From electrospray ionization to cold-spray ionization: How to evaluate the cooling effect on the gaseous ions?

Two methods of survival yields (SY) measurement treatment of thermometer ions whose fragmentation is activated by in-source collision induced dissociation have been investigated for evaluating the mean internal () and thermal () energies of gaseous ions produced by electrospray ionization and cold-spray ionization (CSI). One of the methods is based on the use of the internal energy distributions (P (Eint )) as sigmoid derivatives connecting the experimental survival yields of different substituted benzylpyridinium cations. The values are therefore converted in a thermal-like parameter called vibrational temperature (Tvib ) then obtained at each value of the voltage of the desolvation area. The second method is based on the modelling of ion behavior by the MassKinetics software where the value of the characteristic temperature parameter (Tchar ) is used for fitting theoretical survival yields (SYtheo ) with experimental data (SYexp ) calculated at several activation energy. A linear correlation is evidenced between the values of internal or thermal energy and the voltage of the orifice 1 at the origin of the ion activation in the desolvation area. The extrapolation at zero voltage of the thermal-like parameters (Tvib and Tchar ) indicates that, in agreement with the literature data, the ions are relatively hot in ESI (~650 K). But the use of a CSI source lowers this temperature down to ~300 K. In addition, with cold-spray ionization, this cooling effect is more important when methanol is used instead of acetonitrile although these two solvents have no influence on the gaseous ion temperature in electrospray ionization.

Evaluation for Ion Heating of H2A-H2B Dimer in Ion Mobility Spectrometry-Mass Spectrometry

Ion mobility spectrometry-mass spectrometry (IMS-MS) provides m/z values and collision cross sections (CCSs) of gas-phase ions. In our previous study, an intrinsically disordered protein, the H2A-H2B dimer, was analyzed using IMS-MS, resulting in two conformational populations of CCS. Based on experimental and theoretical approaches, this resulted from a structural diversity of intrinsically disordered regions. We predicted that this phenomenon is related to ion heating in the IMS-MS instrument. In this study, to reveal the effect of ion heating from parameters in the IMS-MS instrument on the conformational population of the H2A-H2B dimer, we investigated the arrival time distributions of the H2A-H2B dimer by changing values of three instrumental parameters, namely, cone voltage located in the first vacuum chamber, trap collision energy (trap CE) for tandem mass spectrometry, and trap bias voltage for the entrance of IMS. These results revealed that the two populations observed for the H2A-H2B dimer were due to the trap bias voltage. Furthermore, to evaluate the internal energies of the analyte ions with respect to each parameter, benzylpyridinium derivatives were used as temperature-sensitive probes. The results showed that the trap CE voltage imparts greater internal energy to the ions than the trap bias voltage. In addition, this slight change in the internal energy caused by the trap bias voltage resulted in the structural diversity of the H2A-H2B dimer. Therefore, the trap bias voltage should be set with attention to the properties of the analytes, even if the effect of the trap bias voltage on the internal energy is negligible.

Solvent Adducts in Ion Mobility Spectrometry: Toward an Alternative Reaction Probe for Thermometer Ions

The fragmentation of benzylpyridinium "thermometer" ions is widely used to quantify the energetics of ions studied by mass spectrometry and other hyphenated techniques such as ion mobility. The reaction pathway leads to a benzylium cation with the release of a neutral pyridine. Using trapped ion mobility spectrometry, we noticed that the addition of acetonitrile, present in the electrosprayed solvent mixture, could occur on some electrophilic benzylium cations. This process results in the formation of adducts and in the appearance of a supplementary mobility peak. We here demonstrate that the addition takes place both in the electrospray source and inside the mobility analyzer, thereby evidencing possible outflow of solvent vapors downstream the instrument. By further characterizing the initial kinetics and the resulting equilibrium linked with the addition reaction, we presently discuss these as alternative probes to calibrate ion temperature in the framework of ion mobility.

Storage of Energy in Constrained Non-Equilibrium Systems

We study a quantity T defined as the energy U, stored in non-equilibrium steady states (NESS) over its value in equilibrium U0, ΔU=U−U0 divided by the heat flow JU going out of the system. A recent study suggests that T is minimized in steady states (Phys.Rev.E.99, 042118 (2019)). We evaluate this hypothesis using an ideal gas system with three methods of energy delivery: from a uniformly distributed energy source, from an external heat flow through the surface, and from an external matter flow. By introducing internal constraints into the system, we determine T with and without constraints and find that T is the smallest for unconstrained NESS. We find that the form of the internal energy in the studied NESS follows U=U0∗f(JU). In this context, we discuss natural variables for NESS, define the embedded energy (an analog of Helmholtz free energy for NESS), and provide its interpretation.

