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  • 1. Al-Jarah, S. Y.
    et al.
    Sjodahl, J.
    Woldegiorgis, A.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Capillary electrophoretic and mass spectrometric analysis of a polydisperse fluorosurfactant2005In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 28, no 3, p. 239-244Article in journal (Refereed)
    Abstract [en]

    A fluorosurfactant has been studied using capillary electrophoresis and mass spectrometry. The fluorosurfactant, FC134, can be used as a buffer additive in capillary electrophoresis in order to decrease wall adsorption of proteins and in micellar electrokinetic chromatography. However, it has been discovered that this fluorosurfactant is polydisperse, thus containing substances with different lengths and structures. In this work, the fluorosurfactant sample components were separated by capillary electrophoresis. An uncoated as well as a poly(vinyl alcohol)-coated capillary were used with running electrolytes containing methanol and acetic acid. Following the capillary electrophoretic separation, fractions were collected for further analysis by MALDI-MS. Non-fractionated samples were also analyzed both by MALDI-MS and by ESI-MS.

  • 2. Dominguez, Marina A.
    et al.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Centurion, Maria E.
    Capillary electrophoresis method for the simultaneous determination of carbohydrates and proline in honey samples2016In: Microchemical journal (Print), ISSN 0026-265X, E-ISSN 1095-9149, Vol. 129, p. 1-4Article in journal (Refereed)
    Abstract [en]

    A capillary electrophoresis method with indirect UV detection for the simultaneous determination of three carbohydrates (fructose, glucose and sucrose) and the amino acid proline in honey samples was developed. This method included the use of a background electrolyte consisting of 10 mM sodium benzoate and 1.5 mM cetyltrimethylammonium bromide, pH 12.4. Under optimal capillary electrophoresis conditions, the separation of the investigated substances was achieved in less than 5 min and single dilution of each sample was employed. The detection limits for fructose, glucose and sucrose were 0.58 g L-1, 0.67 g L-1 and 0.12 g L-1 respectively, and 0.72 mg L-1 for proline. Precision measurements calculated in terms of %RSD in the range of 0.92 to 5.43%, were obtained. The proposed method was applied to honey samples from Argentina and Sweden and enables the determination of the three carbohydrates and the amino acid proline. The results show that the proposed method is simple, requires short analysis times, low consumption of reagents and sample, minimum waste and that there is no need to perform any sample pre-treatment. This method is a good alternative to carry out the quality control of honey samples. Finally, it is a promising methodology for achieving green chemistry goals.

  • 3.
    Ek, Patrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Schönberg, Tommy
    Sjödahl, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Vieider, Christian
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Roeraade, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Electrospray Ionization from an Adjustable Gap between two Silicon Chips2009In: Journal of Mass Spectrometry, ISSN 1076-5174, E-ISSN 1096-9888, Vol. 44, no 2, p. 171-181Article in journal (Refereed)
    Abstract [en]

    In this paper, a silicon chip - based electrospray emitter with a variable orifice size is presented. The device consists of two chips, with a thin beam elevating from the center of each of the chips. The chips are individually mounted to form an open gap of a narrow, uniform width between the top areas of the beams. The electrospray is generated at the endpoint of the gap, where the spray point is formed by the very sharp intersection between the crystal planes of the < 100 > silicon chips. Sample solution is applied to the rear end of the gap from a capillary via a liquid bridge, and capillary forces ensure a spontaneous imbibition of the gap. The sample solution is confined to the gap by means of a hydrophobic treatment of the surfaces surrounding the gap, as well as the geometrical boundaries formed by the edges of the gap walls. The gap width could be adjusted between 1 and 25 μm during electrospray experiments without suffering from any interruption of the electrospray process. Using a peptide sample solution, a shift toward higher charge states and increased signal-to-noise ratios was observed when the gap width was decreased. The limit of detection for the peptide insulin (chain B, oxidized) was approximately 4 nM. We also show a successful interfacing of the electrospray setup with capillary electrophoresis.

  • 4.
    Ek, Patrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Stjernström, Mårten
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Roeraade, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Electrospray ionization mass spectrometry from discrete nanoliter-sized sample volumes2010In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 24, no 17, p. 2561-2568Article in journal (Refereed)
    Abstract [en]

    We describe a method for nanoelectrospray ionization mass spectrometry (nESI-MS) of very small sample volumes. Nanoliter-sized sample droplets were taken up by suction into a nanoelectrospray needle from a silicon microchip prior to ESI. To avoid a rapid evaporation of the small sample volumes, all manipulation steps were performed under a cover of fluorocarbon liquid. Sample volumes down to 1.5 nL were successfully analyzed, and an absolute limit of detection of 105 attomole of insulin (chain B, oxidized) was obtained. The open access to the sample droplets on the silicon chip provides the possibility to add reagents to the sample droplets and perform chemical reactions under an extended period of time. This was demonstrated in an example where we performed a tryptic digestion of cytochrome C in a nanoliter-sized sample volume for 2.5h, followed by monitoring the outcome of the reaction with nESI-MS. The technology was also utilized for tandem mass spectrometry (MS/MS) sequencing analysis of a 2 nL solution of angiotensin I.

