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See detailNon-thermal radiation from a runaway early-type star
del Valle, M.; Romero, G.E.; De Becker, Michaël ULg

in AIP Conference Proceedings (2012, December), 1505

HD 195592 is an O-type supergiant star, known as a well-established runaway. Recently, a Fermi γ-ray source (2FGL J2030.7+4417) with a position compatible with that of HD 195592 has been reported. Our ... [more ▼]

HD 195592 is an O-type supergiant star, known as a well-established runaway. Recently, a Fermi γ-ray source (2FGL J2030.7+4417) with a position compatible with that of HD 195592 has been reported. Our goal is to explore a scenario where HD 195592 is the counterpart of the Fermi γ-ray source. The high-energy emission would be inverse Compton radiation produced in the bowshock of the runaway star. We calculate relativistic particle energy losses and the resulting radiation from the bowshock of HD 195592 and show that the latter is compatible with the detected γ-ray emission. We conclude that the Fermi source 2FGL J2030.7+4417 might be produced, under some energetic assumptions, by inverse Compton up-scattering of infrared photons from locally heated dust. HD 195592 might therefore be the very first object detected belonging to the category of γ-ray emitting runaway massive stars, whose existence has been recently predicted. [less ▲]

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See detailNon-thermal radio emission from colliding-wind binaries: modelling Cyg OB2 No. 8A and No. 9
Volpi, Delia; Blomme, Ronny; De Becker, Michaël ULg et al

in Neiner, Coralie; Wade, G.; Meynet, G. (Eds.) et al Active OB stars: structure, evolution, mass loss and critical limits (2011, July 01)

Some OB stars show variable non-thermal radio emission. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated to high energies. The electron acceleration occurs ... [more ▼]

Some OB stars show variable non-thermal radio emission. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated to high energies. The electron acceleration occurs at strong shocks created by the collision of radiatively-driven stellar winds in binary systems. Here we present results of our modelling of two colliding wind systems: Cyg OB2 No. 8A and Cyg OB2 No. 9. [less ▲]

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See detailNon-thermal radio emission from O-type stars. I. HD168112
Blomme, Ronny; Van Loo, S.; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2005), 436(3), 1033-1040

We present a radio lightcurve of the O5.5 III(f(+)) star HD 168112, based on archive data from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). The fluxes show considerable ... [more ▼]

We present a radio lightcurve of the O5.5 III(f(+)) star HD 168112, based on archive data from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). The fluxes show considerable variability and a negative spectral index, thereby confirming that HD 168112 is a non-thermal radio emitter. The non-thermal radio emission is believed to be due to synchrotron radiation from relativistic electrons that have been Fermi accelerated in shocks. For HD 168112, it is not known whether these shocks are due to a wind-wind collision in a binary system or to the intrinsic instability of the stellar wind driving mechanism. Assuming HD 168112 to be a single star, our synchrotron model shows that the velocity jump of the shocks should be very high, or there should be a very large number of shocks in the wind. Neither of these is compatible with time-dependent hydrodynamical calculations of O star winds. If, on the other hand, we assume that HD 168112 is a binary, the high velocity jump is easily explained by ascribing it to the wind-wind collision. By further assuming the star to be an eccentric binary, we can explain the observed radio variability by the colliding-wind region moving in and out of the region where free-free absorption is important. The radio data presented here show that the binary has a period of between one and two years. By combining the radio data with X-ray data, we find that the most likely period is similar to 1.4 yr. [less ▲]

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See detailNon-thermal radio emission from O-type stars. II. HD167971
Blomme, Ronny; De Becker, Michaël ULg; Runacres, M. C. et al

in Astronomy and Astrophysics (2007), 464(2), 701-148

HD 167971 is a triple system consisting of a 3.3-day eclipsing binary (O5- 8 V + O5- 8 V) and an O8 supergiant. It is also a well known non-thermal radio emitter. We observed the radio emission of HD ... [more ▼]

