Frédéric Lynen

Ghent University, Gand, Flemish, Belgium

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Publications (31)78.66 Total impact

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    ABSTRACT: In recent decades, several types of persistent substances are detected in the aquatic environment at very low concentrations. Unfortunately, conventional water treatment processes are not able to remove these micropollutants. As such, advanced treatment methods are required to meet both current and anticipated maximally allowed concentrations. Plasma discharge in contact with water is a promising new technology, since it produces a wide spectrum of oxidizing species. In this study, a new type of reactor is tested, in which decomposition by atmospheric pulsed direct barrier discharge (pDBD) plasma is combined with micropollutant adsorption on a nanofiber polyamide membrane. Atrazine is chosen as model micropollutant with an initial concentration of 30 μg/L. While the H2O2 and O3 production in the reactor is not influenced by the presence of the membrane, there is a significant increase in atrazine decomposition when the membrane is added. With membrane, 85% atrazine removal can be obtained in comparison to only 61% removal without membrane, at the same experimental parameters. The by-products of atrazine decomposition identified by HPLC-MS are deethylatrazine and ammelide. Formation of these by-products is more pronounced when the membrane is added. These results indicate the synergetic effect of plasma discharge and pollutant adsorption, which is attractive for future applications of water treatment. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Water Research 11/2014; DOI:10.1016/j.watres.2014.11.009 · 5.32 Impact Factor
  • Sander Delahaye, Frederic Lynen
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    ABSTRACT: The performance of stationary-phase optimized selectivity liquid chromatography (SOS-LC) for improved separation of complex mixtures has been demonstrated before. A dedicated kit containing column segments of different lengths and packed with different stationary phases is commercially available together with algorithms capable of predicting and ranking isocratic and gradient separations over vast amounts of possible column combinations. Implementation in chromatographic separations involving compressible fluids, as is the case in supercritical fluid chromatography, had thus far not been attempted. The challenge of this approach is the dependency of solute retention with the mobile-phase density, complicating linear extrapolation of retention over longer or shorter columns segments, as is the case in conventional SOS-LC. In this study, the possibilities of performing stationary-phase optimized selectivity supercritical fluid chromatography (SOS-SFC) are demonstrated with typical low density mobile phases (94% CO2). The procedure is optimized with the commercially available column kit and with the classical isocratic SOS-LC algorithm. SOS-SFC appears possible without any density correction, although optimal correspondence between prediction and experiment is obtained when isopycnic conditions are maintained. As also the influence of the segment order appears significantly less relevant than expected, the use of the approach in SFC appears as promising as is the case in HPLC. Next to the classical use of SOS for faster baseline separation of all solutes in a mixture, the benefits of the approach for predicting as wide as possible separation windows around to-be-purified solutes in semi-preparative SFC are illustrated, leading to significant production rate improvements in (semi-) preparative SFC.
    Analytical Chemistry 11/2014; DOI:10.1021/ac503313j · 5.83 Impact Factor
  • Piotr Álvarez Porebski, Frederic Lynen
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    ABSTRACT: Offline two dimensional liquid chromatography (LC) x capillary gel electrophoresis (CGE) and LC x (24) multiplexed-CGE methodologies were developed for the separation of oligonucleotides of therapeutic size. Both ion-pair chromatography (IPC) and ion-exchange chromatography (IEC) were studied as methods for the first dimension and single and multiplexed capillary electrophoresis methods in entangled polymer solutions were used for the second dimension separations. Electrokinetic and pressure injection were evaluated for the analysis of the collected LC fractions. The comprehensive separation was optimized with standard mixtures of poly adenosine, thymidine, cytosine and uracil homodeoxyoligonucleotides up to 35 bases long. Highly orthogonal methodologies and overall peak capacities of 6435 and 6993 for IPC x CGE and IEC x CGE, respectively, were obtained within a few hours analysis time.
