External standards of caffeic acid, neochlorogenic acid, catechin, procyanidin B2, quercetin-3-galactoside, m-coumaric acid, p-coumaric acid, and quercitrin (quercetin 3-rhamnoside) were purchased from Sigma- Aldrich, Inc. (St. Louis, MO, USA). Chlorogenic acid was purchased from MP medicals, France, and kaempferol-3-glucoside was obtained from the HWI group (Rheinzaberner, Germany). Analytical grade methanol, sodium fluoride (NaF), and formic acid (> 95%) were purchased from Merck® (Bengaluru, India). HPLC-grade water was obtained from a Milli-Q System with a resistivity of 18.2 mΩ (Millipore, Billerica, MA, USA).
Calibration standards were prepared by an appropriate dilution of stock solutions with 50% methanol. Nine different concentrations of each compound within 0.01—200 µg/mL for all the compounds were prepared to generate calibration curves. Standard curves were generated using linear regression (R2 of each standard curve was > 0.99).
Calibration standards were prepared by an appropriate dilution of stock solutions with 50% methanol. Nine different concentrations of each compound within 0.01—200 µg/mL for all the compounds were prepared to generate calibration curves. Standard curves were generated using linear regression (R2 of each standard curve was > 0.99).
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