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  • 101.
    Wetterhall, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Nilsson, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Bergquist, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    A conductive polymeric material used for nanospray needle and low-flow sheathless electrospray ionization applications2002In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 74, no 1, p. 239-245Article in journal (Refereed)
    Abstract [en]

    A conductive polypropylene/graphite mixture is used for the production of polymeric nanospray needle emitters and as a coating on fused-silica capillaries that are used for sheathless electrospray ionization (ESI). The described production of these polymeric nanospray needle emitters and sheathless ESI contacts is exceptionally easy and at a very low cost. The described polymeric nanospray emitters have shown excellent features regarding their chemical inertness and spray performance. The long-term stability of the nanospray needles exceeds 24 h of continuous use. Furthermore, the resistance to electrical discharges, which is one of the factors that often limits the lifetime of metal coated tips, has proven to be outstanding. A voltage of up to 5 kV could be applied without loss of spray performance. The use of polypropylene emitters offers a number of desirable features, as compared to silica based emitters. Among these features are mechanical flexibility and simplified regeneration of the nanospray needle. Continuous nanospray of peptides and proteins in conjunction with orthogonal time-of-flight mass spectrometry are shown with signal relative standard deviations of 5%. In addition, the polypropylene/graphite mixture has also been applied as the conductive contact for sheathless ESI in fast capillary electrophoresis separations.

  • 102. Wisniewski, Jacek R.
    et al.
    Gaugaz, Fabienne Z.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Fast and Sensitive Total Protein and Peptide Assays for Proteomic Analysis2015In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 87, no 8, p. 4110-4116Article in journal (Refereed)
    Abstract [en]

    The determination of total protein content is one of the most frequent analytical tasks in biochemistry and molecular biology. Here we evaluate measurements of tryptophan fluorescence (WF) for total protein determination in whole tissue lysates and for peptide quantification in protein digests. We demonstrate that the fluorescence spectrometry of tryptophan offers a simple, sensitive, and direct method for protein and peptide assays. The WF assay is fully compatible with SDS and other solutes that are commonly used for lysis of tissue and cells. We found that the content of tryptophan varies only a little between mouse tissues (1.16 +/- 0.08% of total amino acids) and is similar in human cells (1.19 +/- 0.06%). Therefore, free tryptophan can be used as a universal standard. We show that the assay can be carried out on a standard fluorescence spectrometer with cuvettes as well as in a 96-well format using a plate reader. The method is particularly suitable for determination of peptide content in diluted samples. Notably, the whole sample can be recovered after the measurement.

  • 103.
    Zettersten, Camilla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry.
    Co, Michelle
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry.
    Wende, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry.
    Turner, Charlotta
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Sjöberg, Per J. R.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry.
    Identification and Characterization of Polyphenolic Antioxidants Using On-Line Liquid Chromatography, Electrochemistry, and Electrospray Ionization Tandem Mass Spectrometry2009In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 81, no 21, p. 8968-8977Article in journal (Refereed)
    Abstract [en]

    It is demonstrated that electrochemistry (EC) coupled to liquid chromatography (LC) and electrospray ionization tandem mass spectrometry (LC/EC/ESI-MS/MS) can be used to rapidly obtain information about the antioxidant activity (i.e., oxidation potential) and capacity (i.e., amount) of polyphenolic compounds, including catechin, kaempferol, resveratrol, quercetin, and quercetin glucosides. The described on-line LC/EC/ESI-MS/MS method facilitates the detection and characterization of individual antioxidants based on a combination of the obtained m/z values for the antioxidants and their oxidation products, the potential dependences for the ion intensities, and correlations between the retention times in the LC, EC, and MS chromatograms. As these results provide patterns that can be used in rapid screening for antioxidants in complex samples, the method should be a valuable complement to chemical assays commonly used to determine the total antioxidant capacity of samples. It is shown that the antioxidant capacity for a mixture of polyphenolic compounds depends on the redox potential employed in the evaluation, and this should consequently be taken into account when comparing results from different total antioxidant capacity assays. It is also demonstrated that the inherent antioxidant capacities of phenolic compounds increase with an increasing number of hydroxyl groups and that the potential needed to oxidize the remaining hydroxyl groups increases successively upon oxidation of the compound. Unlike chemical assays, which generally do not provide any information about the identities of the compounds on the molecular level, the present screening method can be used to identify individual antioxidants, rank compounds with respect to their ease of oxidation, and to study the antioxidant capacity at any redox potential of interest.

