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Novel clean-up, concentration and laser desorption/ionization strategies for mass spectrometry
Stockholm University, Faculty of Science, Department of Analytical Chemistry.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Despite valuable advantages of mass spectrometry (MS) techniques they still have drawbacks that need to be overcome, notably their sensitivity to various kinds of interfering substances and associated difficulties involved in detecting signals from analytes present in trace quantities. Thus, high quality analytical data could be acquired by improving sample pre-treatment techniques and/or ionization methods to increase ionization yields and/or avoid the generation of unwanted ions.

In the studies this thesis is based upon, a microfluidic electrocapture system capable of trapping charged proteins/polypeptides while non-charged species such as non-ionic detergents are swept out, was used to decrease the concentration of detergent in samples containing soluble and membrane associated proteins/polypeptide. Subsequent mass spectrometric analysis yielded well-resolved mass spectra of the target analytes.

In addition, it was found that solid phase extraction (SPE) sorbents such as graphitized carbon black (GCB), can efficiently assist the laser desorption ionization of small molecules without generating any interfering ions which inspired the fabrication of μ-traps and discs. Other matrix-free approaches demonstrated the utility of silicon nitride and oxidized GCB nanoparticles as versatile media for surface-assisted laser desorption ionization (SALDI) of small molecules.

In this thesis it is discussed that small molecule analytes such as Polyphenols present in red wine and quaternary protoberberine alkaloids with highly conjugated systems and acidic/permanently charged functional groups can be readily analyzed without any matrix or assisting-surface.

In summary, the microfluidic electrocapture, new laser desorption ionization methods and surfaces, as well as integrated SALDI and SPE platforms, introduced in this work extend the MS strategies allowing coverage of a wider range of samples.

Place, publisher, year, edition, pages
Stockholm: Department of Analytical Chemistry, Stockholm University , 2010. , 77 p.
Keyword [en]
Mass spectrometry, ESI-MS, SALDI-MS, Electrocapture, Sample treatment
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
URN: urn:nbn:se:su:diva-32236ISBN: 978-91-7155-981-4 (print)OAI: oai:DiVA.org:su-32236DiVA: diva2:279849
Public defence
2010-01-22, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: In PressAvailable from: 2009-12-17 Created: 2009-12-07 Last updated: 2011-08-31Bibliographically approved
List of papers
1. Matrix-free thin-layer chromatography/laser desorption ionization mass spectrometry for facile separation andidentification of medicinal alkaloids
Open this publication in new window or tab >>Matrix-free thin-layer chromatography/laser desorption ionization mass spectrometry for facile separation andidentification of medicinal alkaloids
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2009 (English)In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 23, no 23, 3655-3660 p.Article in journal (Refereed) Published
Abstract [en]

Quaternary protoberberine alkaloids belong to a pharmaceutically important class of isoquinoline alkaloids associated with bactericidal, fungicidal, insecticidal and antiviral activities. As traditional medicine gains wider acceptance, quick and robust analytical methods for the screening and analysis of plants containing these compounds attract considerable interest. Thin-layer chromatography (TLC) combined with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful technique but suffers from dilution of the TLC bands resulting in decreased sensitivity and masking of signals in the low-mass region both due to addition of matrix. This study integrates for the first time conventional silica gel TLC and laser desorption ionization mass spectrometry (LDI-MS) thus eliminating the need for any external matrix. Successful separation of berberine (Rf = 0.56) and palmatine (Rf = 0.46) from Berberis barandana including their identification by MS are demonstrated. Furthermore, a robust electrospray ionization (ESI)-MS method utilizing residual sample from TLC for quantification of berberine applying selected reaction monitoring and standard addition method is presented. The amount of berberine in the plant root prepared for the study was determined to be 0.70% (w/w). Copyright © 2009 John Wiley & Sons, Ltd.

