spiked with a solution of SEA(two levels, Table1) homogenised again by ultra-turraxing. the homogenised slurries were free-dried. the freeze-dried materials were then milled in a cryogenic mill. thereafter, the materials were sequentially diluted in three steps with blank powder, and after each dilution, materials were mixed in a three-dimensional mixer.
the materials were filled into plastic zip-lock bags by use of an automated filled machine, and one bag of each material was put in an alumina sachet for light and moisture protection. The sets were stored at -20c (current storage temperature of the candidate CRM until long-term stability data will be avaiable, which might allow shifting the batch to a higher storage temperature, e.g. 4c)