Longitudinal On-Column Thermal Modulation for Comprehensive Two-Dimensional Liquid Chromatography

Abstract

Longitudinal on-column thermal modulation for comprehensive two-dimensional liquid chromatography is introduced. Modulation optimization involved a systematic investigation of heat transfer, analyte retention, and migration velocity at a range of temperatures. Longitudinal on-column thermal modulation was realized using a set of alkylphenones and compared to a conventional valve-modulator employing sample loops. The thermal modulator showed a reduced modulation-induced pressure impact than valve modulation, resulting in reduced baseline perturbation by a factor of 6; yielding a 6-14-fold improvement in signal-to-noise. A red wine sample was analyzed to demonstrate the potential of the longitudinal on-column thermal modulator for separation of a complex sample. Discrete peaks in the second dimension using the thermal modulator were 30-55% narrower than with the valve modulator. The results shown herein demonstrate the benefits of an active focusing modulator, such as reduced detection limits and increased total peak capacity.

Enhancing the Possibilities of Comprehensive Two-Dimensional Liquid Chromatography through Hyphenation of Purely Aqueous Temperature-Responsive and Reversed-Phase Liquid Chromatography

“…Only a few combinations are exempt from these modulation constraints as they offer inherent on-column refocusing, for example ion exchange x RP chromatography or aqueous size exclusion x RP chromatography. 13,14 To overcome these issues, several alternative modulation interfaces have been developed to promote refocusing of the analytes at the start of the 2 D column, 15 including: [1] dilution of the 1 D eluent with a weak solvent, making it more compatible with the 2 D stationary phase [16][17][18] , [2] splitting the 1 D flow, 19,20 [3] active modulation, in which trapping columns are used to refocus the analytes to remove of the bulk of the 1 D eluent, 16,21,22 [4] temperature modulation, which uses cold temperatures to trap the analytes, [23][24][25][26] [5] partial evaporation, which removes part of the fraction volume by selective evaporation of the mobile phase, 27,28 and [6] solvent switching, whereby the analytes are transferred from the 1 D mobile phase into a more compatible mobile phase. 29 Each of these approaches provide an adequate solution to particular combinations of separation modes, yet all of them come with certain penalties, including potential loss of D separation time or extreme instrumental complexity.…”

Focusing and non-focusing modulation strategies for the improvement of on-line two-dimensional hydrophilic interaction chromatography × reversed phase profiling of complex food samples

“…To partially alleviate these problems, different modulators have been designed; among them, thermal modulators are included. Within this group, several improvements have been presented, such as a vacuum-assisted evaporation interface aimed to remove the solvent from the 1 D effluent prior transfer to the 2 D [8], or the development of an oncolumn thermal modulation device [9]. This latter device was shown to be able to apply heating and cooling cycles to capture and elute analytes to the 2 D producing narrower bands.…”

Recent Developments in Two-Dimensional Liquid Chromatography: Fundamental Improvements for Practical Applications

“…Recent examples are evaporative membrane modulation 50 and longitudinal on-column thermal modulation. 51 A completely different approach that was recently proposed is fractionized stacking and sampling, where the 1 D effluent is split in a number of segments prior to introduction to the second-dimension column. 52 The last approach that we will discuss is vacuum-evaporation modulation (VEM), which was developed by the group of Guan.…”