Column selectivity for two‐dimensional liquid chromatography

Abstract

Selectivity of phase system is of primary concern when designing a 2-D separation, as it affects the 2-D system orthogonality and consequently the peak capacity controlling the number of peaks that can be separated in the available 2-D retention space limited by the time of analysis. Possibilities for characterization of LC phase system selectivity with respect to different polar and nonpolar structural units are compared, with special attention to multidimensional samples with various types of repeat groups, such as homopolymers, (co)polymers, fatty acid esters with various acyl lengths and number and position of double bonds, etc. Possibilities of the 2-D LC separations of these and other sample types, including pharmaceuticals, natural phenolic compounds, biopolymers, etc., using various combinations of separation modes are reviewed. Rules for design of comprehensive 2-D LC x LC systems are discussed, with respect to mobile phase compatibility in the two systems and modulation techniques suppressing band broadening connected with the sample fraction transfer from the first to the second dimension. Pitfalls connected with online connection of normal-phase and RP LC systems and their possible practical solutions are addressed and illustrated by practical examples.

Extraction, separation, and detection methods for phenolic acids and flavonoids

“…Two-dimensional LC enables improving the separation quality of various complex samples. In comparison to a single C 18 column, serially coupled PEG and C 18 columns show significant improvement in resolution of phenolic antioxidants in beer or wine samples [132,133]. Figure 5A illustrates the two-dimensional separation of standard phenolic compounds.…”

“…Two-dimensional PEG-C 18 RP6RP separation of (A) a mixture of phenolic standard solution and (B) of phenolics in concentrated beer sample [133].…”

Characterization of HPLC columns for two‐dimensional LC × LC separations of phenolic acids and flavonoids

“…Characterization of column selectivity is especially important in two-dimensional (2D) LC Â LC systems, employing a combination of two different columns with different separation modes in the first and in the second dimension to increase the number of separated compounds, that is, the peak capacity, n [16]. The multiplication effects of two-dimensional separation on the peak capacity are very strong, theoretically as high as the product of the peak capacities in the first and in the second dimension, n 2D ¼ n 1 Â n 2 , in so-called 'orthogonal' systems with completely different retention mechanisms controlling the selectivity [17].…”

Stationary phase characterization and method development

“…Jandera's efforts to understand column selectivity appear to be partially motivated by his interest in 2-D separations [121,122]. In ref.…”