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Ihunegbo F.N.,Telemark University College | Ihunegbo F.N.,Umea University | Tesfalidet S.,Umea 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.

Bui N.T.H.,Umea University | Jiang W.,Merck SeQuant AB | Sparrman T.,Umea University | Irgum K.,Umea 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.

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.

Chen X.-J.,Lawrence Berkeley National Laboratory | Dinh N.P.,Umea 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.

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