Extreme Foaming Modes for SCF-Plasticized Polylactides: Quasi-Adiabatic and Quasi-Isothermal Foam Expansion

The experimental evidence on depressurization foaming of the amorphous D,L-polylactide, which is plasticized by subcritical (initial pressures below the critical value) or supercritical (initial pressures above the critical value) carbon dioxide at a temperature above the critical value, relates to two extreme cases: a slow quasi-isothermal foam expansion, and a rapid quasi-adiabatic expansion. Under certain conditions, the quasi-isothermal mode is characterized by the non-monotonic dependencies of the foam volume on the external pressure that are associated with the expansion-to-shrinkage transition. The quasi-adiabatic and quasi-isothermal expansions are characterized by a significant increase in the degree of foam expansion under conditions where the CO₂ initial pressure approaches the critical value. The observed features are interpreted in terms of the energy balance in the foam volume and the phenomenological model based on the equation of the foam state. The expansion-to-shrinkage condition is based on the relationship between the average bubble radius and the pressure derivative of the surface tension for the plasticized polylactide. The maximum expansion ratio of the rapidly foamed polylactide in the vicinity of the critical point is interpreted in terms of the maximum decrement of the specific internal energy of the foaming agent (carbon dioxide) in the course of depressurization.

Extended kinetic method and RRKM modeling to reinvestigate proline's proton affinity and approach the meaning of effective temperature

Proline proton affinity PA(Pro) was previously measured by extended kinetic methods with several amines as reference bases using a triple quadrupole mass spectrometer ( J Mass Spectrom 2005; 40: 1300). The measured value of 947.5 ± 5 kJ.mol^-1 differs by more than 10 kJ.mol^-1 from previous reported experimental or calculated values. This difference may be explained in part by the existence of relatively large entropy difference between the two dissociation channels (ΔΔS^‡_avg = 31 ± 10 J.mol^-1.K^-1) and by the inaccuracy of the amines proton affinity used as reference bases. In the present work, these experimental measurements were reinvestigated by RRKM modeling using MassKinetics software. From this modeling, a new PA value of 944.5 ± 5 kJ.mol^-1 and a ΔΔS^‡_avg(600K) value of 33 ± 10 J.mol^-1.K^-1 are determined. However, the difference between experiment and recent theoretical calculations remains large (10 kJ.mol^-1). These RRKM simulations allow also accessing to the effective temperature parameter (T _eff) and to discuss the meaning of this term. As previously reported, T _eff mainly depends on the internal energy and on the decomposition time as well. It also depends on the critical energies and on the transition state. Considering the entrance of the collision cell as a new ion source, T _eff is finally shown to be close to a characteristic temperature (T _char).

Thermodynamic Analysis of Time Evolving Networks

The problem of how to represent networks, and from this representation, derive succinct characterizations of network structure and in particular how this structure evolves with time, is of central importance in complex network analysis. This paper tackles the problem by proposing a thermodynamic framework to represent the structure of time-varying complex networks. More importantly, such a framework provides a powerful tool for better understanding the network time evolution. Specifically, the method uses a recently-developed approximation of the network von Neumann entropy and interprets it as the thermodynamic entropy for networks. With an appropriately-defined internal energy in hand, the temperature between networks at consecutive time points can be readily derived, which is computed as the ratio of change of entropy and change in energy. It is critical to emphasize that one of the main advantages of the proposed method is that all these thermodynamic variables can be computed in terms of simple network statistics, such as network size and degree statistics. To demonstrate the usefulness of the thermodynamic framework, the paper uses real-world network data, which are extracted from time-evolving complex systems in the financial and biological domains. The experimental results successfully illustrate that critical events, including abrupt changes and distinct periods in the evolution of complex networks, can be effectively characterized.