  • 104.
    Zettersten, Camilla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Sjöberg, Per J. R.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Oxidation of 4-chloroaniline studied by on-line electrochemistry electrospray ionization mass spectrometry2009In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 81, no 13, p. 5180-5187Article in journal (Refereed)
    Abstract [en]

    The oxidation of 4-chloroaniline (4-CA) has been studied by electrochemistry (EC) coupled on-line with electrospray ionization mass spectrometry (ESI-MS) using two electrochemical flow cells of different design. The experimental results, which generally verify previously suggested oxidation pathways for 4-CA, also indicate the presence of a so far unrecognized comproportionation reaction. The oxidation of 4-CA (m/z 128.2) was found to give rise to the formation of both an oxidized dimer, 4-[(4-chlorophenyl)imino]-2,5-cyclohexadien-1-imine (m/z 217.2) and a reduced dimer, 4-amino-4’-chlorodiphenylamine (m/z 219.2), in addition to a dimer intermediate (m/z 253.2). This unexpected formation of the reduced dimer is shown to stem from a comproportionation reaction involving 4-CA and the oxidized dimer. The presence of the latter reaction was clearly seen by comparing results obtained with two thin-layer flow cells, both with conversion efficiencies of 50% but of different design, with respect to the influence of the counter electrode reaction on the reaction at the working electrode. The experimental results demonstrate that the formation of the reduced dimer is favored by a decrease in the local pH in the flow cell and the influence of the pH on the oxidation of 4-CA was also investigated in the pH range between 2.0 and 6.0 using off-line voltammetry. It is concluded that EC/ESI-MS is a powerful tool for the study of the present type of reactions and that studies on reaction pathways are best carried out with thin-layer flow cells having conversion efficiencies smaller than 100% as this facilitates the detection of reaction intermediates. Comproportionation reactions, similar to the reaction present in the 4-CA system, can also be expected to be present during the formation of conducting polymers such as polyaniline and polypyrrole.

  • 105.
    Zhang, Jinbao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ellis, Hanna
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Yang, Lei
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Johansson, Erik M. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Vlachopoulos, Nick
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Bergquist, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Shevchenko, Denys
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Matrix-Assisted Laser Desorption/Ionization Mass Spectrometric Analysis of Poly(3,4-ethylenedioxythiophene) in Solid-State Dye-Sensitized Solar Cells: Comparison of In Situ Photoelectrochemical Polymerization in Aqueous Micellar and Organic Media2015In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 87, no 7, p. 3942-3948Article in journal (Refereed)
    Abstract [en]

    Solid-state dye-sensitized solar cells (sDSCs) are devoid of such issues as electrolyte evaporation or leakage and electrode corrosion, which are typical for traditional liquid electrolyte-based DSCs. Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most popular and efficient p-type conducting polymers that are used in sDSCs as a solid-state hole-transporting material. The most convenient way to deposit this insoluble polymer into the dye-sensitized mesoporous working electrode is in situ photoelectrochemical polymerization. Apparently, the structure and the physicochemical properties of the generated conducting polymer, which determine the photovoltaic performance of the corresponding solar cell, can be significantly affected by the preparation conditions. Therefore, a simple and fast analytical method that can reveal information on polymer chain length, possible chemical modifications, and impurities is strongly required for the rapid development of efficient solar energy-converting devices. In this contribution, we applied matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) for the analysis of PEDOT directly on sDSCs. It was found that the PEDOT generated in aqueous micellar medium possesses relatively shorter polymeric chains than the PEDOT deposited from an organic medium. Furthermore, the micellar electrolyte promotes a transformation of one of the thiophene terminal units to thiophenone. The introduction of a carbonyl group into the PEDOT molecule impedes the growth of the polymer chain and reduces the conductivity of the final polymer film. Both the simplicity of sample preparation (only application of the organic matrix onto the solar cell is needed) and the rapidity of analysis hold the promise of making MALDI MS an essential tool for the physicochemical characterization of conducting polymer-based sDSCs.