Identifiers
urn:nbn:se:su:diva-33258 (URN)10.1002/rcm.4297 (DOI)
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
2. Matrix-less laser desorption/ionisation mass spectrometry of polyphenols in red wine
Open this publication in new window or tab >>Matrix-less laser desorption/ionisation mass spectrometry of polyphenols in red wine
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2009 (English)In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 23, no 12, 1834-1840 p.Article in journal (Refereed) Published
Abstract [en]

Matrix-assisted laser desorption/ionisation (MALDI) of small molecules is challenging and in most cases impossible due to interferences from matrix ions precluding analysis of molecules <300-500 Da. A common matrix such as ferulic acid belongs to an important class of compounds associated with antioxidant activity. If the shared phenolic structure is related to the propensity as an active MALDI matrix then it follows that direct laser desorption/ionisation should be possible for polyphenols. Indeed matrix-less laser desorption/ionisation mass spectrometry is achieved whereby the analyte functions as a matrix and was used to monitor low molecular weight compounds in wine samples. Sensitivity ranging from 0.12-87 pmol/spot was achieved for eight phenolic acids (4-coumaric, 4-hydroxybenzoic, caffeic, ferulic, gallic, protocatechuic, syringic, vanillic) and 0.02 pmol/spot for trans-resveratrol. Additionally, 4-coumaric, 4-hydroxybenzoic, caffeic, ferulic, gallic, syringic, vanillic acids and trans-resveratrol were identified in wine samples using accurate mass measurements consistent with reported profiles based on liquid chromatography (LC)/MS. Minimal sample pre-treatment make the technique potentially appropriate for fingerprinting, screening and quality control of wine samples. Copyright © 2009 John Wiley & Sons, Ltd.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-33255 (URN)10.1002/rcm.4062 (DOI)
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved
3. Screening and Quantification of Pesticides in Water Using a Dual-Function Graphitized Carbon Black Disk
Open this publication in new window or tab >>Screening and Quantification of Pesticides in Water Using a Dual-Function Graphitized Carbon Black Disk
2010 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 82, no 1, 290-296 p.Article in journal (Refereed) Published
Abstract [en]

A simple platform for combining solid phase extraction (SPE) and surface-assisted laser desorption ionization mass spectrometry (SALDI-MS) of extracted analytes, using disks prepared by embedding graphitized carbon black (GCB-4) particles in a network of polytetrafluoroethylene (PTFE), is presented. The system provides a convenient approach for rapid SALDI-MS screening of substances in aqueous samples, which can be followed by robust quantitative and/or structural analyses by liquid chromatography (LC)/MS/MS of positive samples. The extraction discs are easily transferred between gaskets where the sample extraction and desorption of selected samples is performed and the mass spectrometer. The SPE and SALDI properties of the new GCB-4 disc have been characterized for 15 pesticides with varying chemical properties, and the screening strategy has been applied to the analysis of pesticides in agricultural drainage water. Atrazine and atrazine-desethyl-2-hydroxy were detected in the sampled water by SALDI-MS screening and subsequently confirmed and quantified using LC/MS/MS.

Place, publisher, year, edition, pages
ACS, 2010
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:su:diva-32223 (URN)10.1021/ac901946b (DOI)000273265700047 ()
Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
4. SALDI-MS Signal Enhancement Using Oxidized Graphitized Carbon Black Nanoparticles
Open this publication in new window or tab >>SALDI-MS Signal Enhancement Using Oxidized Graphitized Carbon Black Nanoparticles
2009 (English)In: Journal of the American Society for Mass Spectrometry, ISSN 1044-0305, E-ISSN 1879-1123, Vol. 20, no 6, 1207-1213 p.Article in journal (Refereed) Published
Abstract [en]

The signal intensity of low-molecular-weight compounds analyzed using surface-assisted laserdesorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) was significantlyenhanced when oxidized graphitized carbon black (GCB) particles were used as the desorption/ionization surface. The surface of oxidized GCB contains more carboxylic acid groupsthan non-oxidized GCB. Carboxylic acid groups enhance the efficiency of the ionizationprocess and the desorption of more hydrophobic compounds. A common pharmaceuticalcompound, propranolol, was successfully extracted from Baltic Sea blue mussels and quantifiedusing oxidized GCB as the SALDI surface, whereas deuterated propranolol was used asthe internal standard. The calibration curve showed a wide linear dynamic range of response(0.1–20 g/mL) and good reproducibility (RSD 10%). It was not possible to detectpropranolol in Baltic Sea blue mussels when non-oxidized GCB was used as the SALDI surface.

