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| 3. |
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| 4. |
- Axrup, L, et al.
(författare)
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Using miniature diode array NIR spectrometers for analysing wood chips and bark samples in motion
- 2000
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Ingår i: JOURNAL OF CHEMOMETRICS. - : JOHN WILEY & SONS LTD. - 0886-9383. ; 14:5-6, s. 561-572
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Tidskriftsartikel (refereegranskat)abstract
- The chemical and physical properties of the wood chips entering the Kraft pulping process are of high interest for many different reasons. The most important one is the possibility to establish an effective and dynamic forward process control. The same is
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| 6. |
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| 7. |
- Bergström, Sara K., et al.
(författare)
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A simplified multidimensional approach for analysis of complex biological samples : on-line LC-CE-MS
- 2006
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 131:7, s. 791-798
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Tidskriftsartikel (refereegranskat)abstract
- Information on protein expression, disease biomarkers or surrogate markers and genetic disorders can nowadays be achieved from analysis of complex biological samples by liquid separation coupled to mass spectrometric (MS) detection. This paper describes fast multidimensional separation by on-line liquid chromatography (LC) and capillary electrophoresis (CE), followed by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) MS detection. This detector provides ultrahigh resolution of the detected ions, mass accuracy at the ppm-level and high sensitivity. Most of the challenge of this system lies in the development of a new interface for the on-line coupling of LC to CE. The interface developed in poly(dimethylsiloxane) provides a RSD for injection repeatability of <3.5% and surface control for unspecific binding by deactivation with a cationic polymer, PolyE-323. We have evaluated the interface, as well as the overall system, with respect to robustness and deconvolution ability. Sequence coverage for bovine serum albumin (BSA) of 93% showed a high recovery of sample in the different transfer steps through the system. The detection limit for identification is 277 ng mL−1 (or 280 nM) on average for peptides. In the future, we expect LC-CE-MS to be a novel strategy for elucidating the chemistry of biological matrices.
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| 8. |
- Bergström, Sara K, et al.
(författare)
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Development of a Poly(dimethylsiloxane) Interface for On-Line Capillary Column Liquid Chromatography : Capillary Electrophoresis Coupled to Sheathless Electrospray Ionization Time-of-Flight Mass Spectrometry
- 2003
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 75:20, s. 5461-5467
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Tidskriftsartikel (refereegranskat)abstract
- An interface in elastomeric poly(dimethylsiloxane) (PDMS) for on-line orthogonal coupling of packed capillary liquid chromatography (LC) (i.d. = 0.2 mm) with capillary electrophoresis (CE) in combination with sheathless electrospray ionization (ESI) time-of-flight mass spectrometric (TOFMS) detection is presented. The new interface has a two-level design, which in combination with a continuous CE electrolyte flow through the interface provides integrity of the LC effluent and the CE separation until an injection is desired. The transparent and flexible PDMS material was found to have a number of advantages when combined with fused silica column technology, including ease to follow the process and ease to exchange columns. By combining conventional microscale systems of LC, CE, and ESI−MS, respectively, the time scales of the individual dimensions were harmonized for optimal peak capacity per unit time. The performance of the LC−CE−TOFMS system was evaluated using peptides as model substances. A S/N of about 330 was achieved for leucine-enkephaline from a 0.5 μL LC injection of 25 μg/mL peptide standard.
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| 9. |
- Bergström, Sara K., et al.
(författare)
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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 samples
- 2002
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Ingår i: Journal of chromatography. B. - 1570-0232 .- 1873-376X. ; 775:1, s. 79-87
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Bergström, Sara K., et al.
(författare)
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Polyamine deactivation of integrated poly(dimethylsiloxane) structures investigated by radionuclide imaging and capillary electrophoresis experiments
- 2005
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 77:3, s. 938-942
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Bergström, Sara K., et al.
(författare)
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Screening of microdialysates taken before and after induced liver damage; on-line solid phase extraction-electrospray ionization-mass spectrometry
- 2006
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1120:1-2, s. 21-26
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Tidskriftsartikel (refereegranskat)abstract
- A novel method is described to follow known and unknown compounds in biological processes using microdialysis sampling and mass spectrometric detection. By implementation of internal standard, desalting/enrichment for the sample work-up, and multivariate data analysis, this methodology is a basis for future applications in early diagnosis of diseases and organ damage, as a complement to the routinely used clinical methods for biological samples. The present study includes screening without specific target analytes, of samples collected by microdialysis from liver of anaesthetized rats before and after local damage to this organ. Sample series were classified by principal component analysis, and the stimulation was identified in the chemical patterns produced by the presented analytical tool.
