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A kinematic model for the laser-induced introduction into the gas phase of large molecules embedded in a host matrix is discussed. The desorption of undegraded large molecules is argued to be a kinetic effect due to potentially rapid destruction of the host matrix. The two separate mechanisms are considered, sublimation and fragmentation of the matrix. Due to the choice of hosts, sublimation is more typical of experiments using UV laser pulses. In general, sublimation is found to be more efficient because it can turn itself off. The matrix destruction competes with host—guest vibrational energy transfer. The energy content of the guest can be reduced by working at low volume concentrations, special choice of host matrices and using an initially cold sample.

Ambient ionization methods in mass spectrometry allow analytical investigations to be performed directly on a tissue or biofilm under native-like experimental conditions. Laser ablation electrospray ionization (LAESI) is one such development and is particularly well-suited for the investigation of water-containing specimens. LAESI utilizes a mid-infrared laser beam (2.94 μm wavelength) to excite the water molecules of the sample. When the ablation fluence threshold is exceeded, the sample material is expelled in the form of particulate matter and these projectiles travel to tens of millimeters above the sample surface. In LAESI, this ablation plume is intercepted by highly charged droplets to capture a fraction of the ejected sample material and convert its chemical constituents into gas-phase ions. A mass spectrometer equipped with an atmospheric-pressure ion source interface is employed to analyze and record the composition of the released ions originating from the probed area (pixel) of the sample. A systematic interrogation over an array of pixels opens a way for molecular imaging in the microprobe analysis mode. A unique aspect of LAESI mass spectrometric imaging is depth profiling that, in combination with lateral imaging, enables three-dimensional (3D) molecular imaging. With current lateral and depth resolutions of ~100 μm and ~40 μm, respectively, LAESI mass spectrometric imaging helps to explore the molecular structure of biological tissues. Herein, we review the major elements of a LAESI system and provide guidelines for a successful imaging experiment.

Neutralization reaction was investigated in negative ferric hydrous oxide sols. The adsorption isotherm of OH - ions on the surface of colloidal particles was measured to provide the variation of their charge with pH. Impulse radiolysis generated the reacting ions in the sol. Using a fast DC conductivity setup for detection, a significant increase in the neutralization rate coefficient was found at low OH - concentrations. The phenomenon was discussed in terms of the theory of diffusion controlled reactions for particles interacting with Coulomb and Yukawa potential.

Parametric studies were conducted to design, develop, and integrate three gas chromatographic columns with a miniaturized mass spectrometer to be part of the Cassini−Huygens mission for studying the atmosphere of Saturn's moon Titan. Separation and identification of low-molecular-weight hydrocarbons and nitriles (important prebiological molecules) were carried out on dimethylpolysiloxane (DMPS) and 14% cyanopropylphenyl−86% dimethylpolysiloxane (CPPS−DMPS) column stationary phases. These phases were deposited as thin films on the inner surface of fused silica coated steel capillary columns. The interaction of hydrocarbons and nitriles with these phases was studied under various column inlet pressure and carrier gas flow conditions. The selectivity for nitriles was enhanced by using the CPPS−DMPS phase. On this phase, the modeling number (log M) values varied linearly with the column temperature. Pronounced differences were observed in the order of elution for C4 hydrocarbons between CPPS−DMPS and DMPS pha...

Applicability of the fluctuation model was tested in the case of n‐hexane, n‐pentane, c‐hexane, 2,2‐dimethylbutane, 2,2,4,4‐tetramethylpentane, iso‐octane, and neopentane. In our model, the quasifree electrons have been assumed to be scattered by the conduction state energy fluctuations of the liquid. These fluctuations are, in turn, described as a consequence of density fluctuations. The scattering potential is supposed to be square well like and the cross section is calculated in terms of partial waves. Averages due to the density fluctuations and the electron kinetic energy distribution are determined numerically. Except for the first three materials, the calculation reproduced the experimental mobilities with reasonable values of the square well radius, which is the only fitting parameters. Further extension of the description concerning the density dependence of the low field mobility of fluid argon has been performed. The estimated fluctuation size as a function of density increases monotonically at...