Identifiers
urn:nbn:se:su:diva-38262 (URN)10.1016/j.jasms.2009.02.017 (DOI)000266466600036 ()
Available from: 2010-04-06 Created: 2010-04-06 Last updated: 2017-12-12Bibliographically approved
5. Silicon nitride nanoparticles for surface-assisted laser desorption/ionization of small molecules
Open this publication in new window or tab >>Silicon nitride nanoparticles for surface-assisted laser desorption/ionization of small molecules
2009 (English)In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 11, no 6, 1509-1512 p.Article in journal (Refereed) Published
Abstract [en]

Conventional matrix-assisted laser desorption/ionization mass spectrometry is limited to analyses of higher molecular weight compounds due to high background noise generated by the matrix in the lower mass region. Surface-assisted laser desorption/ionization (SALDI) mass spectrometry is an alternative solution to this problem. Nanoparticles, structured silicon surfaces and carbon allotropes are commonly used as SALDI surfaces. Here, for the first time, we demonstrate the application of silicon nitride nanoparticles as a suitable medium for laser desorption/ionization of small drug molecules.

Identifiers
urn:nbn:se:su:diva-38263 (URN)10.1007/s11051-009-9601-6 (DOI)
Available from: 2010-04-06 Created: 2010-04-06 Last updated: 2017-12-12Bibliographically approved
6. µ-trap for the SALDI-MS screening of organic compounds prior to LC/MS analysis
Open this publication in new window or tab >>µ-trap for the SALDI-MS screening of organic compounds prior to LC/MS analysis
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2008 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 80, no 14, 5515-5523 p.Article in journal (Refereed) Published
Abstract [en]

A procedure for rapidly screening and quantitatively analyzing organic molecules is presented, in which a miniaturized solid-phase extraction (SPE) cartridge containing 0.6 mg of graphitized carbon black (the GCB-mu-trap) is used for sample pretreatment. Then surface-assisted laser desorption ionization dine-of-flight mass spectrometry (SALDI-TOF-MS) screening is followed by liquid chromatography/mass spectrometry (LC/MS) for robust quantitative analysis of samples containing analytes of interest. Liquid samples with volumes up to 100 mL were extracted using the GCB-mu-trap, and SALDI screening was performed by transferring a few particles of the GCB 4 sorbent from the mu-trap onto a stainless steel plate. Analytes were then simply ionized and desorbed by irradiating the GCB 4 particles without any further pretreatment. GCB 4 was found to be an excellent surface for the SALDI analysis of small molecules, providing spectra with very clean backgrounds. The small size of the cartridge (micropipet filter tip) results in enrichment of the analytes on a small surface area, affording low SALDI-TOF-MS detection limits. Furthermore, the removal of just a few particles from the p-trap does not significantly affect the subsequent quantitative determination. This approach offers considerable reductions in analytical costs by eliminating unnecessary SPE-LC/MS analyses.

Place, publisher, year, edition, pages
ACS, 2008
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:su:diva-17512 (URN)10.1021/ac8005186 (DOI)000257598100033 ()
Available from: 2009-01-16 Created: 2009-01-16 Last updated: 2017-12-13Bibliographically approved
7. Microfluidic electrocapture-assisted mass spectrometry of membrane-associated polypeptides
Open this publication in new window or tab >>Microfluidic electrocapture-assisted mass spectrometry of membrane-associated polypeptides
2008 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 80, 7116-7120 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
ACS, 2008
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:su:diva-17511 (URN)000259199400035 ()
Available from: 2009-01-16 Created: 2009-01-16 Last updated: 2017-12-13Bibliographically approved

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