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  • 1.
    Amirkhani, Ardeshir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Heldin, Eva
    Markides, Karin E.
    Bergquist, Jonas
    Quantitation of tryptophan, kynurenine and kynurenic acid in human plasma by capillary liquid chromatography - electrospray2002In: Journal of Chromatography B, Vol. 780, no 2, p. 381-387Article in journal (Refereed)
  • 2.
    Amirkhani, Ardeshir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Rajda, Cecilia
    Arvidsson, Björn
    Bencsik, Krisztina
    Boda, Krisztina
    Seres, Erika
    Markides, Karin E.
    Vecsei, Laszlo
    Bergquist, Jonas
    Beta-interferon effects the tryptophan metabolism in the plasma of multiple sclerosis patientsManuscript (Other academic)
  • 3.
    Amirkhani, Ardeshir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Rajda, Cecilia
    Arvidsson, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Bencsik, Krisztina
    Boda, Krisztina
    Seres, Erika
    Markides, Karin E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Vecsei, Laszlo
    Bergquist, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Interferon-beta affects the tryptophan metabolism in multiple sclerosis patients2005In: European Journal of Neurology, ISSN 1351-5101, E-ISSN 1468-1331, Vol. 12, no 8, p. 625-631Article in journal (Refereed)
    Abstract [en]

    Tryptophan and its metabolites are of great interest in understanding the pathogenesis of multiple sclerosis (MS). The total levels of tryptophan and its metabolites, kynurenine and kynurenic acid were determined in plasma by capillary liquid chromatography electrospray ionisation tandem mass spectrometry. This is the first report of the plasma levels of these analytes in healthy controls and relapsing-remitting MS patients receiving long-term and acute interferon-beta (IFN-beta) treatment. Twenty-four hours post-administration increased kynurenine levels (first IFN MS versus healthy, P = 0.042) and kynurenine/tryptophan ratio (K/T; first IFN MS versus healthy, P =0.027; first IFN MS versus long-term IFN MS, P = 0.036) were found. The long-term IFN MS group had higher K/T ratios at 4 and 12 h post-administration (P = 0.015 and 0.009, respectively). The increase of K/T ratio in the first IFN MS group indicate an induction of the enzyme indolamine-2,3-dioxygenase (IDO), as reported earlier in experimental allergic encephalomyelitis. As IDO is participating in both inflammatory and neurodegenerative processes, further knowledge of its involvement in the pathogenesis of MS is of great importance.

  • 4. Bazoti, Fotini N.
    et al.
    Tsarbopoulos, Anthony
    Markides, Karin E.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Bergquist, Jonas
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Study of the non-covalent interaction between amyloid-b-peptide and melatonin using electrospray ionization mass spectrometry2005In: Journal of Mass Spectrometry, no 40, p. 182-192Article in journal (Refereed)
    Abstract [en]

    Oxidative stress and unregulated immune response are believed to play a key role in the processes inherent to Alzheimer's disease (AD). The fact that free radicals can result in neurodegeneration suggests that actions against reactive oxygen species may be beneficial in treating and preventing AD. In the light of the suggested link between oxidative stress and AD, it is proposed that antioxidants and, even more, endogenous antioxidants may offer a therapeutic regime for protection against the risk of this disease. For this reason, the formation of non-covalent complexes between amyloid-b-peptide (Ab) or its oxidized forms and melatonin was studied by quadrupole and Fourier transform ion cyclotron resonance electrospray ionization mass spectrometry. The stability of the non-covalent complex was examined under several experimental conditions, such as orifice voltage, pH, presence of organic modifier, concentration and time. Two different digestion protocols combined with mass spectrometric analysis of the resulting peptide fragments were employed in order to locate the binding site of melatonin in Ab.

