.