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Improved mass accuracy in MALDI-TOF-MS analysis
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Mass spectrometry (MS) is an important tool in analytical chemistry today, particularly in the field of proteomics where identification of proteins is the central activity. The focus in this thesis has been to improve the mass accuracy of MS-analyses in order to improve the possibility for unambiguous identification of proteins.

In paper I a new peak picking algorithm has been developed for Matrix Assisted Laser Desorption/Ionization - Time of Flight - Mass Spectrometry (MALDI-TOF-MS). The new algorithm is based on the assumption that two sets of ions are formed during the ionisation, and that these two sets have different Gaussian-distributed velocity profiles. The algorithm then deconvolutes the spectral peak into two Gaussian distributions, were the narrower of the two distributions is utilized for peak picking. The two-Gaussian peak picking algorithm proved to be especially useful when dealing with weak, distorted peaks.

In paper II a novel chip-based target for MALDI analysis is described. The target features pairs of 50x50 μm anchors in close proximity. Each anchor within a pair could be individually addressed with different sample solutions. Each pair could then be irradiated with the MALDI laser, which allowed ionization to take place on separated anchors simultaneously. This made it possible for us to calibrate analytes with calibration standards that where physically separated from the analyte, but ionized simultaneously. The use of new chip-based MALDI target resulted in a 2-fold reduction of relative mass errors. We could also report a significant reduction of ion suppression. The small size of the anchors provided a good platform for efficient utilization of sample. This resulted in a detection limit of ca. 1.5 attomole of angiotensin I at a S/N of 22:1.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 44 p.
Keyword [en]
Analytical chemistry, MALDI, mass spectrometry, mass accuracy, peak picking, ion formation, proteins, peptides, chip, sample handling, sensitivity.
Keyword [sv]
Analytisk kemi
National Category
Analytical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-313ISBN: 91-7178-017-3 (print)OAI: oai:DiVA.org:kth-313DiVA: diva2:8893
Presentation
2005-05-06, K2, Teknikringen 28, Stockholm, 10:00
Supervisors
Note
QC 20101206Available from: 2005-07-18 Created: 2005-07-18 Last updated: 2010-12-06Bibliographically approved
List of papers
1. Improved method for peak picking in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
Open this publication in new window or tab >>Improved method for peak picking in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
2004 (English)In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 18, no 11, 1208-1212 p.Article in journal (Refereed) Published
Abstract [en]

A method for peak picking for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is described. The method is based on the assumption that two sets of ions are formed during the ionization stage, which have Gaussian distributions but different velocity profiles. This gives rise to a certain degree of peak skewness. Our algorithm deconvolutes the peak and utilizes the fast velocity, bulk ion distribution for peak picking. Evaluation of the performance of the new method was conducted using peptide peaks from a bovine serum albumin (BSA) digest, and compared with the commercial peak-picking algorithms Centroid and SNAP. When using the new two-Gaussian algorithm, for strong signals the mass accuracy was equal to or marginally better than the results obtained from the commercial algorithms. However, for weak, distorted peaks, considerable improvement in both mass accuracy and precision was obtained. This improvement should be particularly useful in proteomics, where a lack of signal strength is often encountered when dealing with weakly expressed proteins. Finally, since the new peak-picking method uses information from the entire signal, no adjustments of parameters related to peak height have to be made, which simplifies its practical use.

Keyword
desorption ionization, calibration method, proteomics, maldi, resolution, dynamics, velocity, profile, ions, ms
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-23445 (URN)10.1002/rcm.1467 (DOI)000221655000005 ()2-s2.0-2542537695 (Scopus ID)
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved
2. Chip with twin anchors for reduced ion suppression and improved mass accuracy in MALDI-TOF mass spectrometry
Open this publication in new window or tab >>Chip with twin anchors for reduced ion suppression and improved mass accuracy in MALDI-TOF mass spectrometry
Show others...
2005 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 77, no 3, 827-832 p.Article in journal (Refereed) Published
Abstract [en]

A new sample target for matrix-assisted laser desorption/ionization mass spectrometry is described. The target consists of pairs of elevated hydrophilic anchor surfaces, positioned in proximity onto a microchip. The anchors are used to obtain separate preparations of sample and external standard, while both anchor surfaces are irradiated simultaneously by the laser pulse. Using a standard, based on six peptides, a 2-fold improvement in mass accuracy is observed. Also, ion suppression is significantly reduced. With a one peptide calibration standard, 22 tryptic fragments from a BSA digest are detected using the twin-anchor concept, whereas only 14 fragments are detected when the sample and standard are laser-ablated as a mixture from a conventional anchor target. A volume of similar to30 pL of sample solution of angiotensin I is transferred to the anchor surface, under a thin layer of a perfluorocarbon, to prevent a concentration bias due to evaporation. With this arrangement, a detection limit of 1.5 amol was achieved with a signal-to-noise ratio of 22:1.

Keyword
assisted-laser-desorption/ionization, sample support, ms, sensitivity, proteins, dna, resolution, silicon
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-14499 (URN)10.1021/ac0400966 (DOI)000226759000022 ()2-s2.0-13344284560 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved

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