  • 5. Emmer, Åsa
    et al.
    JANSSON, M
    ROERAADE, J
    A NEW APPROACH TO DYNAMIC DEACTIVATION IN CAPILLARY ZONE ELECTROPHORESIS1991In: HRC Journal of High Resolution Chromatography, ISSN 0935-6304, E-ISSN 1521-4168, Vol. 14, no 11, p. 738-740Article in journal (Refereed)
  • 6. EMMER, Åsa
    et al.
    JANSSON, M
    ROERAADE, J
    IMPROVED CAPILLARY ZONE ELECTROPHORETIC SEPARATION OF BASIC-PROTEINS, USING A FLUOROSURFACTANT BUFFER ADDITIVE1991In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 547, no 1-2, p. 544-550Article in journal (Refereed)
  • 7. Emmer, Åsa
    et al.
    JANSSON, M
    ROERAADE, J
    SEPARATION OF PIG-LIVER ESTERASE ISOENZYMES AND SUBUNITS BY CAPILLARY ZONE ELECTROPHORESIS IN THE PRESENCE OF FLUORINATED SURFACTANTS1994In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 672, no 1-2, p. 231-236Article in journal (Refereed)
  • 8. Emmer, Åsa
    et al.
    JANSSON, M
    ROERAADE, J
    LINDBERG, U
    HOK, B
    FABRICATION AND CHARACTERIZATION OF A SILICON MICROVALVE1992In: Journal of Microcolumn Separations, ISSN 1040-7685, E-ISSN 1520-667X, Vol. 4, no 1, p. 13-15Article in journal (Refereed)
  • 9. Emmer, Åsa
    et al.
    ROERAADE, J
    CAPILLARY ELECTROPHORESIS, COMBINED WITH AN ONLINE MICRO POSTCOLUMN ENZYME ASSAY1994In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 662, no 2, p. 375-381Article in journal (Refereed)
  • 10. Emmer, Åsa
    et al.
    ROERAADE, J
    MICRO ENZYMATIC ASSAY COUPLED TO CAPILLARY ELECTROPHORESIS VIA LIQUID-JUNCTION1994In: Chromatographia, ISSN 0009-5893, E-ISSN 1612-1112, Vol. 39, no 5-6, p. 271-278Article in journal (Refereed)
  • 11. Emmer, Åsa
    et al.
    ROERAADE, J
    PERFORMANCE OF ZWITTERIONIC AND CATIONIC FLUOROSURFACTANTS AS BUFFER ADDITIVES FOR CAPILLARY ELECTROPHORESIS OF PROTEINS1994In: JOURNAL OF LIQUID CHROMATOGRAPHY, ISSN 0148-3919, Vol. 17, no 18, p. 3831-3846Article in journal (Refereed)
  • 12.
    Emmer, Åsa
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Roeraade, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Enzymatic protein digest in chip-based nanovials with immobilized proteolytic enzymes2005In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 542, no 2, p. 137-143Article in journal (Refereed)
    Abstract [en]

    In the present work, protein digest reactions in silicon-based microchips, coated with immobilized proteolytic enzymes, have been carried out. The performance of such vials, modified with trypsin or chymotrypsin, was tested with myoglobin as a substrate. Capillary electrophoresis and matrix-assisted laser desorption/ionization mass spectrometry were utilized for analysis of the digests, and the influence of different instrumentation setups. immobilization procedures and reaction conditions are discussed.

  • 13.
    Emmer, Åsa
    et al.
    KTH, Superseded Departments, Chemistry.
    Roeraade, Johan
    KTH, Superseded Departments, Chemistry.
    Wall deactivation with fluorosurfactants for capillary electrophoretic analysis of biomolecules2001In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 22, no 4, p. 660-665Article in journal (Refereed)
    Abstract [en]

    This paper describes the use of fluorosurfactants as buffer additives for capillary electrophoretic separation of proteins and peptides. Due to fluorosurfactant bilayer formation at the capillary inner wall, the surface charge can be adjusted and even reversed. If the running buffer pH is kept at a level where the proteins have the same sign of charge as the wall, electrostatic repulsion will be obtained. The protein wall adsorption can therefore be reduced and the separation performance can be noticeably increased. The separation performance can also be further improved by including mixtures of different types of fluorosurfactants in the running buffer. The buffer system can accordingly be adapted for a certain separation problem. Mechanisms for the use of fluorosurfactants for wall deactivation in capillary electrophoretic protein separations is discussed in the present work and some examples of applications are also presented.

  • 14. Gao, Qiuju
    et al.
    Araia, Musie
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Leck, Caroline
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Characterization of exopolysaccharides in marine colloids by capillary electrophoresis with indirect UV detection2010In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 662, no 2, p. 193-199Article in journal (Refereed)
    Abstract [en]

    A method was established using capillary electrophoresis with indirect UV detection for analysis of monosaccharides liberated from exopolysaccharides by acidic hydrolysis. Tangential flow filtration was used to isolate high molecular weight polysaccharides from seawater. The capillary electrophoresis method included the use of a background electrolyte consisting of 2,6-dimethoxyphenol and cetyltrimethylammonium bromide. Several neutral sugars commonly existing in marine polysaccharides were separated under optimized conditions. The relative standard deviations were between 1.3% and 2.3% for relative migration time and 1.3-2.5% for peak height. Detection limits (at S/N 3) were in the range of 27.2-47.8 mu M. The proposed approach was applied to the analysis of hydrolyzed colloidal polysaccharides in seawater collected from the Baltic Sea. Nanomolar levels of liberated monosaccharides in seawater samples can be detected by preconcentration up to 30,000 times.

  • 15.
    Hedberg, Yolanda
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Lundin, Maria
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Blomberg, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Wallinder, Inger Odnevall
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Chromium-protein complexation studies by adsorptive cathodic stripping voltammetry and MALDI-TOF-MS2012In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 42, no 5, p. 349-358Article in journal (Refereed)
    Abstract [en]

    A methodology using stripping voltammetry has been elaborated to enable sensitive and reliable protein-chromium complexation measurements. Disturbing effects caused by adsorption of proteins on the mercury electrode were addressed. At low concentrations of proteins (< 60-85 nM), chromium-protein complexation measurements were possible. Chromium(VI) complexation was quantitatively determined using differently sized, charged, and structured proteins: serum albumin (human and bovine), lysozyme, and mucin. Generated results showed a strong relation between complexation and protein size, concentration, and the number of amino acids per protein mass. Complexation increased nonlinearly with increasing protein concentrations. The nature of this complexation was based on weak interactions judged from combined results with MALDI-TOF-MS and adsorptive cathodic stripping voltammetry.