Electrosprays have diverse applications including protein analysis, electrospinning, and nanoencapsulation for drug delivery. We show that a variety of electrospray regimes exhibit fundamental analogy with the nonlinear dynamics of a dripping faucet. The applied voltage in electrosprays results in additional period doublings and temporal order-chaos-order transitions. Attractors in the return maps show logarithmic self-similarity in time, suggesting self-similar capillary waves on the meniscus. The bifurcations in ejection time can be explained by phase variations between capillary waves and pinch-off conditions and by ejection mode changes due to contact angle variations.

Expansion of laser-produced plumes on a solid-vacuum in’ terface during and after the laser shot was investigated theoretically, incorporating several new features into our previous one-component one-dimensional hydrodynamic model. Time development of density, velocity, temperature, and pressure profiles was calculated at laser irradiances below and above the plasma ignition threshold. The estimated velocity of ions released from the plume was close to the measured values. The fast spreading of the blow-off material under the laser vaporization regime and the long lifetime of the relatively compact plasma core above the ignition threshold were predicted in agreement with experimental observations. Cakulated surface recession due to evaporation provided a Jower bound to the measured crater depth, whereas the calculated melt depth proved to be a realistic upper limit.

Molecular dynamics simulations of matrix-assisted laser desorption ionization (MALDI) were conducted using a detailed description of the internal degrees of freedom for both matrix (nicotinic acid) and guest (leucine enkephalin) molecules. Afforded by the separate treatment of matrix and guest properties, the energy transfer and the conformation dynamics were followed throughout the desorption process. The effect of the initial matrix temperature and the influence of guest molecule burial depth and charge state were investigated. Elevating the initial temperature of the matrix increased the desorption velocity of the guest molecules, but only a small change in their postdesorption internal temperature was seen. This observation may account for the lack of thermodecomposition of large guest molecules in MALDI. The liftoff velocity of the guest molecules dropped significantly as the burial depth was increased from 5 to 20 A, indicating that the guest molecules located near the surface entered the plume with...

Plasma ion sources are constantly growing in importance in the field of atomic mass spectrometry. The idea is to deposit enough energy into the analyte to atomize and ionize a representative part of it and to achieve a plasma state that will endure for some period of time. A fraction of the ions can then be extracted from the plasma and analyzed in the mass spectrometer. The main difference among the methods for plasma ionization lies in the form in which energy is delivered to the sample. Either it is in the form of electric current (glow discharge, spark) or it is mediated by electromagnetic radiation (inductively coupled plasma (ICI’), microwave-induced plasma (MU’), pulsed laser). The present state of the art in using these sources in analytical applications is well summarized in a recent review (1) and in a recently published monograph (2). Plasma ion sources are not only used in mass spectrometers, but have become essential parts of ion implanters, accelerators, nuclear fusion devices, etc. (3). For ion implantation, ion milling, and etching purposes, hollow cathode (4), plasma cathode (5-8), radiofrequency (9) and microwave ion sources (10-12) are under intense investigation. Diligent research is devoted to the ever-improving ion sources for accelerator and nuclear fusion applications. Multicusp (13-16), surface plasma (17), hollow cathode (18), microwave (19), alkaline anode (20-22), radial field discharge (23), and micropinch (24) sources are among the subjects of current interest. We refer to the multitude of these plasma ion source construction efforts only because-as has happened already many times before-new mass spectrometric sources may emerge from such developments. Of these methods hollow cathode sources are familiar to the analytical spectroscopist, and microwave sources are just about to debut in mass spectrometry. The expected properties of the source depend on the particular demands of *To whom correspondence should be addressed. Phone: [323] 820.23.82. Electronic mail: VERTES@BANUIA52.BITNET. On leave from: Central Research Institute for Physics of the Hungarian Academy of Sciences.

