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

Abstract

The aim of the work is to contribute to rational selection of columns and mobile phases for 'orthogonal' twodimensional LC T LC operation of specific sample types, providing maximum increase in the peak capacity with respect to single-dimension HPLC. As a criterion of suitability, the dissimilarity of the separation selectivity of the phase separation systems was selected. For this purpose, correlations between the retention and molecular structure descriptors were used to characterize and compare the columns with respect to various types of selective interactions using the interaction indices as the general polarity scale characteristics and the linear free energy relationships (LFER) model employing selective molecular structural descriptors. Chemometric methods-cluster analysis using similarity dendrograms and multiple regression analysis-were used to classify several types of bonded C18, amide and polyethyleneglycol columns on the basis of differences in separation selectivities for selected phenolic and flavone standards. Systematic development of a comprehensive LC T LC method for two-dimensional separation of phenolic acids and flavone natural antioxidants was based on the selection of the combination of first-and second-dimension columns with low correlation of retention of representative standards providing a highly orthogonal two-dimensional separation system. The mobile phases providing best separation selectivity for phenolic compounds on each column tested were optimized using window-diagram optimization strategy. The final optimized conditions were employed for comprehensive LC T LC separations of natural antioxidants using a polyethylene glycol microcolumn in the first dimension and a short monolithic C18 column in the second dimension.

Comprehensive two‐dimensional liquid chromatography for polyphenol analysis in foodstuffs

“…As an interface for the automatic transfer of the 1 D effluent to the 2 D, many configurations have been proposed. The most widely used interface involves the use of two sampling loops with either a two‐position/ten‐port switching valve or two two‐position/six‐port switching valves as illustrated in Fig. .…”

“…RP‐LC × RP‐LC and HILIC × RP‐LC (with the exception of the RP‐LC × HILIC in ref. ) have been developed and successfully applied to the analysis of polyphenolic compounds in real‐world food samples . Only one application dealt with the use of SEC and RP‐LC for analysis of Camellia sinensis green and black teas .…”

“…The first LC × LC system was introduced by Erni and Frei for the analysis of a complex plant extract with a SEC column as the 1 D and an RP column as the 2 D, connecting the two columns with a two‐position eight‐port switching valve . Since then, a broad range of papers on LC × LC have been published, covering applications and theoretical considerations; some of them are specifically devoted to polyphenol analysis and roughly 87% come from five different research groups very active in the field . Additionally, some reviews covering both theoretical and practical aspects for such bioactive molecules have been reported .…”

Dual hydrophilic interaction‐RP retention mechanism on polar columns: Structural correlations and implementation for 2‐D separations on a single column

“…(3)). The molecular structural descriptors of the sample compounds [31] characterizing the size of sample molecules, V x , its polarity, p, and hydrogen bonding acidity, a, and basicity, b, are listed in Table 1. They were used to determine the HILIC and the RP system parameters m 0 , s 0 , a 0 and b 0 characterizing selective non-polar, dipole-dipole and hydrogen-bonding interactions.…”

Assessment of column selection systems using Partial Least Squares

“…Availability of more than 1000 commercial stationary phases [2,3], makes column selection a crucial process. Therefore, it is not surprising that numerous papers [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] describing various attempts to achieve this are being continuously published.…”