Investigation of Finite-Size 2D Ising Model with a Noisy Matrix of Spin-Spin Interactions

We analyze changes in the thermodynamic properties of a spin system when it passes from the classical two-dimensional Ising model to the spin glass model, where spin-spin interactions are random in their values and signs. Formally, the transition reduces to a gradual change in the amplitude of the multiplicative noise (distributed uniformly with a mean equal to one) superimposed over the initial Ising matrix of interacting spins. Considering the noise, we obtain analytical expressions that are valid for lattices of finite sizes. We compare our results with the results of computer simulations performed for square N = L × L lattices with linear dimensions L = 50 ÷ 1000. We find experimentally the dependencies of the critical values (the critical temperature, the internal energy, entropy and the specific heat) as well as the dependencies of the energy of the ground state and its magnetization on the amplitude of the noise. We show that when the variance of the noise reaches one, there is a jump of the ground state from the fully correlated state to an uncorrelated state and its magnetization jumps from 1 to 0. In the same time, a phase transition that is present at a lower level of the noise disappears.

Dissociation Pathways of Benzylpyridinium "Thermometer" Ions Depend on the Activation Regime: An IRMPD Spectroscopy Study

The dissociation of benzylpyridinium "thermometer" ions is widely used to calibrate the internal energy of ions produced in mass spectrometry. The fragmentation mechanism is usually believed to yield a benzylium cation, although recent studies suggest the possibility of a rearrangement leading to the tropylium isomer, which would compromise the accuracy of energy calibrations. In this study, we used IRMPD spectroscopy to probe the dissociation pathways of the p-(tert-butyl)benzylpyridinium ion. Our results show that the formation of both benzylium and tropylium products is feasible depending on the activation regime and on the reaction time scale. Varying the trapping delays in the hexapole gives insight into a rearrangement mechanism occurring through consecutive reactions with an isomerization from benzylium to tropylium. Our work provides experimental validations for the established calibration procedure and highlights the adequacy of IRMPD spectroscopy to qualitatively resolve gas-phase rearrangement kinetics.

Characteristics of positive and negative secondary ions emitted from [Formula: see text] and [Formula: see text] impacts

The current limitation for SIMS analyses is insufficient secondary ion yields, due in part to the inefficiency of traditional primary ions. Massive gold clusters are shown to be a route to significant gains in secondary ion yields relative to other commonly used projectiles. At an impact energy of 520 keV, [Formula: see text] is capable of generating an average of greater than ten secondary ions per projectile, with some impact events generating >100 secondary ions. The capability of this projectile for signal enhancement is further displayed through the observation of up to seven deprotonated molecular ions from a single impact on a neat target of the model pentapeptide leu-enkephalin. Positive and negative spectra of leu-enkephalin reveal two distinct emission regimes responsible for the emission of either intact molecular ions with low internal energies or small fragment species. The internal energy distribution for this projectile is measured using a series of benzylpyridinium salts and compared with the small polyatomic projectile [Formula: see text] at 110 keV as well as distributions previously reported for electrospray ionization and fast atom bombardment. These results show that [Formula: see text] offers high secondary ion yields not only for small fragment ions, e.g. CN-, typically observed in SIMS analyses, but also for characteristic molecular ions. For the leu-enkephalin example, the yields for each of these species are greater than unity.

Modification of the Nonanalytic Equation of State for the Limit of Low Densities

As described in previous reports, this equation is constrained to the liquid-vapor coexistence boundary. Integration of the "thermodynamic equation of state" along isotherms involves a term for the compressibility factor of saturated vapor in the limit of low densities, which in previous work was not adequately defined. The present, brief report assumes familiarity with previous work, and presents a solution for the problem, which is to describe saturated-vapor densities in terms of the compressibility factor for saturated vapor, utilizing a given, vapor-pressure equation.

Thermodynamic Properties of Fluid Oxygen at Temperatures to 250 K and Pressures to 350 Atmospheres on Isochores at 1.3 to 3.0 Times Critical Density

The starting point for these calculations is liquid oxygen at the triple point. An analytical formula is used for specific heats of saturated liquid along the coexistence path to obtain internal energies and entropies of the saturated liquid. With these initial values, the calculations next are made as a function of temperature along isochores, using an "equation of state" for the specific heats C v (ρ, T) in the single-phase domain. Enthalpies are obtained by adding P v to the internal energies. Results are tabulated at uniform densities and temperatures. Based on uncertainties of one percent in the specific heat data, the uncertainty of thermal properties also is taken to be 1 percent.