Electrospray ion sources efficiently produce gas-phase ions from proteins and their noncovalent complexes. Charge-state distributions of these ions are increasingly used to gauge their conformations in the solution phase. Here we investigate how this correlation is affected by the spraying conditions at the early stage of droplet generation, prior to the ionization process. We followed the folding behavior of model proteins cytochrome c and ubiquitin and the dissociation of the noncovalent holomyoglobin complex. Spray current measurements, fast Taylor cone imaging, and mass analysis of the generated ions indicated that the protein structure experienced conformational or complexation changes upon variations in the spraying mode of the electrospray ionization source. These effects resulted in a departure from the original secondary, tertiary, and quaternary structure of proteins, possibly introducing artifacts in related studies. Therefore, if a particular gas-phase ion conformation is required or correlations with the liquid-phase conformations are studied, it is advantageous to maintain a particular spraying mode. Alternatively, spraying mode-induced changes can be utilized to alter the structure of proteins in, for example, time-resolved experiments for the study of protein folding dynamics.

Analysis of biochemicals in single cells is important for understanding cell metabolism, cell cycle, adaptation, disease states, etc. Even the same cell types exhibit heterogeneous biochemical makeup depending on their physiological conditions and interactions with the environment. Conventional methods of mass spectrometry (MS) used for the analysis of biomolecules in single cells rely on extensive sample preparation. Removing the cells from their natural environment and extensive sample processing could lead to changes in the cellular composition. Ambient ionization methods enable the analysis of samples in their native environment and without extensive sample preparation.1 The techniques based on the mid infrared (mid-IR) laser ablation of biological materials at 2.94 μm wavelength utilize the sudden excitation of water that results in phase explosion.2 Ambient ionization techniques based on mid-IR laser radiation, such as laser ablation electrospray ionization (LAESI) and atmospheric pressure infrared matrix-assisted laser desorption ionization (AP IR-MALDI), have successfully demonstrated the ability to directly analyze water-rich tissues and biofluids at atmospheric pressure.3-11 In LAESI the mid-IR laser ablation plume that mostly consists of neutral particulate matter from the sample coalesces with highly charged electrospray droplets to produce ions. Recently, mid-IR ablation of single cells was performed by delivering the mid-IR radiation through an etched fiber. The plume generated from this ablation was postionized by an electrospray enabling the analysis of diverse metabolites in single cells by LAESI-MS.12 This article describes the detailed protocol for single cell analysis using LAESI-MS. The presented video demonstrates the analysis of a single epidermal cell from the skin of an Allium cepa bulb. The schematic of the system is shown in Figure 1. A representative example of single cell ablation and a LAESI mass spectrum from the cell are provided in Figure 2.

Potential distribution and ion trajectory calculations involving time development of the ion motion in laser microprobe mass spectrometers have been performed. Potential distribution calculations were based on the Fourier transformation technique since this offers improved effectiveness. The time-dependent ion trajectories that were calculated showed different flight times for ions with different initial conditions. Transmission properties of the angle focusing “einzel” lens are discussed with special emphasis on lens potential and ion formation position dependence. Qualitative agreement with experimental findings is demonstrated. It was shown that, if the geometrical parameters of the instrument are optimized, an arrangement promising similar performance to that of LAMMA 500 can be obtained but with more compact design. Peak shape calculations were carried out for different initial kinetic energy and departing angle distributions. Peak broadening, shift, and asymmetry could be explained in terms of the width of ion energy distribution. However, no dramatic broadening was observed according to the second-order energy focusing property of the ion reflector.

