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Mass Spectrometry with Electrospray Ionization from an Adjustable Gap
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
2008 (English)Licentiate 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.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , v, 36 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:24
Keyword [en]
Electrospray ionization, mass spectrometry, nanoelectrospray, ESI, MS, chip, emitter, gap, liquid bridge, nozzle, peptides
National Category
Analytical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4747ISBN: 978-91-7178-926-6 (print)OAI: oai:DiVA.org:kth-4747DiVA: diva2:13758
Presentation
2008-05-29, E2, KTH, Lindstedtsvägen 3, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101108Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2010-11-08Bibliographically approved
List of papers
1. Electrospray Ionization from a Gap with Adjustable Width
Open this publication in new window or tab >>Electrospray Ionization from a Gap with Adjustable Width
2006 (English)In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 20, no 21, 3176-3182 p.Article in journal (Refereed) Published
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.

Keyword
article, electrospray mass spectrometry, equipment, equipment design, evaluation, instrumentation, methodology, microfluidic analysis, reproducibility, sensitivity and specificity
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-8437 (URN)10.1002/rcm.2710 (DOI)000241627000003 ()2-s2.0-33750325735 (Scopus ID)
Note
QC 20100913Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2012-02-24Bibliographically approved
2. Electrospray Ionization from an Adjustable Gap between two Silicon Chips
Open this publication in new window or tab >>Electrospray Ionization from an Adjustable Gap between two Silicon Chips
Show others...
2009 (English)In: Journal of Mass Spectrometry, ISSN 1076-5174, E-ISSN 1096-9888, Vol. 44, no 2, 171-181 p.Article in journal (Refereed) Published
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.

Keyword
Adjustable gap, Chip, Electrospray ionization, Emitter, Mass spectrometry, Nozzle
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-8438 (URN)10.1002/jms.1478 (DOI)000264013300002 ()18946877 (PubMedID)2-s2.0-59949093565 (Scopus ID)
Note
QC 20100913. Uppdaterad från Manuskript till Artikel (20100913)Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2010-11-12Bibliographically approved

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