Matrix-assisted Laser Desorption/Ionization by Two Collinear Subthreshold Laser Pulses

Tang, Xiaodong; Sadeghi, Mehrnoosh; Olumee, Zohra; Vertes, Akos

doi:10.1002/(sici)1097-0231(199703)11:5<484::aid-rcm895>3.0.co;2-2

Cited by 26 publications

(25 citation statements)

References 13 publications

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“…The results demonstrating the existence of a maximum at a specific delay time show evident similarities with experiments in the laser desorption of organic matrices using pump‐probe experiments 16–18. There are some differences in the timescale where the maximum ion yield takes place and these could be explained by the differences in the desorption mechanism and ionization threshold for organic matrices.…”

Section: Resultssupporting

confidence: 68%

“…The ionization threshold was calculated by exposing the sample to series of 50 laser pulses of increasing energy from 0.07 to 2 mJ/pulse (corresponding to fluence and irradiance intervals of 0.4–1.60 J cm −2 and 80–320 MW/cm 2 , respectively) while acquiring the individual mass spectra. The criterion followed has been previously used in similar experiments15 adapted from previous work in laser desorption 17. The experiments were performed over three consecutive days to rule out variations due to day‐to‐day fluctuations in the laser alignment or in the spatial profiles of the pump/probe beams.…”

Section: Resultsmentioning

confidence: 99%

“…In the present work, the dynamics of the ionization process on metals are followed by means of a pump‐probe experiment using two collinear beams set at sub‐threshold ionization fluences. These experiments have been previously used in the determination of desorption/ionization mechanisms in organic molecules 16–18. The aim of our research is to uncover the processes initiated by a sequence of two laser pulses, and to explore and understand the sub‐threshold processes involved in laser ionization of metallic targets.…”

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confidence: 99%

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Two‐pulse delayed 532‐nm laser ionization of metals using collinear sub‐threshold beams

Alcántara

Vadillo

Laserna

2008

Rapid Comm Mass Spectrometry

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Two frequency-doubled Nd:YAG lasers collinearly aligned were used to ionize different metals at specific interpulse delays. The beams were independently operated in order to attain full control over the energy. Each laser beam was always set at fluences below the ionization threshold and an evaluation of the effect that the interpulse delay has on the material ionization and the LIMS signal was performed. The different metallic targets studied (Cu, Si, Al, Ti, Fe, 314 AISI stainless steel) exhibit a characteristic ionization feature consisting of a clear enhancement in the ionization yield at interpulse delays around 60 ns when analyzed as pure foils. In addition, an improvement in the spectral resolution is observed at the specific interpulse delay. Our results indicate that proper control of the energy allows optimization of the different steps in the ionization process and they suggest that the effect of the first laser pulse impinging on the surface enhances the way in which the second pulse interacts with the solid.

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Section: Resultssupporting

confidence: 68%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Two‐pulse delayed 532‐nm laser ionization of metals using collinear sub‐threshold beams

Alcántara

Vadillo

Laserna

2008

Rapid Comm Mass Spectrometry

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“…If a laser‐plume ionization process were important, there might be an optimum pulse duration for maximum analyte ion yield, as observed in recent two‐pulse experiments 45. However, this pulse duration should in principle be correlated with the excited‐state lifetime of the matrix, a quantity that varies considerably among effective UV matrices 35, 45, 46. For example, DHB has only short‐lived excited states (τ ≈ 5 ns) while 3‐HPA fluoresces for tens of microseconds 46.…”

Section: Discussionmentioning

confidence: 99%

What do matrix‐assisted laser desorption/ionization mass spectra reveal about ionization mechanisms?

et al. 2002

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We present ion mass spectra obtained by matrix-assisted laser desorption/ionization for analytes of approximately 1000 Da across the largest range of wavelengths and pulse durations to date. The matrix used in all cases was 2,5-dihydroxybenzoic acid. Based on the data and fundamentals of laser-material interactions, we evaluated the plausibility of discriminating among such ion formation mechanisms as multiphoton ionization and excited-state ionization from mass spectra alone. Some previously proposed mechanisms appear unlikely for the matrix-analyte systems that we studied, casting doubt on their general applicability. Moreover, although analysis of mass spectra can apparently exclude certain mechanisms, it cannot establish which of several competing mechanisms is actually operative. This is particularly true with respect to variations in pulse duration and wavelength.

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“…Hence all these data show that desorption (or ablation) could start before ionization or on a comparable time‐scale. Experiments using two laser pulses21, 22 did not establish if ionization occurs when matrix molecules are in the solid state or in the ‘condensed gas’ state. Nevertheless, material ablation is a dynamic process in which molecules are initially at high density (i.e.…”

Section: Discussionmentioning

confidence: 99%

Delayed extraction experiments using a repulsing potential before ion extraction: evidence of non‐covalent clusters as ion precursor in UV matrix‐assisted laser desorption/ionization. Part II—Dynamic effects with α‐cyano‐4‐hydroxycinnamic acid matrix

et al. 2004

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Delayed extraction experiments were undertaken to gain a better insight into the dynamic effects involved in the ion formation in UV matrix-assisted laser desorption/ionization. Part I1 was devoted to a 2,5-dihydroxybenzoic (2,5-DHB) matrix. The results clearly demonstrated the existence and the role of high-mass precursors corresponding to a non-covalent matrix-analyte association in ion formation. In this complementary study, ion flight time and abundance were studied as a function of the delay extraction time using the matrix alpha-cyano-4-hydroxycinnamic acid (HCCA). Under our instrumental conditions, where ejected ions experienced a low repulsing electric field before extraction, two main results were obtained: (i) two ion components are observed in the peak profiles depending on the repulsing field, a first, major component (I) similar to that observed for 2,5-DHB and a second, minor component (II) apparently triggered by the delayed extraction pulse, and (ii) ion time-of-flight variation vs delay time remained lower than that noted with 2,5-DHB matrix, indicating that the initial axial velocity is smaller. The initial kinetic energy of matrix and low molecular mass peptide ions for the component I is not high enough to overcome the repulsing potential in the delay time range (200-2200 ns) and we have to assume that ions have non-covalent clusters as precursors. Complete desolvation of these clusters-aggregates would be achieved through the extraction step. Simulations of the ion time-of-flight as a function of the delay time allow the determination of the average size of the precursors, typically 4500, 40000 and 50000 u for HCCA, ACTH 7-38 and bovine insulin quasi-molecular ion, respectively, assuming that the precursors are singly charged. The size of these ion precursors is greater than that of those generated for 2,5-DHB. For component II, ions are probably not solvated and they are directly desorbed from the target. Taking into account the results on HCCA and 2,5-DHB matrices and other results from the literature, a general model for ion formation based on clusters as ion precursors is proposed and discussed.

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Matrix-assisted Laser Desorption/Ionization by Two Collinear Subthreshold Laser Pulses

Cited by 26 publications

References 13 publications

Two‐pulse delayed 532‐nm laser ionization of metals using collinear sub‐threshold beams

Two‐pulse delayed 532‐nm laser ionization of metals using collinear sub‐threshold beams

What do matrix‐assisted laser desorption/ionization mass spectra reveal about ionization mechanisms?

Delayed extraction experiments using a repulsing potential before ion extraction: evidence of non‐covalent clusters as ion precursor in UV matrix‐assisted laser desorption/ionization. Part II—Dynamic effects with α‐cyano‐4‐hydroxycinnamic acid matrix

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