Purelab ultra water system

High-performance liquid chromatography grade methanol, formic acid, trifluoroacetic acid (TFA), and acetonitrile were purchased from Fisher Scientific (Fair Lawn, NJ). Quercetin 3-glucoside (Qu3g), myricetin, kaempferol 3-glucorhamnoside, apigenin, and two cyanidin derivatives standards, cyanidin 3-glucoside (Cy3g), and cyanidin 3-rutinoside (Cy3r) were purchased from Sigma-Aldrich (St. Louis, MO). Kaempferol (Km), quercetin (Qu), and rutin (Rt) were purchased from Solarbio (Solarbio, China). Ultrapure water from PureLab Ultra Water System (ELGA LabWater, United Kingdom) was used in this experiment. All other reagents used were of analytical grade.

The aromatic amines used (Table 1) were purchased from Sigma-Aldrich (Steinheim, Germany), except for 4-chloro-2-methylaniline and 3-chloro-2,6-dimethylaniline which were purchased from Fluka (Darmstadt, Germany) and Alfa Aesar (Karlsruhe, Germany), respectively.Table 1

List of aromatic amines used with their corresponding abbreviation, structure, CAS-number, pKa value of the corresponding anilinium ion, log P value for the neutral compound, and purity

For the LPME optimization, the solvents dodecyl acetate (97%, abbreviated DDA), undecane (≥ 99%, UD), and dihexylether (97%, DHE) were purchased from Sigma-Aldrich, and 2-octanone (98%, 2O) was purchased from Alfa Aesar. Concentrated hydrochloric acid (ACS reagent, 37%, HCl) and sodium hydroxide (98%, NaOH) were purchased from Bernd Kraft (Duisburg, Germany).
During the derivatization, hydriodic acid (ACS reagent, unstabilized, 55%), sodium nitrite (99%), and Alizarin red S (98%) obtained from Sigma-Aldrich, and sodium sulfite (puriss. p.a., ACS reagent, RT, ≥ 98%) and sulfamic acid (T, ≥ 99%) from Fluka were used.
Diethyl ether (DEE) and HPLC grade methanol were purchased from Fisher Scientific (Schwerte, Germany), and ultrapure water was obtained from a PureLab Ultra water system from ELGA LabWater (Celle, Germany).