| 1. |
- Törnkvist, Anna, et al.
(författare)
-
Interference of the electrospray voltage on chromatographic separations using porous graphitic carbon columns
- 2004
-
Ingår i: Journal of Mass Spectrometry. - : Wiley. - 1076-5174 .- 1096-9888. ; 39:2, s. 216-222
-
Tidskriftsartikel (refereegranskat)abstract
- The electrospray ionization (ESI) voltage is shown to interfere with liquid chromatographic separations performed with packed porous graphitic carbon (PGC) capillary columns. This interference is ascribed to the presence of an electric field over the conductive column in the absence of an earth point between the column and the ESI emitter. The current evolved alters the chromatographic behavior of the catecholamine metabolite 3-O-methyl-DOPA significantly, as both peak splitting and a dramatic decrease in the retention time were observed. Furthermore, the response from the mass spectrometer was decreased by 33% at the same time. A related compound, tyrosine, exhibited decreased retention times but no peak splitting, whereas no shifts in the retention times (or peak splitting) were seen for the less retained dopamine and noradrenaline. When the current through the PGC column was eliminated by the use of an earth point between the column and the ESI emitter, the chromatographic behavior of the column was found to return slowly to normal after hours of equilibration with 60 : 40 (v/v) methanol-ammonium formate buffer of pH 2.9. The behavior of the PGC column with and without the earth point was found to be highly reproducible during a period of 1 month. We propose that the effect of the ESI voltage on the chromatographic behavior of the PGC column is due to associated redox reactions affecting both the PGC particles and the analytes. It is concluded that (for analytical reasons), care should be taken to ensure that no current is flowing through the chromatographic system when interfacing PGC columns, and conducting parts in general, to ESI mass spectrometry.
|
|
| 2. |
- Andersen, Jesper N, et al.
(författare)
-
Strong Phonon Replicas in Be 1 s Photoemission Spectra
- 2001
-
Ingår i: Physical Review Letters. - 1079-7114. ; 86:19, s. 4398-4401
-
Tidskriftsartikel (refereegranskat)abstract
- The Be 1s core level photoemission line from metallic Be is shown to contain unexpected internal fine structure. We argue that this fine structure is caused by intrinsic excitation of a narrow band of optical phonons in the 1s photoemission process. The general importance of the present results for high resolution core level photoemission investigations of metals is pointed out.
|
|
| 3. |
- Andersen, J. N., et al.
(författare)
-
Strong phonon replicas in Be 1s photoemission spectra
- 2001
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 86:19, s. 4398-4401
-
Tidskriftsartikel (refereegranskat)abstract
- Strong phonon replicas in Be 1s photoemission spectra were investigated. The fine structure caused by intrinsic excitation of a narrow band of optical phonons was discussed in the 1s photoemission proces. The excitations of the optical Be phonons in the photoemission process caused fine structures. It was found that the phonon replicas in Be metal were strong due to large size misfit between neutral and core-ionized Be.
|
|
| 4. |
- Bökman, C.Fredrik, et al.
(författare)
-
A Setup for the Coupling of a Thin-Layer Electrochemical Flow Cell to Electrospray Mass Spectrometry
- 2004
-
Ingår i: Analytical Chemistry. ; 76:7, s. 2017-2024
-
Tidskriftsartikel (refereegranskat)abstract
- A novel setup for the coupling of commercially available thin-layer cell to electrospray mass spectrometry (ESI-MS) which allows the elctrochemical reactions at the counter electrode to be straightforwardly separated from the flow into the mass spectrometer has been developed. In this way interferences from reaction products formed at the counter electrode can be minimized. This reduces the risk of changes in the mass spectra as a result of electrochemical reactions in the solution. The described setup also enables the working electrode to be positioned close to the electrospray (ESI) emitter without the need for a grounding point or a long transfer line between the electrochemical cell and the electrospray emitter. By decoupling the electrochemical reactions in the flow cell and those in the electrospray emitter, improved facilities for studies of electrochemical reactions are obtained through a better control of the potential of the working electrode. The setup has been used to study the oxidation of a drug (Olsalazine), which previously has been found to involve chemical follow-up reactions. It is also demonstrated that uncharged thiols can be detected in ESI-MS after spontaneous adsorption on a gold working electrode, followed by oxidative desorption to yield sulfinates or sulfonates. This adsorption and potential-controlled desorption has been used for the preconcentration of micromolar concentrations of 1-hexanethiol as well as for desalting of solutions containing micromolar concentrations of thiols. The results indicate that the present on-line coupling of an electrochemical cell to ESI-MS provides promising possibilities for sample preconcentration, matrix exchange (including desalting), and ionization of neutral compounds, such as thiols.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
- Nilsson, Stefan, et al.