  • 5.
    Bergström, Sara K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Edenwall, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Lavén, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Velikyan, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Organic Chemistry.
    Långström, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Organic Chemistry.
    Markides, Karin E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Polyamine deactivation of integrated poly(dimethylsiloxane) structures investigated by radionuclide imaging and capillary electrophoresis experiments2005In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 77, no 3, p. 938-942Article in journal (Refereed)
    Abstract [en]

    The poly(dimethylsiloxane) (PDMS) material provides a number of advantageous features, such as flexibility, elasticity, and transparency, making it useful in integrated analytical systems. Hard fused-silica capillary structures and soft PDMS channels can easily be combined by a tight fit, which offers many alternatives for structure combinations. PDMS and fused silica are in different ways prone to adsorption of low levels of organic compounds. The need for modification of the inner wall surface of PDMS channels may often be necessary, and in this paper, we describe an easy and effective method using the amine-containing polymer PolyE-323 to deactivate both fused-silica and PDMS surfaces. The adsorption of selected peptides to untreated surfaces was compared to PolyE-323-modified surfaces, using both radionuclide imaging and capillary electrophoresis experiments. The polyamine modification displayed a substantially reduced adsorption of three hydrophobic test peptides compared to the native PDMS surface. Filling and storage of aqueous solution were also possible in PolyE-323-modified PDMS channels. In addition, hybrid microstructures of fused silica and PDMS could simultaneously be deactivated in one simple coating procedure.

  • 6.
    Bergström, Sara K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    On-line coupling of microdialysis to packed capillary column liquid chromatography-tandem mass spectrometry demonstrated by measurement of free concentrations of ropivacaine and metabolite from spiked plasma samples2002In: Journal of chromatography. B, ISSN 1570-0232, E-ISSN 1873-376X, Vol. 775, no 1, p. 79-87Article in journal (Refereed)
    Abstract [en]

    An on-line coupling of microdialysis to a packed capillary column switching liquid chromatographic system (0.2 mm I.D.) and mass spectrometric detection was developed. The microdialysates were collected in the loop of the first of three valves, coupled in direct series. A deuterated internal standard was added on-line by the middle valve and the third valve operated both a pre-column, for desalting of the physiological buffer used in the sampling procedure, and a separation column. The on-line system was used to study free concentrations of ropivacaine and its metabolite (PPX) in human plasma samples. The analytes were detected by electrospray ionization in a tandem mass spectrometer operating in multiple reaction monitoring mode. The free fractions of ropivacaine (200 nM total concentration) and PPX (20 nM total concentration) in spiked plasma samples were 12±3 and 47±5% (±standard deviation for day-to-day variations, n=3), respectively.

  • 7.
    Dahlin, Andreas P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Bergström, Sara K.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Andrén, Per E.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmaceutical Biosciences, MMS, Medical Mass Spectrometry.
    Markides, Karin E.
    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.
    Poly(dimethylsiloxane)-Based Microchip for Two-Dimensional Solid-Phase Extraction-Capillary Electrophoresis with an Integrated Electrospray Emitter Tip2005In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 77, no 16, p. 5356-5363Article in journal (Refereed)
    Abstract [en]

    A microchip in poly(dimethylsiloxane) (PDMS) for in-line solid-phase extraction-capillary electrophoresis-electrospray ionization-time-of-flight mass spectrometry (SPE-CE-ESI-TOF-MS) has been developed and evaluated. The chip was fabricated in a novel one-step procedure where mixed PDMS was cast over steel wires in a mold. The removed wires defined 50-um cylindrical channels. Fused-silica capillaries were inserted into the structure in a tight fit connection. The inner walls of the inserted fused-silica capillaries and the PDMS microchip channels were modified with a positively charged polymer, PolyE-323. The chip was fabricated in a two-level cross design. The channel at the lower level was packed with 5-um hyper-cross-linked polystyrene beads acting as a SPE medium used for desalting. The upper level channel acted as a CE channel and ended in an integrated emitter tip coated with conducting graphite powder to facilitate the electrical contact for sheathless ESI. An overpressure continuously provided fresh CE electrolyte independently of the flows in the different levels. Further studies were carried out in order to investigate the electrophoretic and flow rate properties of the chip. Finally, six-peptide mixtures, in different concentrations, dissolved in physiological salt solution was injected, desalted, separated, and sprayed into the mass spectrometer for analysis with a limit of detection in femtomole levels.

