Comprehensive two-dimensional liquid chromatography coupled to the ABTS radical scavenging assay: a powerful method for the analysis of phenolic antioxidants.

The on-line combination of comprehensive two-dimensional liquid chromatography (LC × LC) with the 2,2'-azino-bis(3-ethylbenzothiazoline)-6 sulphonic acid (ABTS) radical scavenging assay was investigated as a powerful method to determine the free radical scavenging activities of individual phenolics in natural products. The combination of hydrophilic interaction chromatography (HILIC) separation according to polarity and reversed-phase liquid chromatography (RP-LC) separation according to hydrophobicity is shown to provide much higher resolving power than one-dimensional separations, which, combined with on-line ABTS detection, allows the detailed characterisation of antioxidants in complex samples. Careful optimisation of the ABTS reaction conditions was required to maintain the chromatographic separation in the antioxidant detection process.

Toward unraveling grape tannin composition: application of online hydrophilic interaction chromatography × reversed-phase liquid chromatography-time-of-flight mass spectrometry for grape seed analysis.

Despite the significant importance of tannins in viticulture and enology, relatively little is known about the detailed chemical composition of these molecules. This is due to challenges associated with the accurate analytical determination of the highly structurally diverse proanthocyanidins which comprise tannins. In this contribution, we address this limitation by demonstrating how online comprehensive two-dimensional liquid chromatography (LC × LC) coupled to high resolution mass spectrometry (HR-MS) can be exploited as a powerful analytical approach for the detailed characterization of grape seed tannins.

Systematic optimisation and evaluation of on-line, off-line and stop-flow comprehensive hydrophilic interaction chromatography×reversed phase liquid chromatographic analysis of procyanidins. Part II: application to cocoa procyanidins.

Procyanidins present a severe analytical challenge due to their structural complexity and diversity. Comprehensive two-dimensional hydrophilic interaction chromatography×reversed-phase liquid chromatography (HILIC×RP-LC) provides a highly efficient separation system for procyanidins. In the first part of this contribution a systematic approach for the optimisation and evaluation of HILIC×RP-LC analyses in on-line, off-line and stop-flow modes was presented.

Systematic optimisation and evaluation of on-line, off-line and stop-flow comprehensive hydrophilic interaction chromatography×reversed phase liquid chromatographic analysis of procyanidins, part I: theoretical considerations.

Comprehensive two-dimensional liquid chromatography (LC×LC) provides significantly improved separation for complex real-life samples. LC×LC can be performed in one of three different ways, using on-line, off-line, or stop-flow configurations. We have previously shown how off-line comprehensive hydrophilic interaction chromatography (HILIC)×reversed-phase liquid chromatography (RP-LC) provides a powerful separation system for procyanidins (PCs), one of the most complex fractions of natural phenolics.

Comprehensive two-dimensional liquid chromatographic analysis of rooibos (Aspalathus linearis) phenolics.

Rooibos tea is an unique beverage prepared from unfermented and fermented plant material of the endemic Cape fynbos plant, Aspalathus linearis. The well-known health-promoting benefits of rooibos are partly attributed to its phenolic composition. Detailed investigation of the minor phenolic constituents of rooibos is, however, hampered by the limitations associated with conventional HPLC methods used for its analysis.

Kinetic optimisation of the reversed phase liquid chromatographic separation of proanthocyanidins on sub-2 μm and superficially porous phases.

Phenolic compounds, and proanthocyanidins in particular, are important natural molecules which are of significant importance due to their sensory and biological activities. The analysis of proanthocyanidins in natural products is very challenging due to their complex nature. In this study, the kinetic performance of a range of recently developed C18 columns, including sub-2 μm fully porous and 2.

Fast method development of rooibos tea phenolics using a variable column length strategy.

The development of a method for the separation of standard compounds of the 15 main phenolics found in rooibos tea is presented. The separation of these compounds in a single HPLC analysis is particularly challenging due to the similarity of rooibos phenolics. As a result, multiple methods are often required to analyze all major phenolics in rooibos tea samples.

Recent developments in the HPLC separation of phenolic compounds.

Phenolic compounds represent a class of highly complex naturally occurring molecules that possess a range of beneficial health properties. As a result, considerable attention has been devoted to the analysis of phenolics in a variety of samples. HPLC is the workhorse method for phenolic separation.

Off-line comprehensive two-dimensional hydrophilic interaction x reversed phase liquid chromatographic analysis of green tea phenolics.

The separation of green tea phenolic compounds by comprehensive 2-D LC (LCxLC) has been studied. An off-line LCxLC system was designed based on hydrophilic interaction chromatography in the first dimension and gradient RP-LC using a C18 column in the second dimension, to separate compounds based on polarity and hydrophobicity, respectively. Green tea was found to contain a complex composition of low molecular weight phenolic compounds, identified by fluorescence, diode-array and negative ESI-MS detection systems.

Off-line comprehensive 2-dimensional hydrophilic interaction x reversed phase liquid chromatography analysis of procyanidins.

The development of an off-line comprehensive 2-dimensional liquid chromatography (2-D-LC) method for the analysis of procyanidins is reported. In the first dimension, oligomeric procyanidins were separated according to molecular weight by hydrophilic interaction chromatography (HILIC), while reversed phase LC was employed in the second dimension to separate oligomers based on hydrophobicity. Fluorescence, UV and electrospray ionisation mass spectrometry (ESI-MS) were employed for identification purposes.