ORCID Profile
0000-0002-9167-7716
Current Organisation
University of Amsterdam
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Publisher: Elsevier BV
Date: 11-2012
DOI: 10.1016/J.CHROMA.2012.09.080
Abstract: Detailed characterization of synthetic polymers often required multiple advanced separation technologies since the various molecular distributions present, e.g. polymer molar mass, chemical composition, functionality distributions, etc. are generally mutually dependent. The complexity of polymeric materials necessitates the use of a variety of analytical methods, either in conjunction or in integrated ("hyphenated") systems. Poly(2-oxazoline) homo- and copolymers with two different side groups rendering the systems hydrophobic, i.e. phenyl and dec-9-enyl substituents, synthesized by living cationic ring-opening polymerization, were investigated. The average chemical composition obtained by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) corresponded well with the theoretical composition. The chemical-composition distribution was studied with gradient elution liquid chromatography (GELC) using water and tetrahydrofuran as mobile-phase components. Statistical copolymer s les - in contrast to their block copolymer analogues - revealed two well-separated peaks in GELC. By combining GELC with size-exclusion chromatography (SEC) it was confirmed that the GELC separation was not based on differences in the molar mass. A more likely explanation of the GELC results is the presence of an ionic fraction in the s les of statistical copolymers resulting from either chain-transfer reactions or termination by addition of water. This hypothesis was confirmed with capillary electrophoresis.
Publisher: Elsevier BV
Date: 03-2005
DOI: 10.1016/J.CHROMA.2004.11.081
Abstract: A capacitively coupled contactless conductivity detection (CCD) system has been applied for the detection of neutral synthetic polymers in capillary size-exclusion electrokinetic chromatography (SEEC). Polystyrene standards, that were used as a model compounds, were separated on a capillary column packed with porous 10 microm silica particles with an electrokinetically driven mobile phase, and detected by CCD and UV detection simultaneously. Mass-calibration curves for polystyrene were constructed. Satisfactory results were obtained for the linearity, the run-to-run repeatability (<0.2% for the relative retention and <4% for the peak area) and the robustness of the detector. One of the major issues in this preliminary study was to investigate the origin of the peaks observed for the polystyrene standards. The effect of the molar mass of the polystyrenes on the sensitivity was small. Therefore, the signals obtained could not be explained as the result of an increased viscosity and a decreased solution conductivity of the solute zone. An alternative hypothesis is suggested, and recommendations for further research are given.
Publisher: Elsevier BV
Date: 04-2007
DOI: 10.1016/J.CHROMA.2007.01.109
Abstract: A new resolution metric for two-dimensional chromatography is proposed and tested. This resolution measurement is based on the concept of the (one-dimensional) valley-to-peak ratio, which has been adapted and modified for two-dimensional chromatography. Two questions are considered related to the computation of the resolution of a given (two-dimensional) peak. First, the concept of peak neighbourhood is revised, since it changes drastically from one- to two-dimensional chromatography. In a chromatogram resulting from a two-dimensional analysis, one peak may be surrounded by more than two neighbouring peaks. However, the neighbouring peaks can be remote from the peak or some interfering peaks may be in between. In these cases, it is not meaningful to compute the resolution between them. A method is proposed to determine whether a resolution measurement between two two-dimensional peaks is reasonable. Second, a measurement of the valley-to-peak ratio in two-dimensional chromatography is proposed. The measurement is based on the concept of the saddle point (which is defined for two-dimensional surface plots). A study of the correlation of the valley-to-peak ratio with the error obtained for quantification is presented. The new metric can be used as an estimator of the quantification errors. Also, valley-to-peak ratios can be calculated for one or more target peak(s) to estimate the separation quality of the entire chromatogram. This makes the proposed measurement suitable for optimisation purposes. Although the algorithm was developed for GC x GC, preliminary studies suggested that its application to other two-dimensional separation methods (e.g. LC x LC) should only require minor modification (if any).
Publisher: Elsevier BV
Date: 07-2007
DOI: 10.1016/J.CHROMA.2006.10.066
Abstract: A method for peak detection in two-dimensional chromatography is presented. The algorithm applies first the methods developed for peak detection in one-dimensional chromatography to detect peaks in one dimension. In a second step, a decision tree is applied to decide which one-dimensional peaks are originated from the same compound and have to be 'merged' into one two-dimensional peak. To this end, different features of the peaks (second-dimension peak regions and second-dimension retention times) are compared and different criteria (common peak regions, retention time differences, unimodality in the first dimension) are applied. Different options can be used, depending on the nature of the data. The user controls this decision tree by establishing several options and "switches". The algorithm was tested with GCxGC chromatograms obtained for a commercial air-freshener s le, detecting and merging the modulated peaks belonging to the same compound. Recommendations for the set of options and switches are given. A utility that calculates and sums peak areas from merged peaks is added to facilitate automated quantification. Although the algorithm was developed for GCxGC, its application to comprehensive two-dimensional liquid chromatography (LCxLC) data should at most require minor modifications.
Publisher: Wiley
Date: 02-2007
Abstract: Preparation of monolithic capillary columns for separations in the CEC mode using UV-initiated polymerization of the plain monolith followed by functionalization of its pore surface by photografting has been studied. The first step enabled the preparation of generic poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths with optimized porous properties, controlled by the percentages of porogens 1-decanol and cyclohexanol in the polymerization mixture, irradiation time, and UV light intensity. Ionizable monomers [2-(methacryloyloxy)ethyl]trimethylammonium chloride or 2-acryloamido-2-methyl-1-propanesulfonic acid were then photografted onto the monolithic matrix, allowing us to control the direction of the EOF in CEC. Different strategies were applied to control the grafting density and, thereby, the magnitude of the EOF. To control the hydrophobic properties, two approaches were tested: (i) cografting of a mixture of the ionizable and hydrophobic monomers and (ii) sequential grafting of the ionizable and hydrophobic monomers. Cografting resulted in similar retention but higher EOF. With sequential grafting, more than 50% increase in retention factors was obtained and a slight decrease in EOF was observed due to shielding of the ionizable moieties.
Publisher: Elsevier BV
Date: 08-2022
DOI: 10.1016/J.CHROMA.2022.463386
Abstract: Synthetic polymers typically show dispersity in molecular weight and potentially in chemical composition. For the analysis of the chemical-composition distribution (CCD) gradient liquid chromatography may be used. The CCD obtained using this method is often convoluted with an underlying molecular-weight distribution (MWD). In this paper we demonstrate that the influence of the MWD can be reduced using very steep gradients and that such gradients are best realized utilizing recycling gradient liquid chromatography (LC↻LC). This method allows for a more-accurate determination of the CCD and the assessment of (approximate) critical conditions (if these exist), even when high-molecular-weight standards of narrow dispersity are not readily available. The performance and usefulness of the approach is demonstrated for several polystyrene standards, and for the separation of statistical copolymers consisting of styrene/methyl methacrylate and methyl methacrylate/butyl methacrylate. For the latter case, approximate critical compositions of the copolymers were calculated from the critical compositions of two homopolymers and one copolymer of known chemical composition, allowing for a determination of the CCD of unknown s les. Using this approach it is shown that the copolymers elute significantly closer to the predicted critical compositions after recycling of the gradient. This is most clear for the lowest-molecular-weight copolymer (M
No related grants have been discovered for Peter Schoenmakers.