    Journal of Chromatography A 04/2014; DOI:10.1016/j.chroma.2014.02.007 · 4.26 Impact Factor
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    ABSTRACT: Non-thermal plasma treatment by an electrical discharge generated above water was applied to study the destruction of anthraquinonic dye Acid Blue 25 in aqueous solutions. The direct current glow discharge above water sustaining in ambient air was used as a source of non-equilibrium plasma. The effect of operational parameters such as initial dye concentration, discharge current, pH and addition of salts on the substrate degradation was investigated. The highest G 50 value was obtained for 45 mA current at low solution conductivity and G50 value was about 2.4 g/kWh. The degradation efficiency of AB25 in distilled water was compared with those in complex matrices such as natural and sea waters. It is shown that the degradation in natural matrices is less effective due to presence of OH radicals scavengers like HCO3-. The intermediates of AB25 dye destruction were studied by means of HPLC with multi-wavelength detector and combination of HPLC with time-of-flight mass-spectroscopy.
    Journal of Advanced Oxidation Technologies 01/2014; 17(2). · 1.11 Impact Factor
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    ABSTRACT: Analysis of drugs and metabolites in biological matrices such as blood or plasma by LC-MS is routinely challenged by the presence of large quantities of competing molecules for ionization in soft ionization sources, such as proteins and phospholipids. While the former can easily be removed by protein precipitation, pre-analytical extraction of the latter is necessary because they show very high retention in reversed-phase LC resulting in long analysis times or in ion suppression effects when not eluted before the next runs. A novel HILIC-based SPE approach, making use of silica cartridges and of acetone as organic solvent, is introduced as a potent alternative to current commercial methods for phospholipid removal. The methodology was developed and tested for a broad polarity range of pharmaceutical solutes (log P from 0 to 6.6) and broad applicability can therefore be envisaged.
    Analytical and Bioanalytical Chemistry 08/2013; 406(2). DOI:10.1007/s00216-013-7281-7 · 3.58 Impact Factor
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    ABSTRACT: Here we report a metabolomics discovery study conducted on blood serum samples of patients in different stages of chronic kidney disease (CKD). Metabolites were monitored on a quality controlled holistic platform combining reversed-phase liquid chromatography coupled to high-resolution quadrupole time-of-flight mass spectrometry in both negative and positive ionization mode and gas chromatography coupled to quadrupole mass spectrometry. A substantial portion of the serum metabolome was thereby covered. Eighty-five metabolites were shown to evolve with CKD progression of which 43 metabolites were a confirmation of earlier reported uremic retention solutes and/or uremic toxins. Thirty-one unique metabolites were revealed which were increasing significantly throughout CKD progression, by a factor surpassing the level observed for creatinine, the currently used biomarker for kidney function. Additionally, 11 unique metabolites showed a decreasing trend.
    Metabolomics 06/2013; 10(3). DOI:10.1007/s11306-013-0592-z · 3.97 Impact Factor
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    ABSTRACT: Chronic kidney disease (CKD) is a devastating illness characterized by accumulation of uremic retention solutes in the body. The objective of this study was to develop and validate a simple, rapid, and robust UPLC-MS-MS method for simultaneous determination, in serum, of seven organic acid uremic retention toxins, namely uric acid (UA), hippuric acid (HA), indoxylsulfate (IS), p-cresylglucuronide (pCG), p-cresylsulfate (pCS), indole-3-acetic acid (IAA), and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF). Isotopically labeled internal standards (d(5)-HA; 1,3-(15)N(2)-UA, and d(5)-IAA) were used to correct for variations in sample preparation and system performance. Separation on a C18 column was followed by negative electrospray ionization and tandem mass spectrometric detection. Accuracy was below the 15 % threshold. Within-day precision varied from 0.60 to 4.54 % and between-day precision was below 13.33 % for all compounds. The applicability of the method was evaluated by analyzing 78 serum samples originating both from healthy controls and from patients at different stages of CKD. These results were compared with those obtained by use of conventional HPLC-PDA-FLD methods. A good correlation was obtained between both methods for all compounds.
    Analytical and Bioanalytical Chemistry 01/2013; 405(6). DOI:10.1007/s00216-012-6636-9 · 3.58 Impact Factor
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    ABSTRACT: A dioxomolybdenum(VI) complex has been covalently anchored onto mesoporous titania by a silicon-assisted transesterification route. The grafting of the complex to the mesoporous structure was confirmed by diffuse reflectance infrared Fourier transform, Raman and UV-Vis spectroscopy and by nitrogen sorption experiments. The ability of the grafted complex to activate molecular oxygen (O-2) has been evaluated in the photooxidation of diphenylmethane to produce benzophenone. The photooxidation of diphenylmethane was monitored continuously by in situ dispersive Raman spectroscopy. A scheme for the activation of molecular oxygen under very mild conditions is proposed. A comparison with the same complex anchored onto commercial titanium P-25 and silica gel revealed both the beneficial effect of the mesoporous structure and the existence of a synergistic effect between MoO/TiO2/O-2/light entities, which promotes the photooxidation process under green chemistry conditions. Finally, the heterogeneous catalyst is sustainable; it can be recycled and reused without significant loss in activity or selectivity.
