Nonaqueous capillary electrophoretic separation of polyphenolic compounds in wine using coated capillaries at high pH in methanol

Abstract

Nonaqueous capillary electrophoretic separation of a group of flavonoids (quercetin, myricetin, catechin, epicatechin) and resveratrol in wine was investigated in methanol at high pH. Malonate background electrolyte (pH* 13.5, ionic strength I = 14.2 mmol/L) provided highly repeatable separations of the analytes. Tests of untreated and coated (poly(glycidylmethacrylate-co-N-vinylpyrrolidone)) capillaries showed the analysis to be faster (6.5 min vs. 25 min) and the repeatability better in the coated capillaries. The coating procedure was simple and highly repeatable and the coating was stable during 40-45 runs. Determination of the last migrating peaks (epicatechin, resveratrol and catechin) was achieved merely by evaporating the wine samples and reconstituting the residue in methanol. For determination of the first migrating peaks (quercetin and myricetin) the samples were submitted to solid-phase extraction in C8 cartridges.

Analysis of polyphenols using capillary zone electrophoresis – Determination of the most effective wine sample pre‐treatment method

“…(ii) 3 mL of wine sample was evaporated under nitrogen stream at 501C [23]. The residue was reconstituted in 3 mL of ethanol and filtered with a 0.45-mm syringe filter.…”

“…These advantageous properties of red wine have been attributed to polyphenols. For this reason, a lot of studies have been performed for the determination of polyphenols in wine samples by use of HPLC [7,8,22] and CE [16,17,[23][24][25][26]. In recent years, CE has been established as a versatile and robust tool for food analysis.…”

“…In addition, the primary goal is to optimize the sample preparation procedure in order to determine the one that is simple, fast and reliable. Therefore, three LLE-procedures [7,16,24], a SPEprocedure, a procedure that involves evaporation and reconstitution of wine sample [23] and a direct injection of wine sample after dilution and filtration [25] were compared and the most effective method was applied to Cypriot wines. To our knowledge, this is the first time that different wine sample pre-treatment methods are compared using CE.…”

Characterization of hydroxyaromatic compounds in vegetable oils by capillary electrophoresis with direct injection in an oil‐miscible KOH/propanol/methanol medium

“…For this purpose, PrOH and mixtures of PrOH with moderate amounts of MeOH, which are capable of supporting the direct injection of the vegetable oils in the capillary, were used. Attending to the acidic character of all primary alcohols when compared with water, and at the sight of the pK a * data of weak acids in MeOH [51,57], very high pH* values were expected to be necessary to ionise phenols in PrOH and MeOH/PrOH mixtures. Thus, the mixtures were made both conductive and strongly alkaline with KOH.…”

“…In comparison with the corresponding pK a values in water, the pK a * values of carboxylic acids and phenols increase up to 5 log units in MeOH [51,56]. Several polyphenols, including flavonoids and resveratrol, were separated in wine samples using malonic acid and tetrabutylammonium hydroxide in MeOH; the second ionisation constant of the diprotic acid was used to buffer the high pH* required [57].…”