  • 16. Hellborg, Karin
    et al.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Skedung, Lisa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Redeby, Therese
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Evaluation of MALDI matrices and digestion methods aiming at MS analysis of hydrophobic proteins and peptidesManuscript (Other academic)
  • 17.
    Hult, E L
    et al.
    KTH, Superseded Departments, Chemistry.
    Emmer, Åsa
    KTH, Superseded Departments, Chemistry.
    Roeraade, Johan
    KTH, Superseded Departments, Chemistry.
    Capillary electrophoretic separation of acidic and basic proteins in the presence of cationic and anionic fluorosurfactants1997In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 757, no 1-2, p. 255-262Article in journal (Refereed)
  • 18.
    Jacksén, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Dahl, Kenneth
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Karlberg, Ann-Therese
    Redeby, Theres
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Capillary electrophoresis separation and matrix-assisted laser desorption/ionization mass spectrometry characterization of bovine serum albumin fluorescein isothiocyanate conjugates2010In: Journal of chromatography. B, ISSN 1570-0232, E-ISSN 1873-376X, Vol. 878, no 15-16, p. 1125-1134Article in journal (Refereed)
    Abstract [en]

    A protocol using enzymatic digestion, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and capillary electrophoresis with laser induced fluorescence detection (CE-LIF) for the investigation of the binding of the fluorescent contact allergen fluorescein isothiocyanate (FITC) to the 66 kDa large protein bovine serum albumin (BSA), as a model system for protein-hapten binding in the skin, is presented. Mass spectra of BSA-FITC digestions, using trypsin and chymotrypsin, respectively, provided sequence coverage of 97%. To investigate the number of FITC-bound peptides using CE-LIF separation, three different buffer salts at four different pH levels were evaluated. The use of 20 mM sodium citrate pH 6.5 as well as 20 mM sodium phosphate pH 6.5 or pH 7.5 as background electrolyte revealed high numbers of peptides with at least one bound FITC. The effect of the electrolyte counter ion on MALDI-MS was investigated and was found to have effect on the MALDI spectra signal-to-noise (S/N) at 50 mM but not at 10 m M. Of the 60 theoretical FITC-binding sites in BSA this MALDI-MS protocol presents 30 defined. 28 possible and 2 non-binding sites for FITC. (C) 2010 Elsevier B.V. All rights reserved.

  • 19.
    Jacksén, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    CE analysis of single wood cells performing hydrolysis and preconcentration inopen micro channelsManuscript (preprint) (Other academic)
  • 20.
    Jacksén, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Evaluation of 2,6-dihydroxyacetophenone as MALDI matrix for analysis ofhydrophobic proteins and peptidesManuscript (preprint) (Other academic)
  • 21.
    Jacksén, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Evaluation of 2,6-dihydroxyacetophenone as matrix-assisted laser desorption/ionization matrix for analysis of hydrophobic proteins and peptides2012In: Analytical Biochemistry, ISSN 0003-2697, E-ISSN 1096-0309, Vol. 425, no 1, p. 18-20Article in journal (Refereed)
    Abstract [en]

    Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is widely used for analysis of macromolecules like peptides and proteins. The analysis procedure is generally simple but must be adapted to the characteristics of the analytes. Therefore, specific matrices suitable for, e.g., hydrophobic proteins and peptides that are difficult to analyze would be preferable in order to optimize the outcome. In the present work, 2,6-dihydroxyacetophenone (DHAP) was shown to be beneficial in comparison to DHB for intact bacteriorhodopsin (BR) as well as for chemically digested BR.

  • 22.
    Jacksén, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Frisk, Thomas
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Redeby, Theres
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Parmar, Varun
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    van der Wijngaart, Wouter
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Off-line integration of CE and MALDI-MS using a closed-open-closed microchannel system2007In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 28, no 14, p. 2458-2465Article in journal (Refereed)
    Abstract [en]

    In this work, a new technique for off-line hyphenation between CE and MALDI-MS is presented. Two closed fused-silica capillaries were connected via a silicon chip comprising an open microcanal. The EOF in the system was evaluated using mesityloxide or leucine-enkephalin as a sample and with a running buffer that rendered the analyte neutrally charged. Comparison was made between the EOF in a closed system (first capillary solely included in the electrical circuit) and in a closed-open system (first capillary and microcanal included in the electrical circuit). It was concluded that the experimental values of the EOF agreed with the theory. The influence of the capillary outer diameter on the peak dispersion was investigated using a closed-open-closed system (first capillary, microcanal and second capillary included in the electrical circuit). It was clearly seen that a capillary with 375 mu m od induced considerably higher peak dispersion than a 150 mu m od capillary, due to a larger liquid dead volume in the connection between the first capillary outlet and the microcanal. Mass spectrometric analysis has also been performed following CE separation runs in a closed-open-closed system with cytochrome c and lysozyme as model proteins. It was demonstrated that a signal distribution profile of the separated analytes could be recorded over a 30 mm long microcanal.

  • 23.
    Jacksén, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Redeby, Theres
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Capillary electrophoretic separation and fractionation of hydrophobic peptides onto a pre-structured matrix assisted laser desorption/ionization target for mass spectrometric analysis2006In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 29, no 2, p. 288-295Article in journal (Refereed)
    Abstract [en]

     A CE separation of hydrophobic peptides followed by fractionation onto a prestructured MALDI target and off-line MS analysis was performed. An improved and partially automated manufacturing procedure of the previously described MALDI target is presented. This target is structurally coated with silicone and especially developed for hydrophobic peptides and proteins. Here, the target plate was designed specifically for the CE fraction collection. Different solvents were evaluated to meet the requirements of peptide solubility and compatibility to both the CE and MALDI methods and to the fractionation procedure. CE-MALDI-MS analysis of nine highly hydrophobic peptides from cyanogen bromide-digested bacteriorhodopsin is demonstrated.