  • 106.
    Zubarev, Roman A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Radiation Sciences.
    Damirev, Plamen A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Radiation Sciences.
    Håkansson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Radiation Sciences.
    Sundqvist, Bo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Radiation Sciences.
    Approaches and Limits for Accurate Mass Characterization of Large Biomolecules1995In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 67, no 20, p. 3793-3798p. 3793-3798Article in journal (Refereed)
    Abstract [en]

    The use of the average mass for mass characterization oflarge biomolecules is examined in light of the latestachievements in mass spectrometry, and factors affectingthe accuracy of both theoretical calculation and experimentaldetermination are analyzed. It is concluded that,in practice, the accuracy of average mass measurementsis limited to f O . l Da for molecular masses below 10 000Da and to 10 ppm for masses above that value. Inherentproperties of the isotopic distributions lead to a systematicunderestimation of the average mass during the measurements.The procedure proposed earlier (Zubarev, R A.Int. J. Mass. Spectrom. Ion Processes 1991,107,17-27) in order to correct for this effect is now extended tothe case of multiply-charged ions and their use for massscale calibration. A formula is derived for the relationshipbetween mass accuracy and both the instrumental resolvingpower and molecular ion peak statistics. Monoisotopicmass measurements are recommended to be usedwhenever possible. As a complement to that, otheradditive quantities, such as the ratio of intensities of theh t is otopic peak to the monoisotopic peak, can beemployed.

  • 107.
    Zubarev, Roman A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Radiation Sciences.
    Håkansson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Radiation Sciences.
    Sundqvist, Bo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Radiation Sciences.
    Accuracy requirements for peptide characterization by monoisotopic molecular mass measurements1996In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 68, no 22, p. 4060-4063Article in journal (Refereed)
    Abstract [en]

    Accurately measured monoisotopic mass of a biomolecule can reveal its elemental and, in the case of a biopolymer, its monomer composition. In this work, the limitations of the technique were analyzed in application to peptides. For the currently available level of mass accuracy of about ±1 ppm, the mass limit for revealing the unique elemental composition of a peptide was found to be 700−800 Da, with the possibility to extend this range as the mass accuracy improves. As for the amino acid composition determination, the principal limit of 500−600 Da cannot be overcome in the general case by instrumental or methodological improvements. It is proposed that, for the peptide characterization, the molecular mass must be determined with sufficient accuracy to rule out a significant fraction of the peptides having the same nominal mass but different elemental and amino acid compositions. An accuracy of ±1 ppm was found to exclude 99% of such peptides and, therefore, ensure a high degree of confidence in peptide characterization.

  • 108.
    Ölander, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Handin, Niklas
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Artursson, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Image-based quantification of cell debris as a measure of apoptosis2019In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 91, no 9, p. 5548-5552Article in journal (Refereed)
    Abstract [en]

    Apoptosis is a controlled form of cell death that can be induced by various diseases and exogenous toxicants. Common apoptosis detection methods rely on fluorescent markers, which necessitates the use of costly reagents and time-consuming labeling procedures. Label-free methods avoid these problems, but often require specialized instruments instead. Here, we utilize apoptotic cell disintegration to develop a novel label-free detection method based on the quantification of subcellular debris particles in bright-field microscopy images. Debris counts show strong correlations with fluorescence-based annexin V staining, and can be used to study concentration-dependent and temporal apoptosis activation. The method is rapid, low-cost, and easy to apply, as the only experimental step comprises bright-field imaging of culture media samples, followed by automated image processing. The late-stage nature of the debris measurement means that the method can complement other, established apoptosis assays, and its accessibility will allow a wider community of researchers to study apoptotic cell death.

123 101 - 108 of 108
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