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Chen X.-J.,Lawrence Berkeley National Laboratory | Dinh N.P.,Umeå University | Dinh N.P.,Merck SeQuant AB | Zhao J.,University of Macau | And 3 more authors.
Journal of Separation Science | Year: 2012

Both poly(styrene-co-vinylbenzyl chloride-co-divinylbenzene) and poly(4-methylstyrene-co-vinylbenzyl chloride-co-divinylbenzene) monolithic columns have been hypercrosslinked and for the first time used to achieve capillary electrochromatographic separations. Although these columns do not contain ionizable functionalities, electroosmotic flow was observed due to adsorption of ions from a buffer solution contained in the mobile phase on the surface of the hydrophobic polymer. An increase of more than one order of magnitude was observed with the use of bothmonolithic polymers. The hypercrosslinking reaction creates a large surface area thus enabling adsorption of a much larger number of ions. Alkylbenzenes were successfully separated using the hypercrosslinked monolithic columns. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA.


Lindner U.,BAM Federal Institute of Materials Research and Testing | Lingott J.,BAM Federal Institute of Materials Research and Testing | Richter S.,BAM Federal Institute of Materials Research and Testing | Jiang W.,Merck SeQuant AB | And 4 more authors.
Analytical and Bioanalytical Chemistry | Year: 2015

Abstract Hydrophilic interaction chromatography (HILIC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) were optimised for the direct determination of gadolinium-based contrast agents in tap water. In comparison to our previous work, a new developed zwitterionic HILIC column (ZIC-cHILIC) was used for speciation of Gd-containing contrast agents. The limit of quantification (LOQ) for the five contrast agents Gd-BOPTA, Gd-DPTA-BMA, Gd-BT-DO3A, Gd-DOTA and Gd-DTPA are in the range of 5-12 ng Gd per litre. Additionally, a new internal standard, Pr-DOTA, was investigated to correct intensity drifts, minor and major changes in the sample volumes and possible matrix effects. With the speciation method described, tap water samples from the area of Berlin were analysed and for the first time, three Gd species, Gd-BT-DO3A, Gd-DOTA and Gd-BOPTA, were found in tap water samples at concentrations of about 10-20 ng Gd per litre. These are the same Gd species which have been previously detected predominantly in surface waters of the Berlin area. © 2014 Springer-Verlag Berlin Heidelberg.


Bystrom E.,Umeå University | Viklund C.,Merck SeQuant AB | Irgum K.,Umeå University
Journal of Separation Science | Year: 2010

Nitroxide-mediated polymerization was used as a model system for preparing styrenic monolithic materials with significant mesopore contents in different mold formats, with the aim of assessing the validity of pore characterization of capillary monoliths by analysis of parallel bulk polymerized precursor solution. Capillary monoliths were prepared in 250 μm id fused silica tubes (quadruplicate samples, in total 17 m), and the batch polymerizations were carried out in parallel in 100 μL microvials and regular 2mL glass vials, both in quintuplicate. The monoliths recovered from the molds were characterized for their meso- and macroporous properties by nitrogen sorptiometry (three repeated runs on each sample), followed by a single analysis by mercury intrusion porosimetry. A total of 14 monolith samples were thus analyzed. A Grubbs' test identified one regular vial sample as an outlier in the sorptiometric surface area measurements, and data from this sample were consequently excluded from the pore size calculations, which are based on the same nitrogen sorption data, and also from the mercury intrusion data set. The remaining data were subjected to single factor analyses of variance analyses to test if the porous properties of the capillary monoliths were different from those of the bulk monoliths prepared in parallel. Significant differences were found between all three formats both in their meso-and macroporous properties. When the dimension was shrunk from conventional vial to capillary size, the specific surface area decreased from 52.2±4.7 to 34.6±1.7m 2/g. This decrease in specific surface area was accompanied by a significant shift in median diameter of the through-pores, from 310±3.9 to 544±13 nm. None of these differences were obvious from the scanning electron micrographs that were acquired for each sample type. The common practice of determining the mesopore characteristics from analysis of samples prepared by parallel bulk polymerization and looking for changes in the macropore structure by visual assessment of SEMs are therefore both rather questionable, at least for monoliths of the kind used in this study. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.