  • 24. JANSSON, M
    et al.
    EMMER, Åsa
    ROERAADE, J
    SOME DESIGN CONSIDERATIONS IN MINIATURIZED ELECTROKINETIC SEPARATION SYSTEMS1989In: HRC Journal of High Resolution Chromatography, ISSN 0935-6304, E-ISSN 1521-4168, Vol. 12, no 12, p. 797-807Article in journal (Refereed)
  • 25. JANSSON, M
    et al.
    EMMER, ÅSA
    ROERAADE, J
    LINDBERG, U
    HOK, B
    MICROVIALS ON A SILICON-WAFER FOR SAMPLE INTRODUCTION IN CAPILLARY ELECTROPHORESIS1992In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 626, no 2, p. 310-314Article in journal (Refereed)
  • 26. Jarmeus, Alf
    et al.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    CE determination of monosaccharides in pulp using indirect detection and curve-fitting2008In: Chromatographia, ISSN 0009-5893, E-ISSN 1612-1112, Vol. 67, no 1-2, p. 151-155Article in journal (Refereed)
    Abstract [en]

    In the present work a capillary electrophoretic method for the analysis of monosaccharides utilizing indirect UV-detection has been developed. Different probes for indirect detection have been assessed using model carbohydrate samples. Background electrolytes with or without addition of cetyltrimethylammonium bromide have also been evaluated regarding the separation power. Furthermore, a curve-fitting algorithm has been introduced to increase the separation resolution. The optimized method has been used for analysis of monosaccharides from an acidically hydrolyzed pulp sample.

  • 27.
    Josefsson, Leila
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Bernsteen, Jessica
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, Superseded Departments (pre-2005), Chemistry.
    Evaluation of ethylammonium nitrate as background electrolyte in capillary electrophoresisManuscript (preprint) (Other academic)
  • 28.
    Josefsson, Leila
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Larsson, Malin K.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institute, Sweden.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Analysis of polyvinyl alcohol microbubbles in human blood plasma using capillary electrophoresis2016In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 39, no 8, p. 1551-1558Article in journal (Refereed)
    Abstract [en]

    Recently, a new type of ultrasound contrast agent that consists of air-filled microbubbles stabilized with a shell of polyvinyl alcohol was developed. When superparamagnetic nanoparticles of iron oxide are incorporated in the polymer shell, a multimodal contrast agent can be obtained. The biodistribution and elimination pathways of the polyvinyl alcohol microbubbles are essential to investigate, which is limited with today's techniques. The aim of the present study was, therefore, to develop a method for qualitative and quantitative analysis of microbubbles in biological samples using capillary electrophoresis with ultraviolet detection. The analysis parameters were optimized to a wavelength at 260 nm and pH of the background electrolyte ranging between 11.9 and 12. Studies with high-intensity ultrasonication degraded microbubbles in water showed that degraded products and intact microbubbles could be distinguished, thus it was possible to quantify the intact microbubbles solely. Analysis of human blood plasma spiked with either plain microbubbles or microbubbles with nanoparticles demonstrated that it is possible to separate them from biological components like proteins in these kinds of samples.

  • 29. Litborn, E
    et al.
    Emmer, Åsa
    Roeraade, J
    Chip-based nanovials for tryptic digest and capillary electrophoresis1999In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 401, no 1-2, p. 11-19Article in journal (Refereed)
  • 30. Litborn, E.
    et al.
    Emmer, Åsa
    KTH, Superseded Departments, Chemistry.
    Roeraade, Johan
    KTH, Superseded Departments, Chemistry.
    Parallel reactions in open chip-based nanovials with continuous compensation for solvent evaporation2000In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 21, no 1, p. 91-99Article in journal (Refereed)
    Abstract [en]

    In an earlier report (Litborn, E., Emmer,,Angstrom., Roeraade, J., Anal. Chim. Acta 1999, 401, 11-19, we described a technique for performing chemistry in chip-based vials. A major problem, solvent evaporation, was partially remedied by using a closed humidity chamber. in this paper we report an improved technique for performing parallel reactions in open, 15 nL volume, chip-based vials. The evaporation of solvent from the reaction fluid was continuously compensated by addition of solvent via an array of microcapillaries. The suitability of the method was demonstrated by performing eight separate peptide maps of myoglobin in parallel, using the three enzymes trypsin, alpha-chymotrypsin and endoproteinase Glu-C. The total amount of myoglobin utilized to perform the eight digests was less than 100 pmol. The corresponding amount of enzymes was ca. 0.1 pmol per reaction. In order to evaluate the operating limits of the technique, a study of the evaporation of solvents from a series of vials with proportionally smaller volumes operated at different temperatures was performed. The results showed that the concept for continuous compensation of solvent evaporation should be applicable to reaction volumes down to 30 pL.

  • 31.
    Mikkonen, Saara
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ekström, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Selective enrichment of amyloid beta peptides using isotachophoresisManuscript (preprint) (Other academic)
  • 32.
    Mikkonen, Saara
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Mass spectrometric analysis of nanoscale sample volumes extracted from open microchannels after sample preconcentration applied on amyloid beta peptides2014In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 406, no 14, p. 3521-3524Article in journal (Refereed)
    Abstract [en]

    A new instrumental concept for extraction of nanovolumes from open microchannels (dimensions 150 mu m x 50 mu m, length 10 mm) manufactured on silicon microchips has been used in combination with a previously developed method for preconcentrating proteins and peptides in the open channels through electromigration. The extracted nanovolumes were further analyzed using nanoelectrospray ionization (nESI) or matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) directly or with subsequent enzymatic protein digestion in a nanodroplet prior to the MS analysis. Preconcentration of the samples resulted in a 15-fold sensitivity increase in nESI for a neurotensin solution, and using MALDI-MS, amyloid beta (A beta) peptides could be detected in concentrations down to 1 nM. The method was also successfully applied for detection of cell culture A beta.

