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- Liljegren, Gustav, 1973-
(författare)
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Development and Investigations of Novel Sample Preparation Techniques : Electrochemical Extraction and Evaluation of Miniaturized Analytical Devices Coupled to Mass Spectrometry
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different sample preparation steps prior to a detection method are often essential in analytical chemistry. In this thesis, both static extractions and on-line coupled solid-phase extractions have been studied in combination with different detection techniques. Aspects of performing sample preparations in miniaturized analytical devices and the development of poly(dimethylsiloxane) (PDMS) microchips are discussed. Polypyrrole was also evaluated as an electrochemically controllable stationary phase for solid-phase microextraction (SPME) and solid-phase extraction (SPE).The first part of this thesis describes the extraction of an organic compound from a very complex solid matrix utilizing the pressurized-fluid extraction (PFE) technique. The presented results show that PFE is easily optimized and enables rapid extractions and extracts relatively free from interferences.An integrated three-electrode device, which enabled electrochemical (EC) SPME under potential control, was developed. With this device, both anions and cations could be extracted employing two types of polypyrrole films. Planar micro band electrodes positioned at the end of a capillary were also used to electrochemically extract and detect anions in a miniaturized flow system. Different analyte concentrations and preconcentration times were examined, and good linear correlations were found between the extraction time and the detection response. The on-line coupling of a thin layer EC cell, with a polypyrrole coated working electrode, to different mass spectrometric (MS) techniques is also described and evaluated. The results show that EC-SPE, employing polypyrrole as stationary phase, can be used as a preconcentration step prior to detection.In addition, this thesis describes the development and on-line coupling of a microelectrode array equipped PDMS microchip with an integrated graphite electrospray emitter to electrospray ionization (ESI) MS. The system enabled short transfer times and an EC conversion efficiency of 30% at a flow rate of 0.5 μL/min. The on-line EC/ESI-MS experiments were significantly simplified using a wireless Bluetooth battery-powered EC instrument.
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| 2. |
- Liljegren, Gustav, et al.
(författare)
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On-line coupling of a microelectrode array equipped poly(dimethylsiloxane) microchip with an integrated graphite electrospray emitter for electrospray ionisation mass spectrometry
- 2005
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Ingår i: Lab on a Chip. - : Royal Society of Chemistry (RSC). - 1473-0197 .- 1473-0189. ; :5, s. 1008-1016
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Tidskriftsartikel (refereegranskat)abstract
- A novel method for the manufacturing of microchips for on-chip combinations of electrochemistry (EC) and sheathless electrospray ionisation mass spectrometry (ESI-MS) is described. The technique, which does not require access to clean-room facilities, is based on the incorporation of an array of gold microcoil electrodes into a poly(dimethylsiloxane) (PDMS) microflow channel equipped with an integrated graphite based sheathless ESI emitter. Electrochemical measurements, which were employed to determine the electroactive area of the electrodes and to test the microchips, show that the manufacturing process was reproducible and that the important interelectrode distance in the electrochemical cell could to be adequately controlled. The EC-ESI-MS device was evaluated based on the ESI-MS detection of the oxidation products of dopamine. The results demonstrate that the present on-chip approach enables full potentiostatic control of the electrochemical cell and the attainment of very short transfer times between the electrochemical cell and the electrospray emitter. The transfer times were 0.6 and 1.2 s for flow rates of 1.0 and 0.5 uL min-1, respectively, while the electrochemical conversion efficiency of the electrochemical cell was found to be 30% at a flow rate of 0.5 uL min-1. To decouple the electrochemical cell from the ESI-MS high voltage and to increase the user-friendliness, the on-line electrochemistry-ESI-MS experiments were performed using a wireless Bluetooth battery-powered instrument with the chip floating at the potential induced by the ESI high voltage. The described on-chip EC-ESI-MS device can be used for fundamental electrochemical investigations as well as for applications based on the use of electrochemically controlled sample pretreatment, preconcentration and ionisation steps prior to ESI-MS.
