Highly-diverse compounds (n=105) were combined in a multianalyte solution and diluted to seven concentration levels in ACN/H2O (1:9 v/v). A mixture of labelled internal standards was used for sample preparation (Table ). The complete list of analytes and the corresponding concentration levels are summarized in the Supporting Information (Table ). Solvents for extraction and eluents were LC-MS grade. Water was supplied by VWR chemicals and methanol and ACN from Honeywell Riedel-del Haen. Ammonium fluoride (NH4F, EMSURE® ACS, Honeywell Fluka) was of high purity (> 98%).