  • 33.
    Mikkonen, Saara
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Roeraade, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Thormann, Wolfgang
    University of Bern, Clinical Pharmacology Laboratory, Institute for Infectious Diseases.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Microfluidic Isoelectric Focusing of Amyloid Beta Peptides Followed by Micropillar-Matrix-Assisted Laser Desorption Ionization-Mass Spectrometry2016In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882Article in journal (Refereed)
    Abstract [en]

    A novel method for preconcentration and purification of the Alzheimer’s disease related amyloid beta (Aβ) peptides by isoelectric focusing (IEF) in 75 nL microchannels combined with their analysis by micropillar-matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) is presented. A semiopen chip-based setup, consisting of open microchannels covered by a lid of a liquid fluorocarbon, was used. IEF was performed in a mixture of four small and chemically well-defined amphoteric carriers, glutamic acid, aspartyl-histidine (Asp-His), cycloserine (cSer), and arginine, which provided a stepwise pH gradient tailored for focusing of the C-terminal Aβ peptides with a pI of 5.3 in the boundary between cSer and Asp-His. Information about the focusing dynamics and location of the foci of Aβ peptides and other compounds was obtained using computer simulation and by performing MALDI-MS analysis directly from the open microchannel. With the established configuration, detection was performed by direct sampling of a nanoliter volume containing the focused Aβ peptides from the microchannel, followed by deposition of this volume onto a chip with micropillar MALDI targets. In addition to purification, IEF preconcentration provides at least a 10-fold increase of the MALDI-MS-signal. After immunoprecipitation and concentration of the eluate in the microchannel, IEF-micropillar-MALDI-MS is demonstrated to be a suitable platform for detection of Aβ peptides in human cerebrospinal fluid as well as in blood plasma.

  • 34.
    Mikkonen, Saara
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Rokhas, Maria Khihon
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Sample preconcentration in open microchannels combined with MALDI-MS2012In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 33, no 22, p. 3343-3350Article in journal (Refereed)
    Abstract [en]

    In this work, a method for preconcentrating samples in 1 cm long, 50-150 μm wide open microchannels is presented. Platinum electrodes were positioned at the channel ends, voltage was applied, and charged analyte was preconcentrated at the oppositely charged side during continuous supply of sample. The preconcentration was initially studied in a closed system, where an influence on the analyte position from a pH gradient, generated by water electrolysis, was observed. In the open channel, the analyte distribution after preconcentration was evaluated using MALDI-MS with the channel as MALDI target. MALDI matrix was applied with an airbrush or by electrospray matrix deposition and by using the latter technique higher degrees of crystallization in the channels were obtained. After preconcentrating a 1 nM cytochrome c solution for 5 min, corresponding to a supplied amount of 1.25 fmol, a signal on the cathodic channel end could be detected. When a solution of cytochrome c trypsin digest was supplied, the peptides were preconcentrated at different positions along the channel depending on their charge.

  • 35.
    Mikkonen, Saara
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Thormann, Wolfgang
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Computer simulations of sample preconcentration in carrier-free systems and isoelectric focusing in microchannels using simple ampholytes2015In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 36, no 19, p. 2386-2395Article in journal (Refereed)
    Abstract [en]

    In this work, electrophoretic preconcentration of protein and peptide samples in microchannels was studied theoretically using the 1D dynamic simulator GENTRANS, and experimentally combined with MS. In all configurations studied, the sample was uniformly distributed throughout the channel before power application, and driving electrodes were used as microchannel ends. In the first part, previously obtained experimental results from carrier-free systems are compared to simulation results, and the effects of atmospheric carbon dioxide and impurities in the sample solution are examined. Simulation provided insight into the dynamics of the transport of all components under the applied electric field and revealed the formation of a pure water zone in the channel center. In the second part, the use of an IEF procedure with simple well defined amphoteric carrier components, i.e. amino acids, for concentration and fractionation of peptides was investigated. By performing simulations a qualitative description of the analyte behavior in this system was obtained. Neurotensin and [Glu1]-Fibrinopeptide B were separated by IEF in microchannels featuring a liquid lid for simple sample handling and placement of the driving electrodes. Component distributions in the channel were detected using MALDI- and nano-ESI-MS and data were in agreement with those obtained by simulation. Dynamic simulations are demonstrated to represent an effective tool to investigate the electrophoretic behavior of all components in the microchannel.

  • 36.
    Parmar, Varun
    et al.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Redeby, Theres
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Van Der Wijngaart, Wouter
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    ELECTRO-OSMOTIC FLOW THROUGH CLOSED-OPEN-CLOSED MICROCHANNELS: AN APPROACH TO HYPHENATION OF CAPILLARY ELECTROPHORESIS AND MALDI2006In: 19th IEEE International Conference on Micro Electro Mechanical Systems (IEEE MEMS 2006), IEEE conference proceedings, 2006, p. 406-409Conference paper (Refereed)
    Abstract [en]

    We suggest electro-osmotic driven flow (EOF) through closed-open-closed microchannels as a novel approach for spatial sample separation using capillary electrophoresis (CE) prior to matrix assisted laser desorption/ionization mass spectroscopy (MALDI-MS). For this purpose we built a system consisting of the series Coupling of a closed fused silica capillary for separation, a microfabricated open microcanal for future MS detection and a second closed fused silica capillary for downstream liquid collection. This work verifies the EOF transport of a peptide sample in such a system with low dispersion.