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| 15. |
- Dahlin, Andreas P., et al.
(författare)
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Poly(dimethylsiloxane)-Based Microchip for Two-Dimensional Solid-Phase Extraction-Capillary Electrophoresis with an Integrated Electrospray Emitter Tip
- 2005
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 77:16, s. 5356-5363
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 16. |
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| 20. |
- Juvancz, Z, et al.
(författare)
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A polymeric high resolution Pirkle-type chiral stationary phase for GC and SFC
- 1998
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Ingår i: Enantomier. - 1024-2430. ; 3:2, s. 89-94
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Tidskriftsartikel (refereegranskat)abstract
- A chiral stationary phase with a silicone backbone and substituted side chains of (S)-N-1-(1-naphthyl)-4-propyloxybenzamide substitution has been introduced for open tubular column GC and SFC. The stationary phase has a broad temperature working range 20-280 degrees C), and provides highly efficient columns (> 3000 plates/meter). One of the key interactions for selectivity is the pi-pi interaction, but the stationary phase can also be used to separate enantiomers without pi electrons. The phase can be used to separate a broad range of compounds, which is demonstrated by the separation of enantiomeric compounds having aromatic rings, amino acid and terpenic alcohol groups. This stationary phase expands the use of Pirkle phases into the field of open tubular column chromatography.
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| 21. |
- Koivisto, Pernilla, et al.
(författare)
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Determination of the free concentration of ropivacaine in plasma by packed capillary liquid chromatography : A comparison of ultrafiltration and microdialysis as sample preparation methods
- 2001
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Ingår i: Journal of Microcolumn Separations. - : Wiley. - 1040-7685 .- 1520-667X. ; 13:5, s. 197-201
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Tidskriftsartikel (refereegranskat)abstract
- 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%.
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| 22. |
- Koivisto, P., et al.
(författare)
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Separation of L-DOPA and four metabolites in plasma using a porous graphitic carbon column in capillary liquid chromatography
- 2002
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Ingår i: Chromatographia. - 0009-5893 .- 1612-1112. ; 55:1-2, s. 39-42
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Tidskriftsartikel (refereegranskat)abstract
- Porous graphitic carbon has been successfully used for the separation of L-DOPA and four metabolites (dopamine, 3,4-dihydroxy-phenyl-acetic acid, homovanillic acid and 3-O-methyl-L-DOPA) and with a volatile mobile phase of relatively high percentage organic modifier (methanol-ammonium formate pH 2.9, 60∶40, v/v). The substances were analysed in plasma. Ultrafiltration was used to remove the proteins from the sample and a coupled column system to enrich and perform on-line sample clean up. Both precolumn and separation column of i. d. 0.2 mm were packed with porous graphitic carbon.
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| 27. |
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| 28. |
- Moberg, M., et al.
(författare)
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Fingerprinting metal-containing biomolecules after reductive displacement of iron by gallium and subsequent column-switched LC-ICP-MS analysis applied on siderophore.
- 2004
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 76:9, s. 2618-2622
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Tidskriftsartikel (refereegranskat)abstract
- Column-switching liquid chromatography followed by lowresolution 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.
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| 31. |
- Nilsson, S, et al.
(författare)
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Evaluations of the stability of sheathless electrospray ionization mass spectrometry emitters using electrochemical techniques
- 2001
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 73:19, s. 4607-4616
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Tidskriftsartikel (refereegranskat)abstract
- The processes that cause the failure of sheathless electrospray ionization (ESI) emitters, based on different kinds of gold coatings on fused-silica capillaries, are described and explained. The methods chosen for this study include electrochemical methods, ICPMS analysis of the electrolytes used, SEM studies, and electrospray experiments. Generally, the failure occurs by loss of the conductive coating. It is shown that emitters with sputter-coated gold lose their coatings because of mechanical stress caused by the gas evolution accompanying water oxidation or reduction. Emitters with gold coatings on top of adhesion layers of chromium and nickel alloy withstand this mechanical stress and have excellent durability when operating as cathodes. When operating as anodes, the adhesion layer is electrochemically dissolved through the gold film, and the gold film then flakes off. It is shown that the conductive coating behaves as a cathode even in the positive electrospray mode when the magnitude of a superimposed reductive electrophoretic current exceeds that of the oxidative electrospray current. Fairy-dust coatings developed in our laboratory (see Barnidge, D. R., et al. Anal. Chem. 1999, 71, 4115-4118) by gluing gold dust onto the emitter, are unaffected by the mechanical stress due to gas evolution. When oxidized, the fairy-dust coatings show an increased surface roughness and decreased conductivities due to the formation of gold oxide. The resistance of this oxide layer is however negligible in comparison with that of the gas phase in ESI. Furthermore, since no flaking and only negligible electrochemical etching of gold was found, practically unlimited emitter lifetimes may be achieved with fairy-dust coatings.
