Review of recent insights in the measurement and modelling of the B-term dispersion and related mass transfer properties in liquid chromatography.

In this contribution, we review the recent literature relating to the measurement and modelling of all diffusion-dominated processes contributing to the efficiency of a chromatographic column. In first instance, this involves the measurement and modelling of the overall effective diffusion coefficient D (determining the so-called B-term band broadening). The latter manifests itself most clearly during a so-called peak parking experiment.

Detailed computational fluid dynamics study of the parameters contributing to the viscous heating band broadening in liquid chromatography at pressures up to 2500 bar in 2.1 mm columns.

Over the past years viscous heating band broadening occurring in high pressure liquid chromatography has been studied extensively. In the present numerical study, we investigate the fine details of this band broadening contribution under extreme high-pressure conditions (2500 bar). To analyze the results, we first show that viscous heating leads to two clearly distinguishable band broadening effects, one originating from the radial differences in the species migration velocity and the other from the axial variations.

Computational fluid dynamics study of potential solutions to alleviate viscous heating band broadening in 2.1 millimeter liquid chromatography columns.

We report on a numerical simulation study of a number of potential column technology solutions to minimize the plate height contribution (H) originating from the use of ultra-high pressures and their concomitant viscous heating effect. Looking as far as possible into the future of UHPLC, all main results are obtained for the case of a 2500 bar pressure gradient. However, to generalize the result, a correlation is given that can be used to interpolate the results to lower pressures with some 10% accuracy.

An explicit expression for the retention factor and velocity dependency of the mobile zone mass transfer band broadening in packed spheres beds used in liquid chromatography.

The present study proposes a ready-to-use analytical expression to calculate the mobile zone mass transfer contribution (h) in packed bed columns. For this purpose, first high-accuracy computations of the band broadening in a perfectly ordered sphere array (fcc-arrangement, external porosity ε=0.40) were made using computational fluid dynamics (CFD), covering a broad range of zone retention factors (2≤k''≤18) and reduced velocities (0≤ν≤48).

The stability of blood eosinophils in stable chronic obstructive pulmonary disease: a retrospective study in Belgian primary care.

Background: Blood eosinophil counts (BEC) were recently included in the 2019 Global Initiative for Obstructive Lung Disease (GOLD) guideline as an easily accessible theragnostic biomarker for Chronic Obstructive Pulmonary Disease (COPD). However, the stability of BEC remains insufficiently studied.

Methods: We conducted a retrospective study in six primary care practices in Belgium on data from Electronic Health Records of stable COPD patients, to characterise the stability of blood eosinophils over time.

The checkerboard model for the eddy-dispersion in laminar flows through porous media. Part I: Theory and velocity field properties.

The additivity assumption underlying Giddings' coupling model for the eddy-dispersion in laminar flows through heterogeneous media is critically analyzed and a potential solution for its non-additivity in the high velocity limit is presented. Whereas the unit cell in Giddings' model only consists of a single velocity bias step, the unit dispersion cell of the newly proposed model comprises two consecutive velocity bias steps. Consequently, the unit cell of this new model allows to account for the occurrence of an internal velocity bias rectification at high reduced velocities and is therefore additive in both the low and high velocity limit.

The checkerboard model for the Eddy-dispersion in Laminar flows through porous media. Part II: Application to ordered and disordered 2-D flow systems.

We report on a series of high-accuracy computational fluid dynamics band broadening simulations in three different 2-D flow systems: a 2-D pillar array and 2-D lumped packed bed geometries with different checkerboard velocity bias patterns. These media display a local maximum in the relationship between the eddy-dispersion plate height and the mobile phase velocity. The occurrence of such a dispersion maximum has not been reported before but appears to be a characteristic of regular chromatographic media with alternating velocity bias, at least in 2-D geometries.

A multiscale modelling study on the sense and nonsense of thermal conductivity enhancement of liquid chromatography packings and other potential solutions for viscous heating effects.

We report on a numerical study of the thermal conductivity and temperature distribution in analytical packed bed and monolithic HPLC columns to assess the feasibility of a number of potential solutions to the viscous heating problem that would normally impede high efficiency separations when moving to extreme operating pressures (e.g., 2500 bar).

A Training Game for Students Considering Family Medicine: an Educational Project Report.

The Groningen Institute Model for Management in Care Services aims to prepare medical students for their complex tasks as family physicians, based on the CanMEDS framework. Although initially developed for pharmacy students, the present paper reports on the eight-year experience with GIMMICS for family physician students at the Vrije Universiteit Brussel. The Groningen Institute Model for Management in Care Services is a training game that simulates real-life situations in a structured and supervised setting.

Optimizing design and employing permeability differences to achieve flow confinement in devices for spatial multidimensional liquid chromatography.

In spatial multi-dimensional liquid chromatography (LC) devices the flow of each dimension has to remain in the corresponding region, otherwise the separation efficiency is undermined. Adequate flow-confinement measures are necessary. Here, the use of permeability differences across different compartments of spatial two-dimensional (2D) and three-dimensional (3D) LC devices as a method to guide fluid flow and reduce analyte loss during the first, second- and third-dimension development was investigated with computational fluid dynamics (CFD) simulations.

Experimental and numerical study of band-broadening effects associated with analyte transfer in microfluidic devices for spatial two-dimensional liquid chromatography created by additive manufacturing.

