liquid chromatography (HPLC) [14–17]. Only one method based on HPLC was developed for the simultaneous analysis B. M. Wagner: W. Windischhofer: H. J. Leis (*) Research Unit of Osteology and Analytical Mass Spectrometry, University Children’s Hospital, Medical University Graz, Auenbruggerplatz 30, 8036 Graz, Austria e-mail: hans.leis@medunigraz.at