1. |
- Önnerfjord, Patrik, et al.
(author)
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Homogeneous sample preparation for automated high throughput analysis with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.
- 1999
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In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 13:5, s. 315-22
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Journal article (peer-reviewed)abstract
- This work presents a simple method for obtaining homogeneous sample surfaces in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) for the automated analysis of peptides and proteins. The sample preparation method is based on applying the sample/matrix mixture onto a pre-deposited highly diluted matrix spot. The pre-deposited crystals act as seeds for the new sample containing crystals which become much smaller in size and more evenly distributed than with conventional methods. This 'seed-layer' method was developed, optimised and compared with the dried-droplet method using peptides and proteins in the 1000-20,000 Da range. The seed-layer method increases the surface homogeneity, spot to spot reproducibility and sample washability as compared with the commonly used dried-droplet method. This methodology is applicable to alpha-cyanohydroxycinnamic acid, sinapinic acid and ferulic acid, which all form homogeneous crystal surfaces. Within-spot variation and between-spot variation was investigated using statistics at a 95% confidence level (n = 36). The statistical values were generated from more than 5000 data points collected from 500 spectra. More than 90% of the sample locations results in high intensity spectra with relatively low standard deviations (RSDs). Typically obtained data showed an RSD of 19-35% within a sample spot as well as in-between spots for proteins, and an RSD of < or = 50% for peptides. Linear calibration curves were obtained within one order of magnitude using internal calibration with a point-RSD of 3% (n = 10). The sample homogeneity allows mass spectra (average of 16 laser shots) to be obtained on each individual sample within 15 sec, whereby a 100 spot target plate can be run in 25 min. High density target plates using the seed-layer method were prepared by spotting approximately 100 picoliter droplets onto the target, resulting in sample spots < or = 500 microns in diameter using a flow-through piezo-electric micro-dispenser. By using this automated sample preparation step lower standard deviations are obtained in comparison to manually prepared samples.
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2. |
- Zubarev, Roman A., et al.
(author)
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Delayed, gas-phase ion formation in plasma desorption mass spectrometry
- 1997
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In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 11:9, s. 963-972
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Journal article (peer-reviewed)abstract
- The formation mechanisms of secondary ions from organic targets under MeV ion bombardment were studied with a high-resolution time-of-flight (TOF) mass spectrometer. Promptly formed ions Hn+, Cn+ and CnH+ were used for calibrating the TOF scale. Theoretical flight times of other ions were calculated according to the calibration curve and compared to experimentally determined values. The TOF values of non-specific low mass fragments formed via rearrangement or breaking of several bonds and/or abstraction of several atoms, agree well with the theoretical values. On the other hand, target-specific organic ions, including molecular ions of peptides, have longer TOF values than predicted by the calibration curve. Time delays of a few hundred picoseconds were found for low-mass specific fragments, and a few nanoseconds for peptide molecular ions. For protonated species and non-covalent clusters, the delays are larger than for pre-formed and radical molecular ions. Metals contained in organic samples, as contamination, also give delayed ions. For inorganic targets of LiBF4, significant delays were found for the clusters (LiF)nLi+ with n >3. A strong correlation was observed between the delay of an ion and the tailing of its kinetic energy distribution. The conclusion was made that the majority of target-specific ions are formed in the gas phase, at a distance from the target surface of the order of 1 μm.
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3. |
- Axelsson, Jan, et al.
(author)
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Electron Capture Dissociation of Substance-P using a Commercially Available Fourier Transform Ion Cyclotron Resonance Mass Spectrometer
- 1999
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In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 13:6, s. 474-477
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Journal article (peer-reviewed)abstract
- Electron capture dissociation of the peptide Substance P is reported for the first time, with an unmodified, commercially available Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. The fragmentation pattern is compared with that obtained with collisionally induced dissociation of the ions in the electrospray ion source, and note that electron capture dissociation gives a more easily interpreted spectrum, showing mainly C-fragments. With the exception of the proline residues, which require cleavage of two chemical bonds, we observe all C-fragmental we find the bias voltage of the electron gun not to be very critical.
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4. |
- Bergquist, Jonas, et al.
(author)
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Identification of catecholamines in the immune system by electrospray ionization mass spectrometry.
- 1998
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In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 12:11, s. 683-8
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Journal article (peer-reviewed)abstract
- The first evidence that catecholamines might be present in the immune system was provided by capillary electrophoresis combined with electrochemical detection. Here, we present the first structural characterization of the endogenous catecholamines isolated from human peripheral blood mononuclear cells. Dopamine, L-DOPA and norepinephrine were detected and were identified with electrospray ionization mass spectrometry by determination of the protonated molecular species of each catecholamine and their major fragments generated in the electrospray source with a nozzle-skimmer voltage method. This technique, in conjunction with accurate mass measurement, allowed us to identify in an unfractionated sample the content of catecholamines in extracted cells in a quantitative manner, with structure-specific methodology. The data unambiguously confirm our previous tentative findings, and also strengthen the importance of the regulatory function of catecholamines in the immune system and the existence of an autocrine loop, where lymphocytes may down-regulate their own activity.