    Transition Metal Chemistry 01/2013; 38(2-2):119-127. DOI:10.1007/s11243-012-9668-2 · 1.40 Impact Factor
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    ABSTRACT: The present contribution investigates the quantitation aspects of mass-sensitive detectors with nebulizing interface (ESI-MSD, ELSD, CAD) in the constant pressure gradient elution mode. In this operation mode, the pressure is controlled and maintained at a set value and the liquid flow rate will vary according to the inverse mobile phase viscosity. As the pressure is continuously kept at the allowable maximum during the entire gradient run, the average liquid flow rate is higher compared to that in the conventional constant flow rate operation mode, thus shortening the analysis time. The following three mass-sensitive detectors were investigated: mass spectrometry detector (MS), evaporative light scattering detector (ELSD) and charged aerosol detector (CAD) and a wide variety of samples (phenones, polyaromatic hydrocarbons, wine, cocoa butter) has been considered. It was found that the nebulizing efficiency of the LC-interfaces of the three detectors under consideration changes with the increasing liquid flow rate. For the MS, the increasing flow rate leads to a lower peak area whereas for the ELSD the peak area increases compared to the constant flow rate mode. The peak area obtained with a CAD is rather insensitive to the liquid flow rate. The reproducibility of the peak area remains similar in both modes, although variation in system permeability compromises the 'long-term' reproducibility. This problem can however be overcome by running a flow rate program with an optimized flow rate and composition profile obtained from the constant pressure mode. In this case, the quantification remains reproducibile, despite any occuring variations of the system permeability. Furthermore, the same fragmentation pattern (MS) has been found in the constant pressure mode compared to the customary constant flow rate mode.
    Journal of Chromatography A 12/2012; 1274. DOI:10.1016/j.chroma.2012.12.013 · 4.26 Impact Factor
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    ABSTRACT: IR and NMR spectroscopy were used to determine the silanol content in the most common mesoporous ordered silicas: MCM-41, MCM-48, SBA-15 and SBA-16. In addition, a spray dried MCM-41 and an ethene bridged PMO are investigated. The results are compared with a commercial chromatographic silica (Nucleosil). The complete distribution of surface and bulk silanols, and of isolated, geminal and vicinal silanols for all these materials is presented. A distinction is made between the total silanol number and the reachable or surface silanol content. The latter is determined by controlled reactions with simple silanes. All mesoporous ordered silicas, and especially the thick walled SBA-type materials and the PMO contain a surprisingly high amount of total silanol sites, albeit that up to 90% of these silanols are buried inside the walls and are not reachable for small silanes.
    Physical Chemistry Chemical Physics 11/2012; 15(2). DOI:10.1039/c2cp42811c · 4.20 Impact Factor
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    ABSTRACT: The identification and quantitation of a wide range of lipids in complex biological samples is the first step in lipidomic studies. High-performance liquid chromatography - mass spectrometry (HPLC/MS) coupling has the highest potential to obtain detailed information on the whole lipidome, but the reliable quantitation of multiple lipid classes is still a challenging task. In this work, we describe a new method for the non-targeted quantitation of polar lipid classes separated by hydrophilic interaction liquid chromatography (HILIC) followed by positive-ion electrospray ionization mass spectrometry (ESI-MS) detection using a single internal standard and response factor (RF) approach. The developed method enables the quantitation of lipid classes and lipid molecules inside these classes in contrast to the conventional targeted quantitation, which is based on pre-defined selected reaction monitoring (SRM) transitions for selected lipids only. In the non-targeted quantitation procedure described here, concentrations of lipid classes are obtained by the peak integration in the HILIC chromatograms multiplied by their RFs related to the single internal standard (sphingosyl PE, d17:1/12:0) common for all lipid classes. The accuracy, reproducibility and robustness of our method have been checked by various means: A/ the comparison with conventional lipidomic quantitation using SRM scans on the triple quadrupole (QqQ) mass analyzer, B/ 31P nuclear magnetic resonance (NMR) absolute quantitation of whole extract, C/ the method robustness have been verified by subsequent measurements of three different people, D/ the method transfer to different HPLC/MS system using different chromatographic conditions, E/ the comparison with previously published results for identical samples, especially human reference plasma from the National Institute of Standards and Technology (NIST plasma). This method has been applied to the analyses of human plasma, egg yolk and porcine liver extracts.