  • 37.
    Redeby, Theres
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Carr, H.
    Björk, M.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    A screening procedure for the solubilization of chloroplast membrane proteins from the marine green macroalga Ulva lactuca using RP-HPLC-MALDI-MS2006In: International Journal of Biological Macromolecules, ISSN 0141-8130, E-ISSN 1879-0003, Vol. 39, no 1-3, p. 29-36Article in journal (Refereed)
    Abstract [en]

    A protocol for purification and analysis of chloroplast membrane proteins in the green macroalga Ulva lactuca has been developed, including reversed phase high performance liquid chromatography (RP-HPLC) and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Five different solvents were evaluated for extraction of membrane proteins by three methods. The highest protein yield was achieved when proteins were extracted directly from the chloroplasts using the solvent hexafluoroisopropanol. A range of proteins of increasing hydrophobicity was separated by HPLC. Analysis of both HPLC fractions and non-separated samples by MALDI-TOF-MS revealed proteins with molecular weights spanning between 1 and 376 kDa.

  • 38.
    Redeby, Theres
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Membrane protein and peptide sample handling for MS analysis using a structured MALDI target2005In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Analytical and bioanalyltical chemistry, Vol. 381, no 1, p. 225-232Article in journal (Refereed)
    Abstract [en]

    Different sample handling methods for hydrophobic proteins and peptides were evaluated in association with the utilization of a structured matrix-assisted laser/desorption ionization (MALDI) target for increased sensitivity. The fluorinated organic solvent hexafluoroisopropanol (HFIP) was used for the solubilization of both the full-length protein bacteriorhodopsin (BR) and a cyanogen bromide digest thereof, and compared to the performance of the non-ionic detergents octyl-beta-D-glucopyranoside (OG), dodecyl-beta-D-maltoside (DM), and Triton X-100. A concentrating effect was seen when using the structured MALDI plate for BR dissolved in all the different detergents, of which OG generated the best-quality spectra for the full-length integral membrane protein as well as for the hydrophobic peptides. However, the uneven analyte distribution obtained with the detergent preparations required selective and thus time-consuming acquisition of spectra. When instead HFIP was used as sample solvent, a tenfold increase in sensitivity was achieved for full-length BR. Addition of acids to the HFIP-solubilized sample, or to the MALDI matrix solution, improved the signals for a few of the peptides, while degrading the spectra of others. Consequently, the addition of acid could be used as a complementary sample preparation method for hydrophobic peptides. On-target washing to remove contaminants (e.g., salt) was performed, and a recrystallization protocol for signal improvement specifically suited for hydrophobic peptides is described. Results from digestion and solubilization in different micro centrifuge tubes were examined to determine the influence of different materials on the possible sample loss due to wall adhesion. Studies of sample solution storage times suggest immediate analysis after solubilization to obtain best results.

  • 39.
    Redeby, Theres
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Roeraade, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Simple fabrication of a structured matrix-assisted laser desorption/ionization target coating for increased sensitivity in mass spectrometric analysis of membrane proteins2004In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 18, no 10, p. 1161-1166Article in journal (Refereed)
    Abstract [en]

    A new prestructured target plate for matrix-assisted laser desorption/ionization (MALDI) was developed specifically for hydrophobic integral membrane proteins. This sample support contains predefined concentrating sample spots with a focusing effect on droplets with a high content of hexafluoroisopropanol (HFIP). This fluorinated organic solvent is advantageous for solubilizing hydrophobic proteins that are not soluble in water or the organic solvents normally used in sample preparation protocols for MALDI-MS. The prestructured plate was constructed by coating a regular steel plate with a thin layer of a silicone polymer, leaving sample spots of bare steel. Fabrication of the concentrating silicone structure was fast and very straightforward, without expensive or complicated equipment. Removing the layer, and thus regenerating the steel plate, was done by a simple washing procedure. The application and cleaning procedure are not constrained by a particular design of sample support or to any specific brand of mass spectrometer. When using the prestructured MALDI plate with HFIP as the sample solvent for 17 pmol of a cyanogen bromide digest of the highly hydrophobic membrane protein bacteriorhodopsin, an improved focusing effect and an increase of more than five-fold in average sensitivity were observed, compared with a regular steel target. Experimental results show a two-fold increase in average sensitivity when the new prestructured target plate was used, compared with a commercially available concentrating support

  • 40.
    Roeraade, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Stjernström, Mårten
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Litborn, Erik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Lindberg, Ulf
    Uppsala Universitet.
    Nanochemistry and nanoseparations of biomolecules1996In: microTAS, Special issue - Analytical methods & instrumentation, p. 26-30Article in journal (Refereed)
  • 41.
    Rojas, Orlando J.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Macakova, Lubica
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Blomberg, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Claesson, Per Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Fluorosurfactant self-assembly at solid/liquid interfaces2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 21, p. 8085-8095Article in journal (Refereed)
    Abstract [en]