  • 8.
    Isaac, Giorgis
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Bylund, Dan
    Månsson, Jan-Eric
    Markides, Karin E.
    Bergquist, Jonas
    Analysis of Phosphatidylcholine and Sphingomyelin Molecular Species From Brain Extracts Using Capillary Liquid Chromatography Electrospray Ionization Mass Spectrometry2003In: Journal of Neuroscience Methods, ISSN 0165-0270, Vol. 128, no 1-2, p. 111-119Article in journal (Refereed)
  • 9.
    Isaac, Giorgis
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Waldebäck, Monica
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Eriksson, Ulla
    Odham, Göran
    Markides, Karin E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Total Lipid Extraction of Homogenized and Intact Lean Fish Muscles Using Pressurized Fluid Extraction and Batch Extraction Technique2005In: Journal of Agricultural and Food Chemistry, ISSN 0021-8561, E-ISSN 1520-5118, Vol. 53, no 14, p. 5506-5512Article in journal (Refereed)
    Abstract [en]

    The reliability and efficiency of pressurized fluid extraction (PFE) technique for the extraction of total lipid content from cod and the effect of sample treatment on the extraction efficiency have been evaluated. The results were compared with two liquid-liquid extraction methods, traditional and modified methods according to Jensen. Optimum conditions were found to be with 2-propanol/n-hexane (65:35, v/v) as a first and n-hexane/diethyl ether (90:10, v/v) as a second solvent, 115 oC, and 10 min of static time. PFE extracts were cleaned up using the same procedure as in the methods according to Jensen. When total lipid yields obtained from homogenized cod muscle using PFE were compared yields obtained with original and modified Jensen methods, PFE gave significantly higher yields, ~10% higher (t test, P < 0.05). Infrared and NMR spectroscopy suggested that the additional material that inflates the gravimetric results is rather homogeneus and is primarily consists of phospholipid with headgroups of inositidic and/or glycosidic nature. The comparative study demonstrated that PFE is an alternative suitable technique to extract total lipid content from homogenized cod (lean fish) and herring (fat fish) muscle showing a precision comparable to that obtained with the traditional and modified Jensen methods. Despite the necessary cleanup step, PFE showed important advantages in the solvent consumption was cut by ~50% and automated extraction was possible.

  • 10.
    Johannesson, Nina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Wetterhall, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    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.
    Monomer surface modifications for rapid peptide analysis by capillary electrphoresis and capillary electrochromatography coupled to electrospray ionization mass spectrometry2004In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 25, no 6, p. 809-816Article in journal (Refereed)
    Abstract [en]

    In this study, positively charged alkylaminosilyl monomers were used to modify the inner surface of fused silica capillaries, which subsequently were employed in capillary electrophoresis (CE) and capillary electrochromatography (CEC). The obtained surfaces yield a reversed electroosmotic flow (EOF) and have varying carbon chain lengths, that interact with the analytes and give chromatographic retention. The coating procedure is very simple and fast. The performance of the modified capillaries was evaluated regarding pH influence on EOF and chromatographic interactions. The experiments were conducted with UV and mass spectrometry (MS) and applied to the separation of various neuropeptides. The derivatized surfaces showed a linear (R2 ∼0.99) pH dependence with isoelectric points (pI) at 8.6–8.8. Rapid separations of peptide standards and a protein digest with efficiencies as high as 5×105 plates/m were performed.

  • 11.
    Koivisto, Pernilla
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Bergström, Sara K.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Determination of the free concentration of ropivacaine in plasma by packed capillary liquid chromatography: A comparison of ultrafiltration and microdialysis as sample preparation methods2001In: Journal of Microcolumn Separations, ISSN 1040-7685, E-ISSN 1520-667X, Vol. 13, no 5, p. 197-201Article in journal (Refereed)
    Abstract [en]

    In this study, ultrafiltration and microdialysis have been compared as sample preparation methods to separate the free fraction of ropivacaine from the protein bound in 150 μL plasma. A liquid chromatographic system with packed capillary columns (0.2 mm internal diameter) was used to enhance sensitivity when analyzing the small sample volumes obtained after the ultrafiltration and the microdialysis. The microdialysis was performed with probes of our own construction, and to save analysis time, the microdialysis sampling was coupled on-line to the liquid chromatographic system. The reduction of back pressure in the microdialysis outlet tube and in the injector was found to be essential. The free fraction obtained with each method was equivalent: both gave a free fraction of 6%.

  • 12.
    Lavén, Martin
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Appel, L.
    Moulder, Robert
    Tyrefors, Niklas
    Markides, Karin E.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Långström, Bengt
    Determination of flumazenil in human plasma by liquid chromatography - electrospray ionisation tandem mass spectrometry2004In: Journal of Chromatography B, no 808, p. 221-227Article in journal (Refereed)
    Abstract [en]

    A liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS) method was developed to determine unlabelled flumazenil (Ro 15-1788) in human plasma in (11 C)flumazenil positron emission tomagraphy (PET) studies.

