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Modified micellar electrokinetic chromatography in the analysis of catechins and xanthines in chocolate
Author(s) -
Gotti Roberto,
Fiori Jessica,
Mancini Francesca,
Cavrini Vanni
Publication year - 2004
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.200406056
Subject(s) - micellar electrokinetic chromatography , theobromine , chemistry , chromatography , caffeine , sodium dodecyl sulfate , catechin , micelle , capillary electrophoresis , polyphenol , organic chemistry , aqueous solution , antioxidant , medicine , endocrinology
Modified micellar electrokinetic chromatography (MEKC) analysis of monomeric flavanols (catechin and epicatechin) and methylxanthines (caffeine and theobromine) in chocolate and cocoa was performed by using sodium dodecyl sulfate (SDS) as a principal component of the running buffer. Because of the reported poor stability of catechins in alkaline solutions, acidic conditions (pH 2.5) were chosen and consequently the electroosmotic flow (EOF) was significantly suppressed; this resulted in a fast anodic migration of the analytes partitioned into the SDS micelles. Under these conditions, variations of either pH value in acidic range or SDS concentration, showed to be not suitable to modulate the selectivity. To overcome this limit, use of additives to the SDS‐based running buffer was successfully applied and three different systems were optimized for the separation of (+)‐catechin, (−)‐epicatechin, caffeine, and theobromine in chocolate and cocoa powder samples. In particular, two mixed micelle systems were applied; the first consisted of a mixture of SDS and 3‐[(3‐cholamidopropyl)dimethylammonio]‐1‐propansulfonate (CHAPS) with a composition of 90 m M and 10 m M , respectively; the second was SDS and taurodeoxycholic acid sodium salt (TDC) with a composition of 70 m M and 30 m M , respectively. A further MEKC approach was developed by addition of 10 m M hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) to the SDS solution (90 m M ); it provided a useful cyclodextrin(CD)‐modified MEKC. By applying the optimized conditions, different separation profiles of the flavanols and methylxanthines were obtained showing interesting potential of these combined systems; their integrated application showed to be useful for the identification of the low level of (+)‐catechin in certain real samples. The CD‐MEKC approach was validated and applied to the determination of catechins and methylxanthines in aqueous extracts from four different commercial chocolate types (black and milk) and two cocoa powders.