Micellar electrokinetic capillary chromatography of methylxanthines‐containing beverages: discussion of the molecular species involved

Abstract

Micellar electrokinetic capillary chromatography (MECC) experimental conditions were applied to 12 samples of methylxanthine-containing infusions of different commercial brands of yerba mate, coffee, tea and cocoa as well as two cola drinks. The best resolution in this mode of automated high-performance capillary electrophoresis (HPCE) was achieved here when using 15 kV voltage in an uncoated fused-silica capillary of 45 cm length (40 cm effective length), 50 mM sodium dodecylsulfate, 90 mM pH 8.5 borate buffer and UV detection. Theobromine, caffeine and theophylline were separated, and the peak splitting due to tautomeric species was observed. Experimental conditions were controlled, keeping constant the size of the elution window in each analysis. The limit of detection was less than 1 mg l −1 , the limit of quantitation was 2.5 mg l −1 and the work range was 2.5-300 mg l −1 . This HPCE-MECC system has proved suitable for the analysis/quality control of xanthines in beverages for consumption. Roles of various parameters as well as distinctly charged species of each xanthine and the origin of peak splitting in this MECC system are discussed.

Recent advances in the application of capillary electromigration methods for food analysis

“…On the other hand, the derivatization time had a negative effect while the concentration of SDS A MEKC-UV method was developed to detect and quantify the methylxanthines theobromine, caffeine and theophylline in commercial brands of yerba mate, coffee, tea and cocoa as well as two cola drinks [109]. The separation was carried out in an uncoated fused-silica capillary using a 90 mM borate buffer at pH 8.5 containing 50 mM SDS.…”

Detection of caffeine and its main metabolites for early diagnosis of Parkinson's disease using micellar electrokinetic capillary chromatography

“…In the preliminary experiment without using SDS, it was found that CA migrated with the EOF and was not well separated from the other compounds in the sample, though the three metabolites can be separated completely. To approach this problem, the long alkyl-chain anionic surfactant SDS, the most widely used surfactant, was chosen in the present study, due to its high aqueous solubility, small UV molar absorptivity even at low wavelengths, and availability [32].…”

“…At present, the most common methods for determining the plasma levels of CA and its metabolites are HPLC [15,[24][25][26], LC-MS [27][28][29], and CE [30][31][32][33][34]. The costs of performing LC-MS are high, which sometimes limits its application.…”

“…MEKC is a mode of automated CE, which offers a combination of unique features of CZE and RP-HPLC such as high efficiency, rapid analysis, and versatility of modifying chemical selectivity in the separation process [37]. MEKC has been applied to the separation of neutral, ionic compounds and so on [38,39], and previous studies have demonstrated its use for determining the levels of CA and its metabolites [30][31][32][33]40]. However, most of the measurements were performed on beverage [32], water [28], or urine samples [25], few were about the measurement of CA and its metabolites in human plasma/serum.…”

“…MEKC has been applied to the separation of neutral, ionic compounds and so on [38,39], and previous studies have demonstrated its use for determining the levels of CA and its metabolites [30][31][32][33]40]. However, most of the measurements were performed on beverage [32], water [28], or urine samples [25], few were about the measurement of CA and its metabolites in human plasma/serum. Moreover, some studies were mainly focused on CA, TP, and TB, but not PX [30,41], the primary metabolite of CA (Supporting Information Fig.…”