Conventional one-dimensional column-based liquid chromatographic (LC) systems do not offer sufficient separation power for the analysis of complex mixtures. Column-based comprehensive two-dimensional liquid chromatography offers a higher separation power, yet suffers from instrumental complexity and long analysis times. Spatial two-dimensional liquid chromatography can be considered as an alternative to column-based approaches.

Two-dimensional insertable separation tool (TWIST) for flow confinement in spatial separations.

Spatial comprehensive two-dimensional liquid chromatography (LC×LC) may be an efficient approach to achieve high peak capacities in relatively short analysis times, thanks to parallel second-dimension separations [1,2]. A key issue to reach the potential of LC×LC is to achieve adequate flow control and confinement of the analytes to the desired regions, i.e.

Numerical and analytical investigation of the possibilities to enhance the thermal conductivity of core-shell particle packed beds.

We report on a numerical study of the thermal conductivity of core-shell particle packed bed columns. Covering a variety of packing structures and a broad range of mobile phase and porous zone conductivities, it was in all cases found that switching to particles with a highly conducting core (e.g.

Numerical investigation of band spreading generated by flow-through needle and fixed loop sample injectors.

The present study reports on a computational fluid dynamics study of the band broadening occurring in injector systems frequently used in contemporary liquid chromatography instruments. The aim of this work is to determine band broadening originating purely from the injection volume in absence of any other possible contribution (e.g.

A microfluidic distributor combining minimal volume, minimal dispersion and minimal sensitivity to clogging.

A new type of microfluidic flow distributor (referred to as the mixed mode or MM-distributor) is proposed. Its performance characteristics are determined using computational fluid dynamics (CFD), both in the absence and the presence of clogging, which is an important problem in microfluidic systems. A comparison is made with two existing, well-performing distributor types: the bifurcating (BF) distributor and an optimized diverging distributor, the so-called radially interconnected (RI) distributor.

A theoretical study on the advantage of core-shell particles with radially-oriented mesopores.

We report on a first-principles numerical study explaining the potential advantage of core-shell particles with strictly radially-oriented mesopores. Comparing the efficiency of these particles with fully porous and core-shell particles with a conventional (i.e.

Impact of thyroid autoimmunity on cumulative delivery rates in in vitro fertilization/intracytoplasmic sperm injection patients.

Objective: To predict the impact of thyroid autoimmunity (TAI) on the probability of delivery after a defined number of treatment cycles, using analysis of cumulative delivery rates in patients with and without TAI.

Design: Retrospective cohort study performed at the Center for Reproductive Medicine and Department of Endocrinology, University Hospital of Brussels, approved by the institutional review board of the hospital.

Setting: University hospital.

Design and evaluation of microfluidic devices for two-dimensional spatial separations.

Various designs of chips for comprehensive two-dimensional spatial liquid chromatography were investigated. The performance of these chips was initially evaluated using computational fluid dynamics (CFD). A bifurcating distributor with an angle of 140° between branches was implemented in order to achieve a homogeneous velocity field.

The impact of flow distribution on column performance: a computational fluid dynamics study.

In this manuscript, the band broadening contribution of a generic flow distributor and collector has been calculated using computational fluid dynamics (CFD). The effects of distributor design and operating conditions on distributor performance have been studied. The non uniform flow fields in the distributor cause band deformation and an increase in volumetric band variance (σv(2)).

Theoretical study on the impact of slip flow on chromatographic performance.

We used numerical simulations to investigate the recent observation that slip flow chromatography can obtain reduced plate heights as low as 0.032. The simulations were carried out for a 2D pillar array and a 3D face centred cubic particle stacking.

Experimental and numerical validation of the effective medium theory for the B-term band broadening in 1st and 2nd generation monolithic silica columns.

Effective medium theory (EMT) expressions for the B-term band broadening in monolithic silica columns are presented at the whole-column as well as at the mesoporous skeleton level. Given the bi-continuous nature of the monolithic medium, regular as well as inverse formulations of the EMT-expressions have been established. The established expressions were validated by applying them to a set of experimental effective diffusion (Deff)-data obtained via peak parking on a number of 1st and 2nd generation monolithic silica columns, as well as to a set of numerical diffusion simulations in a simplified monolithic column representation (tetrahedral skeleton model) with different external porosities and internal diffusion coefficients.

In situ measurement of the transversal dispersion in ordered and disordered two-dimensional pillar beds for liquid chromatography.

Using a fully transparent micropillar array chip and an optical "injection" setup capable of writing pulsed and continuous patterns into the flow by uncaging a fluorescent dye, highly detailed measurements of the transversal dispersion process in two-dimensional (2D) chromatographic beds could be made. With the use of water-glycerol mobile phase spanning a wide range of viscosities, the obtained data cover a broad range of reduced velocities (0 < ν < 3000) and show a clear leveling-off of the transversal dispersion coefficient at large reduced velocities. With dependence on the packing density, this leveling-off occurs at a value of about Dtrans/Dmol = 10 (ε = 0.

Detailed characterization of the kinetic performance of first and second generation silica monolithic columns for reversed-phase chromatography separations.

The kinetic performance of commercially available first generation and prototype second generation silica monoliths has been investigated for 2.0mm and 3.0-3.