Ihunegbo F.N.,Telemark University College | Ihunegbo F.N.,Umeå University | Tesfalidet S.,Umeå University | Jiang W.,Merck SeQuant AB
Journal of Separation Science | Year: 2010

A hydrophilic interaction liquid chromatography-UV method was developed for the determination of melamine in milk powder. Sulfobetaine type zwitterionic hydrophilic interaction liquid chromatography stationary phase was used to achieve straightforward separation of melamine in milk powder without any sample derivatization or addition of ion-pair reagent. The sample preparation was simple and fast with the steps of acetonitrile/ perchloric acid extraction-centrifugation-filtration. No SPE or other pre-concentration procedure was required. By using large volume sample injection and choosing low UV wavelength (210 nm), the LOD and LOQ were 0.005 and 0.015 mg/mL for melamine standards, and 0.02 and 0.06 μg/mL for the spiked milk extracts. The LOD and LOQ of the latter correspond to 0.95 and 2.2 μg/g melamine in the milk powder. The correlation coefficients for melamine standard, pre-spiked milk extracts and post-spiked milk extracts in the range of 0-0.5 mg/mL were 0.9978, 0.9976 and 0.9995, respectively. This newly developed method is sensitive and cost effective, therefore, suitable for screening of melamine in tainted milk products. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Dinh N.P.,Umeå University | Dinh N.P.,Merck SeQuant AB | Jonsson T.,Merck SeQuant AB | Irgum K.,Umeå University
Journal of Chromatography A | Year: 2013

Since water associated with the stationary phase surface appears to be the essence of the retention mechanism in hydrophilic interaction chromatography (HILIC), we developed a method to characterize the water-absorbing capabilities of twelve different HILIC stationary phases. Adsorption isotherms for non-modified and monomerically functionalized silica phases adhered to a pattern of monolayer formation followed by multilayer adsorption, whereas water uptake on polymerically functionalized silica stationary phases showed the characteristics of formation and swelling of hydrogels. Water accumulation was affected by adding ammonium acetate as buffer electrolyte and by replacing 5% of the acetonitrile with tertiary solvents capable of hydrogen bonding such as methanol or tetrahydrofuran. The relationship between water uptake and retention mechanism was investigated by studying the correlations between retention factors of neutral analytes and the phase ratios of HILIC columns, calculated either from the surface area (adsorption) or the volume of the water layer enriched from the acetonitrile/water eluent (partitioning). These studies made it evident that adsorption and partitioning actually coexist as retention promoters for neutral solutes in the water concentration regime normally encountered in HILIC. Which factors that dominates is dependent on the nature of the solute, the stationary phase, and the eluting conditions. © 2013.


Bui N.T.H.,Umeå University | Jiang W.,Merck SeQuant AB | Sparrman T.,Umeå University | Irgum K.,Umeå University
Journal of Separation Science | Year: 2012

Porous silica coated by a highly hydrophilic and nonionic tentacle-type polymeric layer was synthesized by free radical "grafting from" polymerization of N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]-2-propenamide (TRIS-acrylamide) in partly aqueous solutions. The radical initiator sites were incorporated on the silica surfaces via a two-step reaction comprising thionyl chloride activation and subsequent reaction with tert-butyl hydroperoxide. The surface-bound tert-butylperoxy groups were then used as thermally triggered initiators for graft polymerization of TRIS-acrylamide. The synthesized materials were characterized by diffusive reflectance Fourier transform infrared specotroscopy, X-ray photoelectron spectroscopy, and CHN elemental analysis. Photon correlation spectroscopy was used to determine changes in ζ-potentials resulting from grafting, 29Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR) spectroscopy was used to assess the ratio of silanol to siloxane groups in the substrate and the grafted material, and the changes in surface area and mesopore distribution were determined by nitrogen cryosorption. Chromatographic evaluation in hydrophilic interaction chromatography (HILIC) mode showed that the materials were suitable for use as stationary phases, featuring good separation efficiency, a comparatively high retention, and a selectivity that differed from most commercially available HILIC phases. A comparison of this neutral phase with a previously reported N-(2-hydroxypropyl)-linked TRIS-type hydrophilic tentacle phase with weak anion exchange functionality revealed substantial differences in retention patterns. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wohlgemuth J.,Merck KGaA | Karas M.,Goethe University Frankfurt | Jiang W.,Merck SeQuant AB | Hendriks R.,Merck KGaA | Andrecht S.,Merck KGaA
Journal of Separation Science | Year: 2010

Dedicated and specific sample preparation and adequate chromatographic resolution prior to MS are necessary for comprehensive and site-specific glycosylation analysis to compensate for high heterogeneity of protein glycosylation, low-abundance of specific glycoforms and ion-suppression effects caused by coelution of other peptides. This article describes a scheme for glycopeptide profiling, which comprises HILIC batch enrichment followed by complementary HILIC and RP-LC in 1-D and 2-D approaches. For reproducible and sensitive nano-LC/ESI-MS analysis, we used ZIC-HILIC and RP18e monolithic silica capillaries and assessed their retention characteristics and complementarity for glycopeptide separations. The experiments revealed that pre-enrichment of glycopeptides in combination with LC employing both phases considerably improves sitespecific elucidation of glycosylation heterogeneity. Zwitterionic hydrophilic interaction liquid chromatography showed high capability to separate glycopeptides by their glycan composition, which coeluted on RP18e. By varying solvent conditions, retention can be well tuned, and efficient separations were achieved even in absence of any additives like salt or formic acid. RP18e facilitated glycopeptide separations with high peak capacity based on peptide sequence and degree of sialylation. Implementing both orthogonal and complementary phases in 1-D and 2-D LC setups was shown to significantly increase the number of different identified glycoforms and possesses great potential for comprehensive glycoproteomics approaches. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wikberg E.,Umeå University | Sparrman T.,Umeå University | Viklund C.,Merck SeQuant AB | Jonsson T.,Merck SeQuant AB | Irgum K.,Umeå University
Journal of Chromatography A | Year: 2011

