On initial ion velocities in MALDI: A novel FT-ICR MS approach

doi:10.1016/j.ijms.2014.08.004

International Journal of Mass Spectrometry

Volume 372, 1 November 2014, Pages 51-53

https://doi.org/10.1016/j.ijms.2014.08.004 Get rights and content

Highlights

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New way for measuring ion velocity distributions in MALDI and LDI.
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An internal MALDI source FT-ICR mass spectrometer is used.
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Arrival times of the ions in the ICR cell are determined.
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No influence of electric fields in the direction of the instrument axis.
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The angular velocity distribution can be estimated as well.

Abstract

Even after more than two decades of investigation, the question whether the initial velocity of ions generated by matrix-assisted laser desorption/ionization (MALDI) depends on their molecular weight or not remains unanswered. A novel method employing an internal MALDI source Fourier-transform ion cyclotron resonance mass spectrometry is used to measure the initial ion velocities of peptides with m/z values in the range of typical proteomic experiments. Simultaneous measurement of multiple matrix and analyte ions clearly shows initial ion velocities that depend on analyte or matrix molecular weight. The measured velocity values agree well with the published data.

Graphical abstract

An internal MALDI source FT-ICR MS was used to measure initial ion velocities. The initial velocity of ions was observed to depend on the molecular weight of analytes.

Section snippets

Acknowledgements

We appreciate the support from ETH Zürich, grant No ETH-22 11-2 and the Program of Employment of Newly Graduated Doctors of Science for Scientific Excellence (CZ.1.07/2.3.00/30.0009) co-financed by the European Social Fund and the Czech Republic.

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There are more references available in the full text version of this article.

Cited by (10)

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This work examines how ion acceleration parameters affect the mass resolving power (R_m) of linear time-of-flight (TOF) mass spectrometry (MS). Ion acceleration parameters have been considered as playing a minor role in determining the R_m in TOF MS. Based on results in two-dimensional topological space calculated in this work, we demonstrate that the length and electrical potential of the ion acceleration region critically affect R_m. The flight-time distribution of ions of m/z 3000 in a 3-m long linear TOF mass spectrometer is analyzed using the coupled space-velocity focusing method. Big data analysis reveals that four types of flight-time distribution are available by adjusting ion acceleration length. The coefficients in the equation of flight-time spread can be used to predict the best length for achieving highest performance. The results show an 18-fold increase in R_m when increasing the length of the ion acceleration region by a factor of ∼35 with respect to conventional design. Adjusting ion extraction parameters cannot provide the same magnitude of improvement. Correlation between R_m and critical experimental parameters are discussed.
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Citation Excerpt :
Experimental observations of Hertel et al. [47], Kappes et al. [45], Kirsch et al. [11], and Ni et al. [48] also support the observation that the mean initial velocity of ions increases with laser pulse energy. However, Zenobi et al. reported a different finding; they reported that the initial ion velocity of bradykinin 2–9 fragment ions was independent of laser pulse energy [13]. They measured the ion velocities without any influence of electric fields in the direction of the instrument axis before ions reached the ICR cell.
This paper is a study of the effects of quadrupole electric fields on the velocities of ions generated by laser desorption ionization (LDI). We used a charge detector to measure ion flight time in the absence of electric and magnetic fields to obtain the initial velocity distribution of ions generated in the LDI process. It was found that the measured ion velocity of fullerene and matrix ions was proportional to the energy of the laser pulse. Then we measured velocity distributions of fullerene ions in rf-only quadrupoles. It was observed that the electric field in the fringing field region was proportional to pseudo-potential well depth (D_z) and that ions gained velocity in the fringing field region and speeded up as the D_z was increased due to transfer of rotational energy into translational energy in the high-order field region. Initial velocity of ions passing through different stages of quadruple was increased at every stage. In addition, the mass spectrometric analysis showed when the rf amplitude was low, the quadrupole field allowed stable motion of low mass ions; when the rf amplitude was increased, effective potential well depth was reduced. This is evident that the gradient of ion velocity drops as the difference in D_z increases for C₆₀ and high mass C_n cluster ions.
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Short communicationOn initial ion velocities in MALDI: A novel FT-ICR MS approach

Highlights

Abstract

Graphical abstract

Section snippets

Acknowledgements

J. Am. Soc. Mass Spectrom.

Chem. Phys. Lett.

Int. J. Mass Spectrom.

The initial ion velocity and its dependence on matrix, analyte and preparation method in ultraviolet matrix-assisted laser desorption/ionization

J. Mass Spectrom.

Short communication
On initial ion velocities in MALDI: A novel FT-ICR MS approach