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5. |
- Stolyarova, V.L, et al.
(author)
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High-temperature Mass Spectrometric Study of the Vaporization of Dysprosium Trifluoride
- 1996
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In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 10:5, s. 501-508
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Journal article (peer-reviewed)abstract
- The high-temperature Knudsen effusion method was used to study the vaporization processes and thermodynamic properties of dysprosium trifluoride in the temperature range 1280-1440 K. Data on the partial vapour pressure of DyF3 as a function of temperature and the enthalpy of sublimation of DyF3 were obtained. Using the value of the enthalpy of formation of solid DyF3, available in the literature, the enthalpy of formation of the gaseous molecule of dysprosium trifluoride and its atomization energy were calculated. At 1382 K, the partial vapour pressure of Dy2F6 over dysprosium trifluoride was obtained and the Gibbs energy of the gaseous reaction (Dy2F6)=(2DyF3) was evaluated.
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6. |
- Zubarev, Roman A., et al.
(author)
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Accurate monoisotopic mass measurements of peptides : Possibilities and limitations of high resolution time-of-flight particle desorption mass spectrometry
- 1996
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In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 10:11, s. 1386-1392
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Journal article (peer-reviewed)abstract
- The possibilities and limitations of time-of-flight particle-desorption mass spectrometry are analysed from the standpoint of accuracy of monoisotopic mass determination. For an instrument with mass reflector, typical mass accuracy was found to be ca. 20 ppm (standard deviation). The main limitation was found to be the mechanism of secondary ion production itself. A fraction of biological ions are formed in the gas phase and therefore exhibit both time delay and energy deficit. This leads to a limited resolving power and non-symmetric ion peaks. A peak shape model, taking into account gas-phase ion formation, is built and analysed, and a simple correction procedure proposed. The application of the correction has increased the mass accuracy to 12 ppm (standard deviation). It is shown that further progress cannot be achieved by a correction procedure without instrumental improvements.
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7. |
- Zubarev, Roman A., et al.
(author)
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Kinetic energies of secondary ions in MeV and keV particle-induced desorption
- 1996
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In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 10:15, s. 1966-1974
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Journal article (peer-reviewed)abstract
- Kinetic energy distributions of secondary ions produced by MeV or keV primary-ion bombardment of molecularsolids were measured in a reflectron time-of-flight mass spectrometer. It was found that the energy distributionsof many ions exhibit tails extending towards energies lower than the accelerating potential. The degree of tailingdepends upon the nature of the desorbed ion and the conditions of the target surface. Some light ions (H' andC' ), ions from inorganic (alkali halide) samples, radical molecular ions (Cg) and pre-formed molecuiar ions (e.g.complexes of valinomycin with alkali metal ions) exhibit almost no tailing. For positive adduct-type molecularions, such as MH', more extensive tailing was observed for MeV compared with keV primary ions. The originof the energy tailing is attributed to gas-phase formation of a fraction of the secondary ions. For molecular ionsof peptides, the characteristic time of formation of that fraction of ions (*lo% of the whole molecular-ionpopulation) was estimated to be of the order of 10 ns, while the characteristic distance from the target surfacewas of the order of 10 pm.
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8. |
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9. |
- Michelsen, P, et al.
(author)
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Quantification of polyphosphoinositides using selected ion monitoring electrospray mass spectrometry
- 1995
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In: Rapid Communications in Mass Spectrometry. - : Wiley. - 1097-0231 .- 0951-4198. ; 9:12, s. 1109-1114
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Journal article (peer-reviewed)abstract
- Polyphosphoinositides (PIP) and (PIP2) show prominent negative singly and doubly charged deprotonated molecules in electrospray mass spectrometry. These ions can be used for quantification of PIP and PIP2 in the low picomole range, without prior chromatographic separation, using selected ion monitoring and consecutive measurements of the signals from the deprotonated singly charged molecules. The dose response curves for both compounds are linear. In a complex matrix consisting of polar lipids (Folch extract) PIP and PIP2 monitored at m/z 965.4 and 1045.5 (stearoyl and arachidonoyl) were determined in the low picomole range, at a flow rate of 100 mu L/min, Collision-induced decomposition of PIP and PIP2 using a mixture of xenon and argon at 25 eV afforded identical high mass ions formed by loss of a molecule of water from PIP and a phosphate group and a molecule of water from PIP2. The results indicate that polyphosphoinositides, and biologically relevant changes in their concentrations, can be quantified directly in cells and cellular membranes by selected-ion monitoring with electrospray mass spectrometry.
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