During the desorption and ionization processes in matrix-assisted laser desorption ionization MALDI , the laser beam interacts with different areas of the polycrystalline sample surface varying in crystal size and structure. CCD imaging of dried-droplet and electrospray deposited MALDI samples was used to explore the effect of laser exposure on surface morphology at atmospheric pressure. Crystal size distributions of the sinapinic acid target were examined prior to and after laser irradiation. Image processing and analysis of the difference images revealed the morphological changes in the sample. . The results indicate that near-threshold irradiance smaller crystals ; 2 mm are completely volatilized by the laser shot, . whereas larger crystals undergo layer-by-layer evaporation peeling . Heat conduction simulations in a finite slab have demonstrated that under similar conditions, the surface temperature of small crystallites increases markedly compared to their larger counterparts. These higher surface temperatures can lead to the selective volatilization of smaller crystallites. This study points to the influence of sample preparation on the crystal size distribution and its consequence on volatilization . in MALDI-mass spectrometry MS . q 1998 Elsevier Science B.V. .

A one-component one-dimensional (1C–1D) hydrodynamic model has been developed to describe the expansion of laser-generated plumes in ion sources. The model incorporates the conservation formalism of hydrodynamics, normal and plasma absorption mechanisms of laser-target coupling and the local thermal equilibrium condition for ionization. The considerable difficulties (non-linearities, shock waves) in finding the solution were overcome by using the Godunov algorithm. A comprehensive study of the model covered three different laser types (ruby, CO2 and frequency-quadrupled Nd-YAG) and three classes of solid targets (metals, transparent insulators and opaque insulators). Density, velocity and temperature profiles across the expanding plume were evaluated at the end of the laser pulse, to yield crater depths, cloud extensions, ion yields, relative sensitivity factors and ion kinetic energy distributions, i.e. quantities more closely related to experimental data. Although calculated crater depths significantly exceeded the measured values, they show strong correlation with them. We found that the extension of the gas cloud varied with the laser power density according to a power law. A similar conclusion can be drawn from expansion velocity measurements (even providing exponents that are close in value). Calculated ion yield versus laser intensity curves show the typical threshold behaviour separating laser desorption and laser plasma ionization. In the plasma ionization mode the known uniform relative sensitivity factors were recovered. Ion kinetic energy distributions were investigated under typical laser desorption and laser plasma ionization conditions. The energy spectrum of the desorbed ions extended up to 1 eV, in good agreement with measured spectra. Laser plasma ionization provided ions with up to 100 eV, therefore somewhat underestimating experimental values.

Two nitrogen laser pulses of subthreshold irradiance were used to achieve matrix-assisted laser desorption/ionization in a collinear configuration. Optimum laser pulse delay times yielding maximum guest ion intensities were determined for four different matrices between 4.2 ns for sinapinic acid (SA) and 12.5 ns for 2,5-dihydroxybenzoic acid (DHB). The signal decay times followed an opposite trend to the position of maxima, DHB being the fastest decaying (1.1 ns) and SA the slowest (9.8 ns). Collinear subthreshold experiments allow for a two orders of magnitude improvement in spatial and time resolution over post-ionization experiments. © 1997 by John Wiley & Sons, Ltd.

The time of flight (TOF) method has been utilized to measure kinetic energy distributions of ions generated by laser ionization sources. Measurements were carried out on carbon foil targets with pulses from a Q-switched ruby laser in the power density range from 106 to 1010 W cm−2. the onset of plasma formation and appearance of positive and negative energy ions were observed. Interference of neighbouring lines could be resolved by decreasing the light intensity down to the plasma formation threshold. The energy spectrum consisted of a positive energy peak and negative energy tail centered around the ideal symmetrical peak. The appearnace of these characteristics depended on the laser power density applied. The positive energy part of the energy spectrum was related to the shock wave due to laser heating of the foil while the negative energy part could be explained by post-ionization of neutrals in the accelerating region. Shock fitting according to Godunov served as a rough estimate for plasma hydrodynamics, while an optical and charge transfer model as a possible description of the negative part of the energy spectrum were discussed. Encouraging correlations between measured and calculatd data were found.

