Retention and bandwidths prediction in fast gradient liquid chromatography. Part 2-Core-shell columns.

Recently, we confirmed that the well-established theory of gradient elution can be employed for prediction of retention in gradient elution from the isocratic data, method development and optimization in fast gradient chromatography employing short packed fully porous and monolithic columns and gradient times in between 1 and 2min, or even less. In the present work, we extended this study to short core-shell reversed-phase columns. We investigated the effects of the specification of the stationary phase in the core-shell structure on the prediction of gradient retention data.

Combined effects of mobile phase composition and temperature on the retention of phenolic antioxidants on an octylsilica polydentate column.

Combined effects of temperature and mobile-phase composition on retention and separation selectivity of phenolic acids and flavonoid compounds were studied in liquid chromatography on a polydentate Blaze C8 silica based column. The temperature effects on the retention can be described by van't Hoff equation. Good linearity of lnk versus 1/T graphs indicates that the retention is controlled by a single mechanism in the mobile phase and temperature range studied.

Possibilities of retention prediction in fast gradient liquid chromatography. Part 1: Comparison of separation on packed fully porous, nonporous and monolithic columns.

Due to ever increasing importance of short analysis times in modern HPLC practice, fast gradient elution is becoming widely used both in one-dimensional and two-dimensional separations, especially in the second dimension where the speed of separation is of primary importance. For method development and optimization, prediction of retention in gradient elution from the isocratic data is very important. This is principally possible using the well-established theory of gradient elution, especially for reversed-phase separations.

Optimization of comprehensive two-dimensional gradient chromatography coupling in-line hydrophilic interaction and reversed phase liquid chromatography.

In-line coupled comprehensive HILIC×RP systems should offer larger selectivity differences and better two-dimensional orthogonality than coupled RP×RP systems. However, this may not apply for all systems. The HILIC selectivity depends on the mix of selective polar and non-polar interactions with the functional groups, but also with the matrix of polar columns and depends on the sample type.

Combined effects of mobile phase composition and temperature on the retention of homologous and polar test compounds on polydentate C8 column.

Combined effects of temperature and mobile phase on the reversed phase chromatographic behavior of alkylbenzenes and simple substituted benzenes were investigated on a Blaze C8 polydentate silica-based column, showing improved resistance against hydrolytic breakdown at temperatures higher than 60 degrees C, in comparison to silica-based stationary phases with single attachment sites. For better insight into the retention mechanism on polydentate columns, we determined the enthalpy and entropy of the transfer of the test compounds from the mobile to the stationary phase. The enthalpic contribution dominated the retention at 80% or lower concentrations of methanol in the mobile phase.

Multidimensional LC x LC analysis of phenolic and flavone natural antioxidants with UV-electrochemical coulometric and MS detection.

A comprehensive 2-D LC x LC system was developed for the separation of phenolic and flavone antioxidants, using a PEG-silica column in the first dimension and a C(18) column with porous-shell particles or a monolithic column in the second dimension. Combination of PEG and C18 or C8 stationary phase chemistries provide low selectivity correlations between the first dimension and the second dimension separation systems. This was evidenced by large differences in structural contributions to the retention by -COOH, -OH and other substituents on the basic phenol or flavone structure.

Optimization of separation in two-dimensional high-performance liquid chromatography by adjusting phase system selectivity and using programmed elution techniques.

The overall peak capacity in comprehensive two-dimensional liquid chromatographic (LC x LC) separation can be considerably increased using efficient columns and carefully optimized mobile phases providing large differences in the retention mechanisms and separation selectivity between the first and the second dimension. Gradient-elution operation and fraction-transfer modulation by matching the retention and the elution strength of the mobile phases in the two dimensions are useful means to suppress the band broadening in the second dimension and to increase the number of sample compounds separated in LC x LC. Matching parallel gradients in the first and second dimension eliminate the necessity of second-dimension column re-equilibration after the independent gradient runs for each fraction, increase the use of the available second-dimension separation time and can significantly improve the regularity of the coverage of the available retention space in LC x LC separations, especially with the first- and second-dimension systems showing partial selectivity correlations.