Research topics

The research in the Separation Science Group is driven by the overwhelming complexity experienced in especially natural but also in synthetic mixtures. Chromatography or electrophoresis is essential for qualitative and quantitative analysis of organic and inorganic molecules. After 100 year of development much open question remain and novel challenges continuously appear as users in all fields of chemistry and well beyond are confronted with new problems which can often only be addressed providing effective separation can be achieved. As progress is made new physical barriers are encountered which need be overcome. Research projects in the separation science group can roughly be grouped in two research types:

  1. The development of novel column chemistry, sample preparation or system technology to overcome contemporary limitations of chromatography, electrophoresis or organic mass spectrometry. This typically requires synthetic chemistry of organic, inorganic or polymeric nature.
  2. High- end implementation of state-of-the-art instrumentation to address problems in quantitative or qualitative analysis of organic molecules in complex mixtures in a targeted or untargeted way.

The current research projects are demonstrated below. Bachelor students can find the available interesting Master dissertation topics here.


Use of biopartitioning chromatography as a high throughput surrogate measure for brain penetration

The ability to permeate across the blood-brain barrier (BBB) is essential for drugs acting on the central nervous system (CNS). Biopartitioning chromatography can be used as an in vitro system to model the biopartitioning process of drugs when there are no active processes. The technique uses micellar mobile phases at physiological conditions and reversed phase columns to determine retention times (retention factors). The retention factor of a drug, which is influenced by the adsorption of surfactant monolayer to the stationary phase and by micelles present in the mobile phase, gives an indication of the drug penetration across a membrane.

The target of this project is to obtain an in vitro biopartitioning chromatography experiment that can correlate the retention factors with measured BBB penetration as good as possible.


Development of new stationary phases for stir bar sorptive extraction

Commercially available stir bars are coated with polydimethylsiloxane (PDMS). This polymer can extract apolar en semi-polar molecules, but is not suitable for the extraction of polar solutes. A lot of research have been done towards new coatings which are more suitable for the extraction of polar molecules. Until now, coatings are available, but none of them is thermally stable enough to be coupled to thermal desorption-gas chromatography.

In this research, new polymers with polar properties, which are thermally stable to 400°C or more, are synthesized and tested for the extraction of polar compounds in various samples.


Application of comprehensive two-dimensional HPLC in separation of copolymers

Knowledge of the exact composition and purity of advanced copolymers is of utmost importance given their influence on the final physical properties. The development of analytical techniques to examine these impurities is therefore crucial with respect of large industrial productions. A comprehensive two-dimensional HPLC separation technique with a slow size exclusion (SEC) separation in the first dimension and a fast reversed phase liquid chromatography (RPLC) separation in the second dimension was therefore developed and will be further elaborated to improve and optimise it's overall peak capacity. Separation methods for a range of different copolymer types will be developed as an asset for the polymer chemist.


RP-LC-ESI-MS/MS analysis of cyclic nucleotides in blood samples, animal tissue samples and plant extracts

3',5'-cyclic guanosine monophosphate (cGMP) and 3',5'-cyclic adenosine monophosphate (cAMP) are essential second messenger molecules. A quantitative solid phase extraction method (SPE) based on hydrophilic interaction on silica was developed and applied to blood samples, animal tissue samples and plant extracts. The stable isotope-labeled internal standards 2D115N3-cGMP and 13C10,15N5-cAMP were added prior to the sample preparation to ensure high precision and accuracy.

The samples were analyzed by reversed-phase liquid chromatography (RP-LC) coupled to negative electrospray (ESI)-MS/MS to selectively monitor several transitions of each metabolite. Basal plasma concentrations for fifteen healthy human patients were determined with this method as well as animal- and plant extracts concentrations. 2',3'-isomers of these cyclic nucleotides were detected and quantified in animal tissues and plant extracts. ELISA analysis was also performed for comparison of the results.


New strategy for fast chiral screening by high-performance liquid chromatography coupled with multivariate curve resolution-alternating least squares

A strategy aimed at developing rapid chiral screening technology was proposed in this paper with compressed screening time by mixing samples and screening the mixture of racemates. The data matrix of the mixture obtained by diode array detector or mass spectrometry was deconvoluted into resolved chromatograms and spectra by the multivariate curve resolution - alternating least squares algorithm. The individual racemate was then identified by the resolved spectra and its enantioselectivity was evaluated by the resolved chromatograms. Two example experiments were carried out to verify the feasibility of the strategy.
A mixture consisting 5 racemates was successfully screened on Chiralcel OD column in one fifth of the conventional analysis time. Another mixture made by 10 racemates gained nine tenth of the original screening time on three CSPs with an prediction accuracy above 90%.


Selectivity optimization with commercial coupled columns by gradient stationary phase optimized selectivity liquid chromatography

The gradient SOSLC protocol is successfully extended to coupled columns of 4 different stationary phases. Fast and full baseline separations of the mixture composed of 12 compounds of phenones, benzoic acids and benzoates are demonstrated within analysis time of 15 minutes under both isocratic and linear gradient conditions. Although the extra column void volume is increased by the use of tubings, the average relative deviation of prediction on selectivity factor results less than 2% and the maximum relative deviations are below 5%. These results indicate that the proposed gradient SOSLC protocol on coupled columns can also bring us robust and promising solution for separation of a given mixture.

The benefits of extending the gradient SOSLC to coupled column chromatography include wider commercial availability of stationary phases / columns, full use of the present columns in the lab, more selection of column coupler and flexible applications.


Enhanced fluidity liquid chromatography (EFLC) and supercritical fluid chromatography (SFC): greener alternatives to conventional HPLC

The mobile phase in SFC is the most influential parameter governing solute retention on the column. SFC mobile phases play an active- role in altering the distribution coefficient of the solute between the stationary phase and a compressed carrier fluid phase. SFC also differs from LC where solute retention is usually adjusted by changing either the chemical nature of the mobile or stationary phase within the column.

In this study SF-CO2 will be used as both SFC and Enhanced Fluid LC mobile phases to improve chromatographic advantages with parallel characterizations of several stationary phases to evaluate for environmental and pharmaceutical applications with UV, DAD, ELSD and TOF-MS detections.


Evaluation and optimization of Capillary ElectroChromatography as a high-efficient separation technique.

Capillary Electrochromatography (CEC) is theoretically a highly efficient technique but is not yet implemented in the industry as a standard separation technique.
This research is focused on the development of a neutral comparison tool for CEC capillaries in terms of speed and efficiency. The tool will be further used to address the problems in this electrodriven separation technique and to compare capillaries packed with the newest packing materials (sub-um, mixed mode, fused-core particles...) and new packing methods.