Most cultured cells used for biomedical research are cultured adherently, and the requisite detachment prior to biochemical analysis might induce chemical changes. This is especially crucial if accurate metabolic measurements are desired, given the rapid turnover of metabolites in living organisms. There are only a few methods available for the nontargeted in situ analysis of small adherent cell populations. Here we show that laser ablation electrospray ionization (LAESI) mass spectrometry (MS) can be used to analyze adherent cells directly, while still attached to the culture surface. To reduce the size of the analyzed cell population, the spot size constraints of conventional focusing in reflection geometry (rg) LAESI had to be eliminated. By introducing transmission geometry (tg) LAESI and incorporating an objective with a high numerical aperture, spot sizes of 10-20 μm were readily achieved. As few as five adherent cells could be specifically selected for analysis in their culturing environment. The importance of in situ analysis was highlighted by comparing the metabolite composition of adherent versus suspended cells. For example, we observed that cells analyzed adherently yielded higher values for the adenylate energy charge (0.90 ± 0.09 for adherent cells vs 0.09 ± 0.03 for suspended cells). Additionally, due to the smaller focal spot size, tg-LAESI enabled the analysis of ∼20 times smaller cell populations compared to rg-LAESI.

The etching rate of Mo samples in a planar glow discharge configuration using Ar as discharge gas is measured as a function of applied power density (0–10 W cm 2 ) and pressure inside the discharge cell (365–750 mTorr). These etching rates are compared with calculated values obtained by modeling of a one dimensional planar glow discharge. The structure of the cathode fall region is modeled in terms of a set of one-dimensional Boltzmann equations describing the three main particle types, ions, neutrals and electrons. Numerical solution of these equations provide the etching rate of the target and the energy distributions of the components. Satisfactory correlation between the measured and calculated etching rates allowed it to conclude also that other quantities for understanding plasma processes like the diffusion profiles of sputtered neutrals can reliably be predicted.

Astable regimes are common in nonlinear systems ranging from electrooptic devices to cardiac rhythms under environmental stress. Electrosprays exhibit three main axial regimes (dripping, pulsating, and cone-jet). It is generally accepted that the transition between the pulsating and cone-jet regimes is sudden, accompanied by an abruptly enhanced spray current. Here we present an alternative to this scenario, in which the electrospray follows a new chaotic astable path to the cone-jet regime. The astable regime could be explained as a result of transitions between a limit cycle (pulsating regime) and a fixed point (cone-jet regime) in a subcritical Andronov-Hopf bifurcation due to small external perturbations (noise). With the introduction of this regime, a broader view of the diverse axial regimes becomes possible based on nonlinear dynamics that enables their consistent classification.

The method of partial waves in the framework of the fluctuation model has been applied to describe the density dependence of the electron mobility in liquid xenon. The limiting factor in the transport of excess electrons in such systems can be attributed to their scattering due to density fluctuations. Instead of the usual Born approximation we handled the scattering problem with the more general method of partial waves. This made it possible to work out the average fluctuation size from the transport data. Calculations were carried out in the density range (6.7-11.5) x 10/sup 21/ atoms/cm/sup 3/. Good agreement with measured mobility curves can be obtained by considering reasonable values for the average fluctuation size.

Atmospheric pressure (AP) infrared (IR) matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) was demonstrated for the rapid direct analysis of pharmaceuticals, and excreted human metabolites. More than 50 metabolites and excreted xenobiotics were directly identified in urine samples with high throughput. As the water content of the sample was serving as the matrix, AP IR-MALDI showed no background interference in the low mass range. The structure of targeted ions was elucidated from their fragmentation pattern using collision activated dissociation. The detection limit for pseudoephedrine was found to be in the sub-femtomole range and the semi-quantitative nature of the technique was tentatively demonstrated for a metabolite, fructose, by using a homologous internal standard, sucrose. A potential application of AP IR-MALDI for intestinal permeability studies was also explored using polyethylene glycol.

