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  • 1.
    Ek, Patrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Mass Spectrometry with Electrospray Ionization from an Adjustable Gap2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis the fabrication and analytical evaluation of two new electrospray emitters utilized for mass spectrometry analysis is presented. The emitters are based on a new concept, where the spray orifice can be varied in size. The thesis is based on two papers.

    All present-day nanoelectrospray emitters have fixed dimensions. The range of the applicable flow rate for such an emitter is therefore rather limited and exchange of emitters may be necessary from one experiment to another. Optimization of the signal of the analyte ions is also limited to adjustments of the applied voltage or the distance between the emitter and the mass spectrometer inlet. Furthermore, clogging can occur in emitters with fixed dimensions of narrow orifice sizes. In this thesis, electrospray emitters with a variable size of the spray orifice are proposed. An open gap between two thin substrates is filled with sample solution via a liquid bridge from a capillary. Electrospray is generated at the end point of the gap, which can be varied in width.

    In Paper I, electrospray emitters fabricated in polyethylene terephthalate have been evaluated. Triangular tips are manually cut from the polymer film. The tips are mounted to form a gap between the edges of the tips. The gap wall surfaces are subjected to a hydrophilic surface treatment to increase the wetting of the gap walls.

    In Paper II, silicon electrospray chips with high precision are fabricated and evaluated. A thin beam, elevated from the bulk silicon chip is fabricated by means of deep reactive ion etching. The top surfaces of the beams of two chips act as a sample conduit when mounted in the electrospray setup. An anisotropic etching step with KOH of the intersecting <100> crystal planes results in a very sharp spray point. The emitters were given a hydrophobic surface treatment except for the hydrophilic gap walls.

    For both emitter designs, the gap width has been adjusted during the experiments without any interruption of the electrospray. For a continuously applied peptide mixture, a shift towards higher charge states and increased signal to noise ratios could be observed when decreasing the gap width. The limit of detection has been investigated and the silicon chips have been interfaced with capillary electrophoresis.

  • 2.
    Ek, Patrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    New methods for sensitive analysis with nanoelectrospray ionization mass spectrometry2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, new methods that address some current limitations in nanoelectrospray mass spectrometry (nESI-MS) analysis are presented. One of the major objectives is the potential gain in sensitivity that can be obtained when employing the proposed techniques.

    In the first part of this thesis, a new emitter, based on the generation of electrospray from a spray orifice with variable size, is presented. Electrospray is generated from an open gap between the edges of two individually mounted, pointed tips. The fabrication and evaluation of two different types of such emitters is presented; an ESI emitter fabricated from polyethylene terephtalate (Paper I), and a high-precision silicon device (Paper II). Both emitters were surface-treated in a selective way for an improved wetting of the gap and to confine the sample solution into the gap.

    In the second part of this thesis, different methods for improved sensitivity of nESI-MS analysis have been developed. In Paper III, a method for nESI-MS analysis from discrete sample volumes down to 1.5 nL is presented, using commercially available nESI needles. When analyzing attomole amounts of analyte in such a small volume of sample, an increased sensitivity was obtained, compared to when analyzing equal amounts in conventional nESI-MS analysis. To be able to analyze smaller sample volumes, needles with a narrower orifice and a higher flow resistance were needed. This triggered the development of a new method for fabrication of fused silica nESI needles (Paper IV). The fabrication is based on melting of a fused silica capillary by means of a rotating plasma, prior to pulling the capillary into a fine tip. Using the described technique, needles with sub-micrometer orifices could be fabricated. Such needles enabled the analysis of sample volumes down to 275 pL, and a further improvement of the sensitivity was obtained. In a final project (Paper V), nESI-MS was used to study the aggregation behavior of Aβ peptides, related to Alzheimer’s disease. An immunoprecipitation followed by nESI-MS was employed. This technique was also utilized to study the selectivity of the antibodies utilized.

  • 3.
    Ek, Patrik
    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.
    New Method for Fabrication of Fused Silica Emitters with Submicrometer Orifices for Nanoelectrospray Mass Spectrometry2011In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 83, no 20, p. 7771-7777Article in journal (Refereed)
    Abstract [en]

    In this paper, we describe a new method for fabrication of nanoelectrospray emitters. The needles were pulled from fused silica capillary tubing, which was melted by means of a plasma, formed by electrical discharges between two pointed platinum electrodes. A key feature of the pulling device is a rotating configuration of the electrodes, which results in an even radial heating of the capillary. The construction of the setup is straightforward, and needles with a variety of shapes can be fabricated, including orifices of submicrometer dimensions. Pulled needles with long tapered tips and an orifice of 0.5 mu m were utilized for electrospray ionization mass spectrometry (ESI-MS) of discrete sample volumes down to 275 pL. The picoliter-sized samples were transferred into the tip of the needle from a silicon microchip by aspiration. To avoid a rapid evaporation of the sample, all manipulations were performed under a cover of a fluorocarbon liquid. The limit of detection was measured to be ca. 20 attomole for insulin (chain B, oxidized).

  • 4.
    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.

  • 5.
    Ek, Patrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Sjödahl, Johan
    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 a Gap with Adjustable Width2006In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 20, no 21, p. 3176-3182Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a new concept for electrospray ionization mass spectrometry, where the sample is applied in a gap which is formed between the edges of two triangular-shaped tips. The size of the spray orifice can be changed by varying the gap width. The tips were fabricated from polyethylene terephthalate film with a thickness of 36 μm. To improve the wetting of the gap and sample confinement, the edges of the tips forming the gap were hydrophilized by means of silicon dioxide deposition. Electrospray was performed with gap widths between 1 and 36 μm and flow rates down to 75 nL/min. The gap width could be adjusted in situ during the mass spectrometry experiments and nozzle clogging could be managed by simply widening the gap. Using angiotensin I as analyte, the signal-to-noise ratio increased as the gap width was decreased, and a shift towards higher charge states was observed. The detection limit for angiotensin I was in the low nM range.

  • 6.
    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.

  • 7.
    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.

  • 8.
    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%).

  • 9.
    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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