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| 32. |
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| 33. |
- Nilsson, S. L., et al.
(författare)
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Phosphate buffers in capillary electrophoresis/mass spectrometry using atmospheric pressure photo ionization and electrospray ionization
- 2003
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Ingår i: Rapid Communication in mass spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 17:20, s. 2267-2272
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Tidskriftsartikel (refereegranskat)abstract
- Capillary electrophoresis (CE) has been combined with atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) for mass spectrometric (MS) detection. Separation conditions using potassium phosphate buffer and ammonium formate buffer have been compared for analysis of eleven pharmaceutical bases. The results showed improvements in separation efficiency and peak symmetry when phosphate buffer was used. The low flow in CE may enable utilization of these advances with MS detection. Compared with ESI, the APPI technique provided a cluster-free background. The enhanced signal-to-noise ratio in the total ion current (TIC) and the reduced spectral background indicated that the APPI process is less affected by non-volatile salts in the CE buffers. This results in a wider range of choice of CE buffers in CE/MS analysis when APPI is the ionization method.
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| 34. |
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| 35. |
- 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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| 36. |
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| 37. |
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| 38. |
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| 39. |
- Samskog, Jenny, et al.
(författare)
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On-column polymer-imbedded graphite inlet electrode for capillary electrophoresis coupled on-line with flow injection analysis in a poly(dimethylsiloxane) interface
- 2003
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Ingår i: Electrophoresis. - : Wiley. - 0173-0835 .- 1522-2683. ; 24:11, s. 1723-1729
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Tidskriftsartikel (refereegranskat)abstract
- A method for coupling an electrophoretic driven separation to a liquid flow, using conventional fused-silica capillaries and a soft polymeric interface is presented. A novel design of the electrode providing high voltage to the electrophoretic separation was also developed. The electrode consisted of a conductive polyimide/graphite imbedded coating immobilized onto the capillary electrophoresis (CE) column inlet. This integrated electrode gave the same separation performance as a commonly used platinum electrode. The on-column electrode also showed good electrochemical stability in chronoamperometric experiments. In addition, with this electrode design, the electrode position relative to the inlet end of the CE column will always be constant and well defined. The on-line flow injection analysis (FIA)-CE system was used with electrospray ionization (ESI)-time of flight (TOF)-mass spectrometry detection. The preparation of the PDMS (poly(dimethylsiloxane)) interface for FIA-CE is described in detail and used for initial tests of the on-column polymer-imbedded graphite inlet electrode. In this interface, a pressure-driven liquid flow, a make up CE electrolyte and a CE column inlet meet in a two-level cross (95 μm ID) in the PDMS structure, enabling independent flow characterization.
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| 40. |
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| 41. |
- Svantesson, E, et al.
(författare)
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A kinetic study of the self-degradation of o-carboranylalanine to nido-carboranylalan in solution
- 1999
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Ingår i: ACTA CHEMICA SCANDINAVICA. - : MUNKSGAARD INT PUBL LTD. - 0904-213X. ; 53:9, s. 731-736
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Tidskriftsartikel (refereegranskat)abstract
- The spontaneous degradation of racemic o-carboranylalanine [3-(1,2-dicarbacloso-dodecaboran(12)-1-yl)-2-aminopropanoic acid], a carborane analogue of the amino acid phenylalanine, to the corresponding diastereomeric, racemic pairs of nido-carboranylalani
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| 42. |
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| 43. |
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| 44. |
- Svedberg, M, et al.
(författare)
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Electrospray from a plastic chip
- 2001
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Ingår i: Micro Total Analysis Systems 2001, Monterey, USA. ; , s. 335-336
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Konferensbidrag (refereegranskat)
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