    N-Methyl tri-deuterated flumazenil was used as an internal standard. The analyte and internal standard were extracted from plasma samples using solid-phase extraction, with a recovery of 78%. This was determined through the convenience of radioactivity measurements of 11 C-labelled flumazenil. The evaporated and reconstituted eluate was analysed by LC-ESI-MS/MS. The calibration curve was linear over the tested concentration range of 0.05-0.5 nM (15-150 pg/ml) with a correlation coefficient, R 2, of 0.998 +- 0.001. A high precision was achieved, with mean intra-assay and inter-assay relative standard deviations of at most 6 and 7%, respectively. The accuracy of the method ranged from 95 to 104%. As a proof of concept, the validated method was applied in the determination of flumazenil in plasma from two healthy volunteers participating in a PET study with three repeated investigations. A bolus-infusion protocol was used to achieve a constant concentration level of flumazenil. The average plasma concentrations ranged from 0.11 and 0.19 nM and all measurements were within the calibration standard range. The flumazenil concentrations were relatively constant within each scan and the average intra-scan precision was 15%.

  • 13.
    Lavén, Martin
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Markides, Karin E.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Långström, Bengt
    Analysis of microsomal metabolic stability using high-flow-rate extraction coupled to capillary liquid chromatography-mass spectrometry2004In: Journal of Chromatography B, no 806, p. 119-126Article in journal (Refereed)
    Abstract [en]

    A method described for on-line high-speed extraction of microsomal samples and analysis by capillary liquid chromatography - mass spectrometry (LC-MS) for the determination of metabolic stability in connection with the development of positron emission tomography (PET) tracers. the method allowed direct injections of large sample volumes at a fast extraction rate, providing a gain in both sensitivity and sample preparation time. The calibration curve of the test compound flumazenil (Ro 15-1788) was linear in the concentration range of 1-150 nM, with a correlation coefficient exceeding 0.999. The accuracy of the method ranged from 98 to 101%. A high precision was obtained, with mean intra-assay and inter-assay relative standard deviations of at most 1.4 and 1.5%, respectively, for quality control (QC) samples. The extraction efficiency was determined to be 99.4%, the total recovery 96% and the carryover to <0.23%. Extractions were performed in a concentration interval of 30-300 nM without any sign of column overload. The method was successfully used for determining the microsomal metabolic stability of flumazenil. As a result, the described analysis system is currently used for metabolic screening of PET tracer candidates in our laboratory.

  • 14.
    Lavén, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Wallenborg, Susanne
    Velikyan, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Organic Chemistry.
    Bergström, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Djodjic, Majda
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Ljung, Jenny
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Berglund, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Edenwall, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Långström, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Organic Chemistry.
    Radionuclide Imaging of Miniaturized Chemical Analysis Systems2004In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 76, no 23, p. 7102-7108Article in journal (Refereed)
    Abstract [en]

    We propose radionuclide imaging as a valuable tool for the study of molecular interactions in miniaturized systems for chemical analysis. Sensitive and quantitative imaging can be performed with compounds labeled with short-lived positron-emitting radionuclides, such as C-11 and Ga-68, within selected parts of the system. Radionuclide imaging is not restricted to transparent materials since the relatively energetic positrons can penetrate high optical density materials. Experimentally, a radiotracer is introduced into the object of study, which is subsequently placed on a phosphor storage plate. After exposure, the plate is scanned with a laser and a digital, quantitative image can be reconstituted. To demonstrate the concept, three types of microstructures suited for integration in chemical analysis systems were imaged with C-11- and Ga-68-labeled tracers. The influence of factors such as geometry of the object and type of radionuclide on resolution and sensitivity was investigated. The resolution ranged from 0.9 to 2.7 mm (fwhm). Measuring low amounts of radioactivity in the three structures, 2-20 Bq could be detected, which corresponded to 2.3-500 amol or 2.4-110 pM tracer. The imaging approach was applied to study analyte concentration and sample dilution effects on the performance of a capillary extraction column integrated in an automated LC-ESI-MS system. The utility of the technique was further illustrated by imaging of microchannels in a zeonor plastic compact disk and in a poly(dimethylsiloxane) material for the study of nonspecific peptide adsorption.