    Fluorosurfactants have some unique properties that are advantageously used in a range of applications. Their solutions are commonly in contact with solid surfaces onto which the molecules adsorb. Despite this, the adsorption behavior of fluorosurfactants at solid/liquid interfaces is not sufficiently understood, and there is a need for more information. In this study we focus on cationic fluorosurfactant adsorption on negatively charged hydrophilic surfaces, especially with respect to the adsorbed layer structure, long-range interactions, and adhesion forces. To this end we combined results obtained from bimorph and interferometric surface force instruments and ellipsometry techniques. The initial adsorption to the oppositely charged surfaces occurs due to the electrostatic attraction between the charged headgroups and the surface. Further adsorption, driven by hydrophobic interactions, occurs readily as the surfactant concentration is increased. Surface force and ellipsometric experiments indicate that the surfactants self-assemble in the form of bilayer aggregates. The thickness of the bilayer aggregates was found to be consistent with the molecular structure. Further, ellipsometric measurements indicate that no complete bilayers were formed but rather that bilayer aggregates were present on the surface even at concentrations well above the cmc. Surface force data for low fluorosurfactant concentrations demonstrate that upon compression the bilayer aggregates assembled on the isolated surfaces are transformed, and as a result monolayer structures build up between the surfaces in contact. The force required to attain bilayer-bilayer contact increases with the surfactant bulk concentration due to an increase in the repulsive double-layer force. The force required to drive out surfactant molecules to achieve monolayer-monolayer contact also increases with surfactant concentration. Above the cmc some additional aggregates are present on top of the bilayer aggregates coating the surface. The adhesion found between the monolayer aggregates is an order of magnitude larger than between the bilayer aggregates. However, it is an order of magnitude lower than the corresponding value for Langmuir-Blodgett monolayer films of similar fluorosurfactants.

  • 42.
    Rokhas, Maria Khihon
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Mikkonen, Saara
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Beyer, J.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    CE analysis of single wood cells performing hydrolysis and preconcentration in open microchannels2014In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 35, no 2-3, p. 450-457Article in journal (Refereed)
    Abstract [en]

    In the present work, monosaccharides from pulp samples and single wood fibers were analyzed with CE, using indirect detection due to the lack of chromophores on the monosaccharides. The hydrolysis degradation of cellulose and hemicellulose into monosaccharides was performed using TFA, either in bulk scale or in microscale. In the microscale, one single wood fiber was hydrolyzed in an open microchannel manufactured on a silicon microchip with the dimensions 50 μm × 50 μm (length 1 or 3 cm). The low monosaccharide amounts derived from a single fiber implied that a preconcentration step was necessary to increase the detectability. Thus, an electromigration preconcentration of the hydrolyzed samples was performed within the microchannel, which resulted in a significantly enhanced signal intensity of the monosaccharides. In addition to the experimental study, computer simulations were performed regarding the preconcentration step of monosaccharides. The results from these simulations correlated well with the experimental results.

  • 43.
    Romson, Joakim
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Simple and environmentally friendly fabrication of superhydrophobic alkyl ketene dimer coated MALDI concentration plates2017In: Journal of the American Society for Mass Spectrometry, ISSN 1044-0305, E-ISSN 1879-1123, Vol. 28, no 8, p. 1733-1736Article in journal (Refereed)
    Abstract [en]

    Here we present a method to manufacture peptide-concentrating MALDI-plates with alkyl ketene dimer (AKD) as a new superhydrophobic coating. The fabrication of the hydrophobic plates included application of AKD by airbrush, and negative contact printing to generate the concentration sites. Deposited sample droplets were contained within the prestructured sites, and self-adjusted onto the site if slightly misplaced. No AKD contamination was observed, and the plates could easily be cleaned and regenerated. The S/N values for four model peptides was about twice as high compared with a standard steel plate and a commercial concentration plate.

  • 44. Sjodahl, J
    et al.
    Emmer, A
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Karlstam, B
    Vincent, J
    Roeraade, J
    Separation of proteolytic enzymes originating from Antarctic krill (Euphausia superba) by capillary electrophoresis1998In: JOURNAL OF CHROMATOGRAPHY B, ISSN 0378-4347, Vol. 705, no 2, p. 231-241Article in journal (Refereed)
  • 45. Sjodahl, J.
    et al.
    Emmer, Åsa
    KTH, Superseded Departments, Chemistry.
    Vincent, J.
    Roeraade, Johan
    KTH, Superseded Departments, Chemistry.
    Characterization of proteinases from Antarctic krill (Euphausia superba)2002In: Protein Expression and Purification, ISSN 1046-5928, E-ISSN 1096-0279, Vol. 26, no 1, p. 153-161Article in journal (Refereed)
    Abstract [en]

    Fractions of three trypsin-like proteinases, TL I, TL II, and TL III, a chymotrypsin-like proteinase, CL, two carboxypeptidase A enzymes, CPA I and CPA II and two carboxypeptidase B enzymes. CPB I and CPB II, from Antarctic krill (Euphausia superba) have been characterized with respect to purity by the means of capillary electrophoresis, CE, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The masses of the trypsin-like and chymotrypsin-like proteinases were determined to be 25,020, 25,070, 25,060. and 26,260 Da for TL I, TL II, TL III, and CL, respectively. The masses of the CPA enzymes are likely 23,170 and 23,260 Da. whereas the CPB enzyme masses likely are 33,730 and 33,900 Da, The degradation efficiency and cleavage pattern of the trypsin-like proteinases were studied with native myoglobin as a model substrate using CE, MALDI-TOF-MS, and nanoelectrospray mass spectrometry (nESI-MS). The degradation efficiency of the trypsin-like proteinases was found to be approximately 12 and 60 times higher compared to bovine trypsin at 37 degreesC and 1-3 degreesC, respectively. All three fractions of trypsin-like proteinases showed a carboxypeptidase activity in combination with their trypsin activity.

