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Interference of the electrospray voltage on chromatographic separations using porous graphitic carbon columns
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry, Analytical Chemistry.
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2004 (English)In: Journal of Mass Spectrometry, ISSN 1076-5174, E-ISSN 1096-9888, Vol. 39, no 2, 216-222 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2004. Vol. 39, no 2, 216-222 p.
Keyword [en]
catecholamine, dopamine, electrochemistry, porous graphitic carbon, electrospray, mass spectrometry, liquid chromatography
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-91888DOI: 10.1002/jms.589OAI: oai:DiVA.org:uu-91888DiVA: diva2:164757
Available from: 2004-05-25 Created: 2004-05-25 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Development of Sheathless Electrospray Mass Spectrometry and Investigations of Associated Electrochemical Processes – A Fairy Tale
Open this publication in new window or tab >>Development of Sheathless Electrospray Mass Spectrometry and Investigations of Associated Electrochemical Processes – A Fairy Tale
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Utveckling av lågflödeselektrospray-masspektrometri samt undersökningar av associerade elektrokemiska processer – en fésaga
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 41 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 989
Keyword
Analytical chemistry, electrospray, sheathless, mass spectrometry, capillary electrophoresis, electrochemistry, chromatography, interface, fairy dust, gold, Analytisk kemi
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:uu:diva-4293 (URN)91-554-5989-7 (ISBN)
Public defence
2004-09-10, Room B 41, BMC - Uppsala Biomedical Center, Husargatan 3, Uppsala, 10:15
Opponent
Supervisors
Available from: 2004-05-25 Created: 2004-05-25Bibliographically approved
2. Aspects of Porous Graphitic Carbon as Packing Material in Capillary Liquid Chromatography
Open this publication in new window or tab >>Aspects of Porous Graphitic Carbon as Packing Material in Capillary Liquid Chromatography
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, porous graphitic carbon (PGC) has been used as packing material in packed capillary liquid chromatography. The unique chromatographic properties of PGC has been studied in some detail and applied to different analytical challenges using both electrospray ionization-mass spectrometry (ESI-MS) and ultra violet (UV) absorbance detection.

The crucial importance of disengaging the conductive PGC chromatographic separation media from the high voltage mass spectrometric interface has been shown. In the absence of a grounded point between the column and ESI emitter, a current through the column was present, and changed retention behaviors for 3-O-methyl-DOPA and tyrosine were observed. An alteration of the chromatographic properties was also seen when PGC was chemically oxidized with permanganate, possibly due to an oxidation of the few surface groups present on the PGC material.

The dynamic adsorption of the chiral selector lasalocid onto the PGC support resulted in a useful and stable chiral stationary phase. Extraordinary enantioselectivity was observed for 1-(1-naphthyl)ethylamine, and enantioseparation was also achieved for other amines, amino acids, acids and alcohols.

Finally, a new strategy for separation of small biologically active compounds in plasma and brain tissue has been developed. With PGC as stationary phase it was possible to utilize a mobile phase of high content of organic modifier, without the addition of ion-pairing agents, and still selectively separate the analytes.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 44 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 805
Keyword
Analytical chemistry, PGC, porous graphitic carbon, stationary phase, packing material, LC, liquid chromatography, miniaturized, chiral, enantiomer, ESI, electrospray ionization, mass spectrometry, polar compounds, L-DOPA, dopamine, biological samples, biological matrix, Analytisk kemi, PGC, poröst grafitiserat kol, stationärfas, packningsmaterial, LC, vätskekromatografi, miniatyriserade system, kiral, enantiomer, ESI, electrospray jonisation, mass spektrometri, polära föreningar, L-DOPA, dopmamine, biologiska prover, biologisk matris
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:uu:diva-3306 (URN)91-554-5532-8 (ISBN)
Public defence
2003-03-20, BMC, B21, Uppsala, 10:15
Opponent
Available from: 2003-02-25 Created: 2003-02-25 Last updated: 2013-06-13Bibliographically approved
3. Development of Techniques and Methods for the Quantitative Analysis of Endogenous Substances by Microcolumn Liquid Chromatography Coupled to Mass Spectrometry
Open this publication in new window or tab >>Development of Techniques and Methods for the Quantitative Analysis of Endogenous Substances by Microcolumn Liquid Chromatography Coupled to Mass Spectrometry
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Utveckling av tekniker och metoder för kvantitativ analys av endogena substanser med mikrokolonn vätskekromatografi sammankopplad med masspektrometri
Abstract [en]

Liquid chromatography-mass spectrometry (LC-MS) is a powerful technique for the analysis of endogenous compounds. The introduction of electrospray ionization (ESI) as an interface between LC and MS has contributed strongly to a trend towards miniaturization of LC, due to the possibility to perform ESI at low flow rates. In this thesis, several aspects regarding the design of miniaturized LC systems and electrospray emitters were investigated. In addition miniaturized LC-ESI-MS have been used for the qualitative and quantitative analysis of endogenous polar compounds, peptides and protein digests.

The performance of miniaturized LC-MS was compared using different electrospray emitter configurations. The results indicated that the efficiency of the LC system is rather independent of the configuration of the emitter.

The lifetime of gold-coated fused silica electrospray emitters based on vapor deposited adhesion layers of titanium were investigated. The long lifetime of the emitter facilitates the use in LC-MS experiments, exemplified LC-MS by analysis of neuropeptides.

The ESI voltage is shown to interfere with liquid chromatographic separations performed in packed porous graphitic carbon capillary column. This interference is ascribed to the presence of an electric field over the conductive column in absence of a ground point between the column and the ESI emitter.

The solid supported enhanced microdialysis for analysis of neuropeptides were compared with conventional microdialysis. The difference between the two methodologies were evaluated by LC-MS analysis of the microdialysates. The solid supported method gave in general higher relative recoveries.

Finally, a method of standard addition was developed to determine total level of tryptophan and two of its metabolites in human plasma by capillary LC-ESI tandem mass spectrometry. The method was applied in a clinical study of multiple scleroses patients treated with cytokines (IFN Beta 1a, 1b). The results show that the intervention effects the tryptophan metabolism.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 48 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 936
Keyword
Analytical chemistry, Analytisk kemi
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:uu:diva-3990 (URN)91-554-5869-6 (ISBN)
Public defence
2004-02-20, B 41, BMC, Husargatan 3 75 237, Uppsala, 10:15
Opponent
Supervisors
Available from: 2004-01-30 Created: 2004-01-30 Last updated: 2013-06-14Bibliographically approved

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