Fig. 1.

Study overview. a Preparation of the Quartet metabolite reference materials. Four B lymphoblastoid cell lines (LCLs) of a family quartet including the father (F7), mother (M8), and monozygotic twin daughters (D5 and D6) were used for extracting metabolites. Eleven spike-ins were added to the cell extract and aliquoted into 1000 tubes per sample. b Data generation. Targeted (T) and untargeted (U)-based metabolomic datasets were generated in different laboratories for inter-laboratory proficiency tests. Long-term monitoring was conducted using a targeted strategy within a laboratory (T-L4) for 2 years