  • 15.
    Liljegren, Gustav
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry.
    Pettersson, Jean
    Markides, Karin E.
    Nyholm, Leif
    Electrochemical solid-phase microextraction of anions and cations using polypyrrole coatings and an integrated three-electrode device2002In: The Analyst, ISSN 0003-2654, Vol. 127, no 5, p. 591-597Article in journal (Refereed)
  • 16.
    Moberg, My
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Markides, Karin E.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Bylund, Dan
    Multi-parameter investigation of tandem mass spectrometry in a linear ion trap using response surface modelling2005In: Journal of Mass Spectrometry, no 40, p. 317-324Article in journal (Refereed)
    Abstract [en]

    The feasibility of experimental design in combination with subsequent response surface modelling was illustrated for the prediction and interpretation of tandem mass spectrometric (MS/MS) fragmentation data using a linear quadrupole ion trap under various experimental conditions. The instrumental parameters included were (i) the pressure of the collision gas, (ii) the collision energy, (iii) the fill time of the linear ion trap and (iv) the scan rate. The spectral intensity and width of five fragment ions of the doubly charged neuro-active peptide bombesin were used for evaluation, and all experiments were performed so as to resemble the results obtained from a liquid chromatographic peak. The reported results show how fairly simple mathematical tools can be utilized sucessfully to describe fundamental mechanisms associated with multiple collisional activation and collision-induced dissociation processes without an extensively controlled experimental environment. Most beneficial, using the suggested approach, is the ability to study interaction (synergistic) effects between various parameters. As we realized from the results, many interaction effects are indeed significant. For example, the effect on the signal intensity of different collision gas pressure settings is strongly dependent on the settings of the other parameters. The described approach can easily be adopted for optimization purposes of any MS/MS experiment.

  • 17.
    Moberg, My
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Nilsson, Eva M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Holmström, Sara J. M.
    Lundström, Ulla S.
    Pettersson, Jean
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Fingerprinting metal-containing biomolecules after reductive displacement of iron by gallium and subsequent column-switched LC-ICPMS analysis applied on siderophores2004In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 76, no 9, p. 2618-2622Article in journal (Refereed)
    Abstract [en]

    Column-switching liquid chromatography followed by low-resolution ICPMS was evaluated as a tool for speciation analysis of metal-containing biomolecules. The strategy was applied on siderophores, strong iron chelators of low molecular weight (M(w) < 1500). Prior to the LC-ICPMS analysis, reductive displacement of iron by gallium was performed using ascorbate as the reducing agent to increase the sensitivity. Different experimental conditions during the exchange reaction were tested using ferrichrysin and ferrichrome for evaluation. A reaction time of 30 min and a pH of 3.9 gave an exchange yield of 27 and 83% for ferrichrysin and ferrichrome, respectively. A gradient elution profile was also developed to separate gallium-chelated siderophores on a PGC column. Detection limits for standard solutions of ferrichrysin and ferrichrome in the low-nanomolar range were obtained by monitoring the gallium-69 isotope. The combined use of LC-ICPMS and LC-ESI-MS/MS was also evaluated as a tool to identify unknown metal complexes, here siderophores, in field soil solution samples.

  • 18. Nilsson, Marie-Louise
    et al.
    Waldebäck, Monica
    Liljegren, Gustav
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry.
    Kylin, Henrik
    Markides, Karin E.
    Pressurized-fluid extraction of chlorinated paraffins from the biodegradable fraction of source-separated household waste2001In: Fresenius Journal of Analytical Chemistry, ISSN 0937-0633, Vol. 370, no 7, p. 913-918Article in journal (Refereed)
  • 19.
    Nilsson, Sara L.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Bylund, Dan
    Jörntén-Karlsson, Magnus
    Petersson, Patrik
    Markides, Karin E.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    A chemometric study of active parameters and their interaction effects in a nebulized sheath-liquid electrospray interface for capillary electrophoresis - mass spectrometry2004In: Electrophoresis, no 25, p. 2100-2107Article in journal (Refereed)
    Abstract [en]