2H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases for liquid chromatography at temperatures between -80 and +4°C. The fraction of water that remained unfrozen in four different neat silicas with nominal pore sizes between 60 and 300Å, and in silicas with polymeric sulfobetaine zwitterionic functionalities prepared in different ways, could be determined by measurements of the line widths and temperature-corrected integrals of the 2H signals. The phase transitions detected during thawing made it possible to estimate the amount of non-freezable water in each phase. A distinct difference was seen between the neat and modified silicas tested. For the neat silicas, the relationship between the freezing point depression and their pore size followed the expected Gibbs-Thomson relationship. The polymeric stationary phases were found to contain considerably higher amounts of non-freezable water compared to the neat silica, which is attributed to the structural effect that the sulfobetaine polymers have on the water layer close to the stationary phase surface. The sulfobetaine stationary phases were used alongside the 100Å silica to separate a number of polar compounds in hydrophilic interaction (HILIC) mode, and the retention characteristics could be explained in terms of the surface water structure, as well as by the porous properties of the stationary phases. This provides solid evidence supporting a partitioning mechanism, or at least of the existence of an immobilized layer of water into which partitioning could be occurring. © 2011 Elsevier B.V.


Dinh N.P.,Umeå University | Dinh N.P.,Merck SeQuant AB | Jonsson T.,Merck SeQuant AB | Irgum K.,Umeå University
Journal of Chromatography A | Year: 2011

This work aims at characterizing interactions between a select set of probes and 22 hydrophilic and polar commercial stationary phases, to develop an understanding of the relationship between the chemical properties of those phases and their interplay with the eluent and solutes in hydrophilic interaction chromatography. " Hydrophilic interaction" is a somewhat inexact term, and an attempt was therefore made to characterize the interactions involved in HILIC as hydrophilic, hydrophobic, electrostatic, hydrogen bonding, dipole-dipole, π-π interaction, and shape-selectivity. Each specific interaction was quantified from the separation factors of a pair of similar substances of which one had properties promoting the interaction mode being probed while the other did not. The effects of particle size and pore size of the phases on retention and selectivity were also studied. The phases investigated covered a wide range of surface functional groups including zwitterionic (sulfobetaine and phosphocholine), neutral (amide and hydroxyl), cationic (amine), and anionic (sulfonic acid and silanol). Principal component analysis of the data showed that partitioning was a dominating mechanism for uncharged solutes in HILIC. However, correlations between functional groups and interactions were also observed, which confirms that the HILIC retention mechanism is partly contributed by adsorption mechanisms involving electrostatic interaction and multipoint hydrogen bonding. Phases with smaller pore diameters yielded longer retention of solutes, but did not significantly change the column selectivities. The particle diameter had no significant effect, neither on retention, nor on the selectivities. An increased water content in the eluent reduced the multipoint hydrogen bonding interactions, while an increased electrolyte concentration lowered the selectivities of the tested columns and made their interaction patterns more similar. © 2011.


Marrubini G.,University of Pavia | Pedrali A.,University of Pavia | Hemstrom P.,Merck SeQuant AB | Jonsson T.,Merck SeQuant AB | And 2 more authors.
Journal of Separation Science | Year: 2013

Short-chain carboxylic acids are relevant in pharmaceutical, food quality control, and biomedical analysis. In this study, 11 acids commonly found in drugs and in food products were selected. Wine was chosen as matrix for testing the method. The test compounds were used for comparing the selectivity of four 150 × 2.1 mm zwitterionic hydrophilic interaction LC (HILIC) columns (ZIC-HILIC 5 μm, 200 Å, and 3.5 μm, 100 Å, ZIC-pHILIC 5 μm, ZIC-cHILIC 3 μm, 100 Å) while varying the conditions to optimize for low UV wavelength detection and achieve high sensitivity. Retention using potassium phosphate and ammonium carbonate as mobile-phase components at pH 6.0, 7.5, and 8.5-8.9 was studied considering recent hypotheses on HILIC mechanism-related with the Hofmeister series effect and ion hydration. An isocratic method with UV detection at 200 nm and mobile phase consisting of 75% acetonitrile and 10 mM potassium phosphate at pH 6.0 applied to a ZIC-cHILIC column was found provisionally optimal and partially validated for the 11 analytes. Satisfactory results (R2 from 0.9940 to >0.9999), and recoveries from 93-106% for all analytes evidenced the method as suitable for wine analysis. To the best of our knowledge, no previous study has reported on the direct ZIC-HILIC separation and UV detection of the acids considered here in wine. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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