1 Institute for Analytical Chemistry, Bio- and Chemosensors, University Regensburg, Universitätsstraße 31, 93053, Regensburg, Germany. antje.baeumner@ur.de.
2 Office of Dietary Supplements, National Institutes of Health, Bethesda, MD, 20817, USA. stephen.wise@nih.gov.
3 Scientist Emeritus, National Institute of Standards and Technology (NIST), Gaithersburg, MD, 20899, USA. stephen.wise@nih.gov.