Table 2.
Validation parameters obtained during in‐house validation
| substance | Retention time (min) | Linear range (ng/mL) | LOD (ng/mL) | LOQ (ng/mL) | RA (%) |
|---|---|---|---|---|---|
| Phloretin | 8.4 | 0.075‐10 | 0.075 | 0.25 | 49.6 ± 1.0 |
| 10–75 | |||||
| Epicatechin | 5.5 | 2.5–50 | 0.86 | 3.14 | 43.6 ± 2.5 |
| Procyanidin B1 | 4.2 | 1–50 | 0.19 | 0.75 | 40.8 ± 0.3 |
| Procyanidin B2 | 5.6 | 0.5–5 | 0.1 | 0.37 | 44.2 ± 3.1 |
| Procyanidin B5 | 6.5 | 1–50 | 0.44 | 1.61 | 42.3 ± 1.2 |
| Quercetin | 8.0 | 2.5–50 | 4.1 | 13.3 | 35.5 ± 5.1 |
Blank urine samples were spiked with analyte solutions and prepared as described in Section 2.1.1, resulting in a 1/10 dilution of the urine sample and analyzed by HPLC‐MS/MS. The data given in nanogram per milliliter are the concentration of the analytes in the diluted sample. LOD; LOQ; and
RA, apparent recovery were determined, all three were calculated according to the calibration method of the German Standard DIN 32635, as described before by Kleigrewe et al. 21.