Using molecular dynamics simulations we have demonstrated that the guest species in matrix-assisted laserdesorption exhibits significantly different conformations in the gas phase, on the crystal surface, and embeddedinto the matrix. Our model fully accounted for the internal structure of matrix and guest molecules; thus, wewere able to follow the details of conformational changes in the guest molecule within the crystal and throughoutthe desorption. During the embedding process, simulated by sinapinic acid crystal growth around the substanceP guest species, changes in the guest species conformation were investigated. While the guest species placedon the surface of the host crystal exhibited two hydrogen bonds on the backbone and one turn, the conformationof the embedded species contained three hydrogen bonds and two turns. Independent of the burial depth, theconformation of the guest species within the crystal remained the same. After laser heating and during thedesorption process, no preferred gas-phase conformation was observed. Investigation of the radius-of-gyrationof the guest species originating from different layers of the crystal revealed that, upon desorption, the guestspecies did not sustain a stable conformation in the gas phase. Liftoff velocities of the guest species embeddedin various layers of the host crystal and on the surface were similar to the liftoff velocities of the matrixmolecules around them. This is an indication of the entrainment of guest species by the matrix plume.Investigation of the energy histories of the matrix and guest species showed lower internal and kinetictemperatures for the latter, which could explain the absence of fragmentation in MALDI. Results also showedthat maximum energy transfer occurred during the phase transition of the host crystal at which time the guestspecies were released from the crystal. Examining the noncovalent complex of the guest species and sinapinicacid anions showed that the complex remained intact throughout the desorption process. A similar phenomenonis often reflected in MALDI mass spectra, in the form of guest-matrix adduct peaks.

BackgroundViral transformation of a cell starts at the genetic level, followed by changes in the proteome and the metabolome of the host. There is limited information on the broad metabolic changes in HTLV transformed cells.Methods and principal findingsHere, we report the detection of key changes in metabolites and lipids directly from human T-lymphotropic virus type 1 and type 3 (HTLV1 and HTLV3) transformed, as well as Tax1 and Tax3 expressing cell lines by laser ablation electrospray ionization (LAESI) mass spectrometry (MS). Comparing LAESI-MS spectra of non-HTLV1 transformed and HTLV1 transformed cells revealed that glycerophosphocholine (PC) lipid components were dominant in the non-HTLV1 transformed cells, and PC(O-32:1) and PC(O-34:1) plasmalogens were displaced by PC(30:0) and PC(32:0) species in the HTLV1 transformed cells. In HTLV1 transformed cells, choline, phosphocholine, spermine and glutathione, among others, were downregulated, whereas creatine, dopamine, arginine and AMP were present at higher levels. When comparing metabolite levels between HTLV3 and Tax3 transfected 293T cells, there were a number of common changes observed, including decreased choline, phosphocholine, spermine, homovanillic acid, and glycerophosphocholine and increased spermidine and N-acetyl aspartic acid. These results indicate that the lipid metabolism pathway as well as the creatine and polyamine biosynthesis pathways are commonly deregulated after expression of HTLV3 and Tax3, indicating that the noted changes are likely due to Tax3 expression. N-acetyl aspartic acid is a novel metabolite that is upregulated in all cell types and all conditions tested.Conclusions and significanceWe demonstrate the high throughput in situ metabolite profiling of HTLV transformed and Tax expressing cells, which facilitates the identification of virus-induced perturbations in the biochemical processes of the host cells. We found virus type-specific (HTLV1 vs. HTLV3), expression-specific (Tax1 vs. Tax3) and cell-type-specific (T lymphocytes vs. kidney epithelial cells) changes in the metabolite profiles. The new insight on the affected metabolic pathways can be used to better understand the molecular mechanisms of HTLV induced transformation, which in turn can result in new treatment strategies.

International audience; KSHV is the causative agent of three human proliferative disorders: Kaposi s sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. Herpesvirus gene expression and viral replication is a complex, tightly regulated process involving latent, immediate early, early, and late viral gene transcription. The immediate early genes generally code for transcriptional activators and are critical for initiating viral transcription. KSHV encodes for approximately nine immediate early gene products, including ORF50, K8, K9, K3, K5, ORF57, ORF29b, ORF45, and K4.2. This review will address the activities of these proteins and what roles they play in virus replication, evasion of the host immune response, and viral pathogenesis.