  • 46. Sjödahl, J.
    et al.
    Melin, J.
    Griss, P.
    Emmer, Åsa
    KTH, Superseded Departments, Chemistry.
    Stemme, Göran
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Roeraade, Johan
    KTH, Superseded Departments, Chemistry.
    Characterization of micromachined hollow tips for two-dimensional nanoelectrospray mass spectrometry2003In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 17, no 4, p. 337-341Article in journal (Refereed)
    Abstract [en]

    In this work an improved design of chip-based nanoelectrospray nozzles is reported. Two-dimensional matrices of out-of-plane 10 mum i.d. silicon dioxide tips with a tapered shape were manufactured using deep reactive ion etching technology. Using a peptide sample, six micromachined tips and six commercially pulled silica capillary tips were compared employing an ion trap mass spectrometer. At a flow rate of 100 nL/min, the detectability obtained was approximately the same for the two types of tips. The relative standard deviation of the signal-to-noise ratio for the peptides between six different tips was on average 22% for the micromachined tips and 45% for the pulled capillary tips. The usefulness of the micromachined tips for analysis of non-covalent protein-ligand complexes was demonstrated by the analysis of a sample of RNase A and cytidine 2'-monophosphate. In another test, analyzing a tryptic digest of 1 pmol/muL cytochrome C, 18 peptides corresponding to a 82% sequence coverage were detected. Using MS/MS, the whole sequence of an 11 amino acid cytochrome C fragment was obtained. Computer simulations were performed on the shape and magnitude of the electrical field around micromachined and pulled capillary tips. To reach the threshold electric field density at the tip apex required to initiate an electrospray, a higher electrospray voltage was needed for the chip-based tips compared with pulled capillary tips. This is due to the influence of the chip base.

  • 47.
    Springer, Valeria
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. INQUISUR (UNS-CONICET), Argentina.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ek, Patrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Lista, Adriana G.
    INQUISUR (UNS-CONICET), Argentina.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Capillary Electrophoretic Determination of Fluoroquinolones in Bovine Milk Followed by Off-Line MALDI-TOF-MS Analysis2015In: Chromatographia, ISSN 0009-5893, E-ISSN 1612-1112, Vol. 78, no 3-4, p. 285-290Article in journal (Refereed)
    Abstract [en]

    A novel appro ach for the determination of ciprofloxacin, norfloxacin and ofloxacin by capillary electrophoresis and off-line capillary electrophoresis-matrix-assisted laser desorption/ionization-time of flight-mass spectrometry coupling for the confirmation of analyte identities is presented. A polymer capillary coating was proposed with the aim to minimize suppression of the MS signal caused by the CE solution components. The fluoroquinolones were successfully separated and determined by CE-UV followed by fractionation onto a MALDI plate and off-line MS characterization. Full-cream and low-fat milk samples were used to illustrate that the proposed method represents an efficient alternative for fluoroquinolone antibiotics determination in milk.

  • 48.
    Springer, Valeria
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ek, Patrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Lista, Adriana G.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Determination of fluoroquinolones in bovine milk samples using a pipette-tip SPE step based on multiwalled carbon nanotubes prior to CE separation2014In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 37, no 1-2, p. 158-164Article in journal (Refereed)
    Abstract [en]

    A simple CE-UV method was developed for the simultaneous determination of ciprofloxacin, norfloxacin, and ofloxacin in milk samples. The optimum separation was obtained using a 20 mM ammonium dihydrogenphosphate solution with 2 mM cetyltrimethylammonium bromide at pH 3.0 as the BGE. Satisfactory resolution for structurally very similar analytes, like norfloxacin and ciprofloxacin, was achieved without including any organic solvent. Milk samples were prepared using a simple/extraction procedure based on acidic protein precipitation followed by an SPE step using only 5 mg of multiwalled carbon nanotubes as the sorbent material. The LODs for the three compounds were between 7.5 and 11.6 g/L and the RSDs for the peak areas were between 2.6 and 4.9%. The complete method was applied to spiked real milk samples with satisfactory recoveries for all analytes (84-106%).

  • 49.
    Welander, Hedvig
    et al.
    Uppsala Universitet.
    Wiberg, Henning
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Lannfelt, Lars
    Uppsala Universitet.
    Ingelsson, Martin
    Uppsala Universitet.
    Bergström, Joakim
    Uppsala Universitet.
    Histidine 50 is a crucial residue for alpha-synuclein aggregation induced by lipid peroxidation-derived aldehydes2012In: Free Radical Biology & Medicine, ISSN 0891-5849, E-ISSN 1873-4596, Vol. 53, no Suppl 1, p. S248-S249Article in journal (Refereed)
  • 50.
    Wiberg, Henning
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Ek, Patrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Pettersson, Frida Ekholm
    Lannfelt, Lars
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Roeraade, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Separation and characterization of aggregated species of amyloid-beta peptides2010In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 397, no 6, p. 2357-2366Article in journal (Refereed)
    Abstract [en]

    We have investigated the use of isoelectric focusing and immunodetection for the separation of low molecular weight species of amyloid-beta (A beta) peptides from their aggregates. From solutions of A beta(1-40) or A beta(1-42) monomeric peptides, low molecular weight material appeared at a pI value of ca. 5, while the presence of aggregates was detected as bands, observed at a pI of 6-6.5. The formation of A beta aggregates (protofibrils) was verified by a sandwich ELISA, employing the protofibril conformation-selective antibody mAb158. In order to study the aggregation behavior when using a mixture of the monomers, we utilized the IEF separation combined with Western blot using two polyclonal antisera, selective for A beta(1-40) and A beta(1-42), respectively. We conclude that both monomers were incorporated in the aggregates. In a further study of the mixed aggregates, we used the protofibril conformation-selective antibody mAb158 for immunoprecipitation, followed by nanoelectrospray mass spectrometry (IP-MS). This showed that the A beta(1-42) peptide is incorporated in the aggregate in a significantly larger proportion than its relative presence in the original monomer composition. IP-MS with mAb158 was also performed, and compared to IP-MS with the A beta-selective antibody mAb1C3, where a monomeric A beta(1-16) peptide was added to the protofibril preparation. A beta(1-16) is known for its poor aggregation propensity, and acted therefore as a selectivity marker. The results obtained confirmed the protofibril conformation selectivity of mAb158.

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