    A chemometrics approach has been used for evaluating the effect of four experimental parameters when coupling capillary electrophoresis (CE) to electrospray ionization-mass spectrometry (ESI-MS). Electrospray voltage, sheath-liquid flow rate, nebulizing gas flow rate, and spray needle position in respect to the MS orifice were varied according to a full factorial design. In addition to main effects, two interaction effects could be identified as significant when measuring the peak intensity of the analytes, from a sample mixture containing peptides and pharmaceuticals. The first interaction effects, between the nebulizing gas flow rate and the sheath-liquid flow rate, and the second interaction effect, between the nebulizing gas flow rate and the spray poisition, could further explain the impact that these variables have on the spray performance. The number of theoretical plates and the baseline noise were also measured. The sheath-liquid flow was found to significantly affect the separation efficiency, while the noise level mainly was controlled by the nebulizing gas flow. The same factorial design was also used for a CE capillary with lower internal diameter (ID) and the effects of the same variables were compared on those capillaries using equal injection volume for both capillaries. Similar trends were obtained in both capillaries but capillary ID was shown to be a significant variable when evaluating both capillaries in a single model. It was found that a capillary with 25 um ID provided improved CE-MS performance over than corresponding 50 um ID capillary. Enhanced sensitivity was obtained using the narrow-bore capillary, and at lower sheath-liquid flow rat the 25 um ID capillary also gave rise to more efficient peaks.

  • 20.
    Pettersson, Andreas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Amirkhani, Ardeshir
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Arvidsson, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    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 feasibility study of solid supported enhanced microdialysis2004In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 76, no 6, p. 1678-1682Article in journal (Refereed)
    Abstract [en]

    For the first time, a solid supported enhanced microdialysis methodology for analysis of neuropeptides is described. The microdialysis samples were, in this study, subsequently collected in fractions, dissolved from the solid particles, dried, and resolved in a formic acid buffer in order to make them suitable for capillary liquid chromatography-mass spectrometry. Different microdialysis flow profiles were evaluated where air-gapped continuous flow was considered most suitable for the solid supported microdialysis mode. Six endogenous neuropeptides were initially used to investigate the feasibility of this enhanced microdialysis methodology. The improved relative recovery obtained from the solid supported enhanced microdialysis was varying from no effect to 10 times higher as compared to ordinary microdialysis. The most efficient enrichment was obtained for luteinizing hormone releasing hormone, which was the largest but also the most hydrophilic of the peptides. In contrast, no significant difference in recovery was observed for Leu-enkephalin being the smallest and the most hydrophobic peptide tested. These results indicate an increased flux and selective uptake of hydrophilic peptides across the membrane and enrichment on the particles in solid supported microdialysis.

  • 21. Pihlström, Tuija
    et al.
    Isaac, Giorgis
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry, Analytical Chemistry.
    Waldebäck, Monica
    Österdahl, Bengt-Göran
    Markides, Karin E.
    Pressurized Fluid Extraction (PFE) as an Alternative General Method for the Determination of Pesticide Residues in Rape Seed2002In: The Analyst, ISSN 0003-2654, Vol. 127, no 4, p. 554-559Article in journal (Refereed)
  • 22.
    Ramström, Margareta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Hagman, Charlotte
    Tsybin, Youri O.
    Markides, Karin E.
    Håkansson, Per
    Salehi, Albert
    Lundquist, Ingmar
    Håkanson, Rolf
    Bergquist, Jonas
    A novel mass spectrometric approach to the analysis of hormonal peptides in extracts of mouse pancreatic islets2003In: European Journal of Biochemistry, ISSN 0014-2956, Vol. 270, no 15, p. 3146-3152Article in journal (Refereed)
  • 23.
    Ramström, Margareta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Ivonin, Igor
    Johansson, Anders
    Askmark, Håkan
    Markides, Karin E.
    Zubarev, Roman
    Håkansson, Per
    Aquilonius, Sten-Magnus
    Bergquist, Jonas
    Cerebrospinal fluid protein patterns in neurodegenerative disease revealed by liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry2004In: Proteomics, Vol. 4, no 12, p. 4010-4018Article in journal (Refereed)
  • 24.
    Ramström, Margareta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Palmblad, Magnus
    Markides, Karin E.
    Håkansson, Per
    Bergquist, Jonas
    Protein identification in cerebrospinal fluid using packed capillary liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry2003In: Proteomics, ISSN 1615-9853, Vol. 3, no 2, p. 184-190Article in journal (Refereed)
  • 25.
    Sandberg, Anna
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    Heldin, Eva
    Lasalocid adsorbed on porous graphitic carbon as a chiral selector, in capillary liquid chromatography1998In: Journal of Chromatography A, Vol. 828, no 1-2, p. 149-156Article in journal (Refereed)
  • 26.
    Svedberg, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry.
    Pettersson, Andreas
    Nilsson, Stefan
    Nyholm, Leif
    Nikolajeff, Fredrik
    Bergquist, Jonas
    Markides, Karin E.
    Sheathless electrospray from polymer microchips2003In: Analytical Chemistry, Vol. 75, no 15, p. 3934-3940Article in journal (Refereed)
  • 27.
    Törnkvist, Anna
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    Nyholm, Leif
    Chromatographic behavior of oxidized porous graphitic carbon columnsManuscript (Other academic)
  • 28.
    Törnkvist, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Sjöberg, Per J. R.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
    Markides, Karin E.
    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.
    Analysis of catecholamines and related substances using porous graphitic carbon as separation media in liquid chromatography-tandem mass spectrometry2004In: Journal of Chromotography B, Vol. 801, no 2, p. 323-329Article in journal (Refereed)
    Abstract [en]

