The case study samples were collected as individual 24h pool from four volunteers at three different time points. The three days were: after a polyphenol washout, after consuming a high polyphenol smoothie in the morning, and after a day following a high polyphenol diet, as described in Oesterle et al. The pooled human serum and Li-heparin plasma used for the LOD value comparison are listed in Table . The urine used for the matrix matched calibration curve and LOD comparison was an artificially made 24-h urine acquired from a female volunteer after following a low polyphenol diet for two days. The University of Vienna ethics committee, under authorization number #00650, approved the collection and measurement of samples from the participants following receiving their signed consent.