    Analytical Chemistry 10/2012; 84(22). DOI:10.1021/ac3024476 · 5.83 Impact Factor
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    ISCC 36; 05/2012
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    ABSTRACT: This contribution discusses the difference in chromatographic performance when switching from the customary employed constant flow rate gradient elution mode to the recently re-introduced constant pressure gradient elution mode. In this mode, the inlet pressure is maintained at a set value even when the mobile phase viscosity becomes lower than the maximum mobile phase viscosity encountered during the gradient program. This leads to a higher average flow rate compared to the constant flow rate mode and results in a shorter analysis time. When both modes carry out the same mobile phase gradient program in volumetric units, normally identical selectivities are obtained. However, small deviations in selectivity are found due to the differences in pressure and viscous heating effects. These selectivity differences are of the same type as those observed when switching from HPLC to UHPLC and are inevitable when speeding up the analysis by applying a higher pressure. It was also found that, when using concentration-sensitive detectors, the constant pressure elution mode leads to identical peak areas as the constant flow rate mode. Also the linearity is maintained. In addition, the repeatability of the peak area and retention time remains the same when switching between both elution modes.
    Journal of Chromatography A 10/2011; 1232:65-76. DOI:10.1016/j.chroma.2011.10.019 · 4.26 Impact Factor
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    6th International symposium on Nanoporous Materials (Nanoporous materials VI ; Nano-6); 08/2011
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    36th HPLC Symposium; 06/2011
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    ABSTRACT: The kinetic plot method, originally developed for isocratic separations, was extended to the practically much more relevant case of gradient elution separations. A set of explicit as well as implicit data transformation expressions has been established. These expressions can readily be implemented in any calculation spread-sheet program, and allow to directly turn any experimental data set representing the relation between the separation efficiency and the flow rate measured on a single column into the kinetic performance limit curve of the tested separation medium. Since the kinetic performance limit curve is based on an extrapolation to columns with a different length, it should be realized that the curve is only valid under the assumption that the gradient time and the delay time (if any) are adapted such that the analytes are subjected to the same relative mobile phase history when the column length is changed. Both experimental and numerical data are presented to corroborate the fact that the kinetic performance limit curves that are obtained using the proposed expressions are indeed independent of the column length the experimental data were collected in. Deviations might arise if excessive viscous heating occurs in columns with a pronounced non-adiabatic thermal behaviour.
    Journal of Chromatography A 02/2010; 1217(17):2787-95. DOI:10.1016/j.chroma.2010.02.023 · 4.26 Impact Factor
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    ABSTRACT: a b s t r a c t Micrometer sized spherical mesoporous MCM-41 particles were synthesized to use as a packing material for High Performance Liquid Chromatography. Spray drying was used for the synthesis of the particles and this enables easy up scaling. The entire synthetic procedure was optimized to ensure optimum particle morphology while preserving a high surface area and acceptable yields. The resulting material, with an average particle size of 1.8 lm, a narrow size distribution and a large porosity was subsequently grafted with C18 groups, packed into column assemblies and evaluated by reversed phase HPLC. The packing remained stable during the entire series of HPLC analysis, which were performed (>300 runs). Moreover the high accessible surface area leads to superior retention factors (doubling the best perform-ing commercial columns) opening prospects for, e.g., the analysis of difficult mixtures of highly polar components.
    Microporous and Mesoporous Materials 01/2010; 142(1):282. DOI:10.1016/j.micromeso.2010.12.013 · 3.21 Impact Factor
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    34th International symposium on High Performance Liquid Phase Separations and Related Techniques (HPLC 2009); 06/2009