production and validation of an alkaline phosphatase reference material in lyophilized milk

The paper describes the characterization and evaluation of a reference material in lyophilized milk to be used for the determination of alkaline phosphatase with the reference method iso 11816-1:2013. the reference material was produced at three levels of activity, calibrated for the determination of alkaline phosphatase activity in pasteurized (sample “60”), thermized (sample “600”), and raw milk (sample “6000”). the first assignment of the title and the uncertainties were realized through a round of 18 italian laboratories and the eur-mmp in 2014. in 2015, a second round was repeated with the participation of 17 expert laboratories of the net of nrls-mmp. the first titles were confirmed, whereas the second trial succeeded in a good improvement of the final uncertainties (sample “60” = 96.10 ± 2.03; sample “600” = 775.91 ± 13.03; sample “6000” = 6040.65 ± 126.89 mu/l). the materials were fully characterized according to iso guide 35:2006 and proved to be highly crono and temperature stable, so these are excellent candidates to be used for internal instrumental quality control or for the organization of interlaboratory trials for alkaline phosphatase determination in milk.