    Capillary porous graphitic carbon (PGC) columns have been utilized for separation of several catecholamines and related compounds (i.e. l-tyrosine, l-DOPA, 3-O-methyl-DOPA, dopamine, 3,4-dihydroxy-phenyl-acetic acid (DOPAC), homovanillic acid, noradrenaline, vanillomandelic acid and adrenaline) on-line with electrospray ionization tandem mass spectrometry (ESI–MS/MS). The use of a mobile phase without ion-pairing agents and with high content of organic modifier facilitated the coupling to the selective and sensitive mass spectrometric detection. Minimum detectable sample concentration (MDC sample) for noradrenaline, dopamine and l-tyrosine in a standard solution was estimated to 3, 10 and 30 nM, respectively (3 S/N corresponds to MDQ for l-tyrosine of approximately 8×10−14 mol). The developed strategy was applied for analysis of brain tissue, i.e. a substantia nigra (ns) sample.

  • 29.
    Törnkvist, Anna
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry, Analytical Chemistry.
    Sjöberg, Per J. R.
    Markides, Karin E.
    Heldin, Eva
    Use of an adsorbed chiral selector in capillary LC-MS2002In: Chirality, Vol. 14, no 8, p. 653-658Article in journal (Refereed)
  • 30.
    Wetterhall, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry.
    Klett, Oliver
    Markides, Karin E.
    Nyholm, Leif
    Bergquist, Jonas
    A comparison of the electrochemical stabilities of metal, polymer and graphite coated nanospray emitters2003In: The Analyst, ISSN 0003-2654, Vol. 128, no 6, p. 728-733Article in journal (Refereed)
  • 31.
    Wetterhall, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry.
    Palmblad, Magnus
    Håkansson, Per
    Markides, Karin E.
    Bergquist, Jonas
    Rapid analysis of tryptically digested cerebrospinal fluid using capillary electrophoresis-electrospray ionization-Fourier transform ion cyclotron resonance-mass spectrometry2002In: Journal of Proteome Research, ISSN 1535-3893, Vol. 1, no 4, p. 361-366Article in journal (Refereed)
  • 32.
    Zuberovic, Aida
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Ullsten, Sara
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Hellman, Ulf
    Markides, Karin E.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Bergquist, Jonas
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Analytisk kemi.
    Capillary electrophoresis off-line matrix-assisted laser desorption/ionisation mass spectrometry of intact and digested proteins using cationic-coated capillaries2004In: Rapid Communications in Mass Spectrometry, no 18, p. 2946-2952Article in journal (Refereed)
    Abstract [en]

    Capillary electrophoresis (CE) was coupled off-line with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) for the analysis of proteins and peptides. CE fractions were collected directly on a matrix-coated MALDI target, using a sheath-flow interface. Protein adsorption during CE separations was prevented by coating the capillaries with the physically adsorbed, cationic polymer PolyE-323. The CE/MALDI-MS system was used for the analysis of model proteins and peptides at physiological pH as well as analysis of proteins in tear fluid. Moreover, tryptic on-target digestion of the collected protein fractions, with subsequent MALDI-MS and MS/MS peptide analysis, was demonstrated.

1 - 32 of 32
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