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| 6. |
- Liljegren, Gustav, et al.
(författare)
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On-line electrochemically controlled solid-phase extraction interfaced to electrospray and inductively coupled plasma mass spectrometry
- 2005
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; :130, s. 1358-1368
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemically controlled solid-phase extractions of anions were interfaced on-line to electrospray mass spectrometry (ESI-MS) and inductively coupled plasma mass spectrometry (ICP-MS), using polypyrrole coated electrodes and a thin-layer electrochemical (EC) flow cell. The results indicate that electrochemically controlled solid-phase extraction (EC-SPE) can be used as a versatile potential controlled sample preparation technique for a range of anions and that the properties of the polypyrrole coatings can be modified by altering the electrodeposition conditions. In the present study, the influence of interfering anions (i.e., fluoride and sulfate), and the anion used during the electropolymerisation, on the bromide extraction recovery was investigated for EC-SPE interfaced to ICP-MS. The results of these experiments show that the interference due to the presence of similar concentrations of sulfate can be reduced when using a polypyrrole coating electropolymerised in the presence of bromide ions. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements were also used to study the morphology of the coatings, as well as the variations in the film thickness within the coatings. The effect of different desorption techniques on the bromide preconcentration factor in the ICP-MS on-line flow system was also examined. Stopped-flow desorption was found to give rise to significantly increased preconcentration factors in comparison with desorptions in flowing solutions. While the desorption efficiency depends on the type of desorption electrolyte (the electrolyte in which the desorption takes place), due to the competing influx of cations, the influence of the pH on the switching charge of the polypyrrole coating was found to be small, at constant ionic strength. To study the applicability of the EC-SPE technique with respect to real samples, investigations were also made with tap water samples spiked with different bromide concentrations. The results of these experiments, which were carried out using a modified thin-layer EC flow cell allowing in situ polymerisation of polypyrrole yielding a polymer plug covering the cross section of the channel, demonstrate that 3 uM concentrations of bromide could be detected in the tap water sample. This demonstrates that the extraction technique allows extractions of low concentrations of ions in the presence of significantly higher concentrations of other similar ions. The fact that the extraction and desorption steps are electrochemically controlled makes EC-SPE particularly well suited for inclusion in miniaturised lab-on-a-chip systems.
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| 10. |
- Pettersson Dahlin, Andreas, et al.
(författare)
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Capillary electrophoresis coupled to mass spectrometry from a polymer modified poly(dimethylsiloxane) microchip with an integrated graphite electrospray tip
- 2005
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 130:2, s. 193-199
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid capillary-poly(dimethysiloxane) (PDMS) microchips with integrated electrospray ionization (ESI) tips were directly fabricated by casting PDMS in a mould. The shapes of the emitter tips were drilled into the mould, which produced highly reproducible three-dimensional tips. Due to the fabrication method of the microfluidic devices, no sealing was necessary and it was possible to produce a perfect channel modified by PolyE-323, an aliphatic polyamine coating agent. A variety of different coating procedures were also evaluated for the outside of the emitter tip. Dusting graphite on a thin unpolymerised PDMS layer followed by polymerisation was proven to be the most suitable procedure. The emitter tips showed excellent electrochemical properties and durabilities. The coating of the emitter was eventually passivated, but not lost, and could be regenerated by electrochemical means. The excellent electrochemical stability was further confirmed in long term electrospray experiments, in which the emitter sprayed continuously for more than 180 h. The PolyE-323 was found suitable for systems that integrate rigid fused silica and soft PDMS technology, since it simply could be applied successfully to both materials. The spray stability was confirmed from the recording of a total ion chromatogram in which the electrospray current exhibited a relative standard deviation of 3.9% for a 30 min run. CE-ESI-MS separations of peptides were carried out within 2 min using the hybrid PDMS chip resulting in similar efficiencies as for fused silica capillaries of the same length and thus with no measurable band broadening effects, originating from the PDMS emitter.
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