(författare)
-
A simple and robust conductive graphite coating for sheathless electrospray emitters used in capillary electrophoresis/mass spectrometry
- 2001
-
Ingår i: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 15:21, s. 1997-2000
-
Tidskriftsartikel (refereegranskat)abstract
- A graphite-polyimide mixture was used as a conductive coating for sheathless electrospray emitters. The coating procedure described is simple and inexpensive compared to previously described methods. An investigation of the stability of the conductive coating carried out by electrochemical methods revealed good performances during oxidative stress. In addition, no decrease in emitter performance was seen during continuous electrospray in the positive electrospray mode for two weeks. Fast capillary electrophoresis with attomole sensitivity demonstrated the excellent performance of the described sheathless interface when used in conjunction with an orthogonal time-of-flight mass spectrometer. The overall simplicity, stability and low cost of this type of sheathless emitter make the described approach highly suitable for any on-column coupling of low flow rate separation techniques to a mass spectrometer.
|
|
| 12. |
- Nilsson, Stefan, 1972-
(författare)
-
Development of Sheathless Electrospray Mass Spectrometry and Investigations of Associated Electrochemical Processes – A Fairy Tale
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In microscale separations, such as capillary electrophoresis and -liquid chromatography, the liquid flow rates are in the order of nanoliters per second. If such flow rates are to be interfaced with a mass spectrometer (MS) using electrospray (ES) ionization, without loss of separation efficiency, each fraction of the analyte zone must remain undisturbed by the high voltage contact necessary for ES. One design that accomplishes this is the pure sheathless approach, where a thin, vapor deposited metal film covers the outside of the electrospray emitter tip. This thesis describes the development of such sheathless emitters. The lifetimes of polymer embedded gold (“fairy dust”) or graphite (“black dust”) emitters were shown to by far exceed those of previously used conductive films. In addition, the production of emitters with these coatings was substantially simplified. The increase in durability was found to be due to enhanced resistance towards the electrochemical processes associated with ES. In analogy, the reasons for the limited durability of previously used methods were correlated with their tendency to oxidize, or be mechanically removed, during electrochemical reactions. Electrochemical processes associated with the electrospray potential were also found to seriously disturb analyses in which porous graphitic carbon was used as the separation medium. A proper choice of grounding point locations eliminated these disturbances.At last, the differences regarding analytical performance of several sheathless interface configurations, used in capillary liquid chromatography, were examined. The best performance was obtained when a pure sheathless emitter with a conductive layer of polyimide and graphite was coupled to the LC column through a Teflon sleeve.
|
|
| 13. |
|
|
| 14. |
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Oscarsson, Sven, et al.
(författare)
-
Electrochemical Microcontact Printing of Thiolated Silicon Surfaces by Generation Of Reactive Thiolsulfinates/Sulfonates
- 2004
-
Ingår i: Proceedings of 7th World Biomaterials Congress, Sydney, 17-21 May, 2004.
-
Konferensbidrag (refereegranskat)abstract
- Liquid DMSO has been investigated by means of X-ray and neutron diffraction, quantum-chemical calculations and molecular dynamics (MD) simulations. A new analytical all-atom pair potential for DMSO-DMSO interactions was developed from quantum-chemical calculations and employed in the simulations. The MD-derived total structure function agrees favourably with those obtained from the X-ray and neutron diffraction experiments. An analysis of the local structure shows a rather unstructured liquid with a slight for antiparallel ordering of the S-O dipoles.
|
|
| 19. |
|
|
| 20. |
- Svedberg, Malin, et al.
(författare)
-
Sheathless Electrospary from a Polymer Microchip
- 2003
-
Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 75:15, s. 3934-3940
-
Tidskriftsartikel (refereegranskat)
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
|
|
| 24. |
|
|