HD 167971 is a triple system consisting of a 3.3-day eclipsing binary (O5- 8 V + O5- 8 V) and an O8 supergiant. It is also a well known non-thermal radio emitter. We observed the radio emission of HD 167971 with the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). By combining these data with VLA archive observations we constructed a radio lightcurve covering a 20-yr time-range. We searched for, but failed to find, the 3.3-day spectroscopic period of the binary in the radio data. This could be due to the absence of intrinsic synchrotron radiation in the colliding-wind region between the two components of the eclipsing binary, or due to the large amount of free-free absorption that blocks the synchrotron radiation. We are able to explain many of the observed characteristics of the radio data if the non-thermal emission is produced in a colliding-wind region between the supergiant and the combined winds of the binary. Furthermore, if the system is gravitationally bound, the orbital motion occurs over a period of similar to 20 years or longer, as suggested by the long-term variability in the radio data. We argue that the variability is due to the free-free absorption that changes with orbital phase or may also in part be due to changes in separation, should the orbit be eccentric. [less ▲]

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See detailNon-thermal radio emission from O-type stars. IV. Cygnus OB2 No. 8A
Blomme, R.; De Becker, Michaël ULg; Volpi, D. et al

in Astronomy and Astrophysics (2010), 519

Context. Several early-type colliding-wind binaries are known to emit synchrotron radiation due to relativistic electrons, which are most probably accelerated by the Fermi mechanism. By studying such ... [more ▼]

Context. Several early-type colliding-wind binaries are known to emit synchrotron radiation due to relativistic electrons, which are most probably accelerated by the Fermi mechanism. By studying such systems we can learn more about this mechanism, which is also relevant in other astrophysical contexts. Colliding-wind binaries are furthermore important for binary frequency determination in clusters and for understanding clumping and porosity in stellar winds. Aims: We study the non-thermal radio emission of the binary Cyg OB2 No. 8A, to see if it is variable and if that variability is locked to the orbital phase. We investigate if the synchrotron emission generated in the colliding-wind region of this binary can explain the observations and we verify that our proposed model is compatible with the X-ray data. Methods: We use both new and archive radio data from the Very Large Array (VLA) to construct a light curve as a function of orbital phase. We also present new X-ray data that allow us to improve the X-ray light curve. We develop a numerical model for the colliding-wind region and the synchrotron emission it generates. The model also includes free-free absorption and emission due to the stellar winds of both stars. In this way we construct artificial radio light curves and compare them with the observed one. Results: The observed radio fluxes show phase-locked variability. Our model can explain this variability because the synchrotron emitting region is not completely hidden by the free-free absorption. In order to obtain a better agreement for the phases of minimum and maximum flux we need to use stellar wind parameters for the binary components which are somewhat different from typical values for single stars. We verify that the change in stellar parameters does not influence the interpretation of the X-ray light curve. Our model has trouble explaining the observed radio spectral index. This could indicate the presence of clumping or porosity in the stellar wind, which - through its influence on both the Razin effect and the free-free absorption - can considerably influence the spectral index. Non-thermal radio emitters could therefore open a valuable pathway to investigate the difficult issue of clumping in stellar winds. [less ▲]

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See detailThe Non-thermal Radio Emitter HD 93250 Resolved by Long Baseline Interferometry
Sana, H.; Le Bouquin, J.-B.; De Becker, Michaël ULg et al

in Astrophysical Journal Letters (2011), 740

As the brightest O-type X-ray source in the Carina nebula, HD 93250 (O4 III(fc)) is X-ray overluminous for its spectral type and has an unusually hard X-ray spectrum. Two different scenarios have been ... [more ▼]

As the brightest O-type X-ray source in the Carina nebula, HD 93250 (O4 III(fc)) is X-ray overluminous for its spectral type and has an unusually hard X-ray spectrum. Two different scenarios have been invoked to explain its X-ray properties: wind-wind interaction and magnetic wind confinement. Yet, HD 93250 shows absolutely constant radial velocities over timescales of years suggesting either a single star, a binary system seen pole-on view or a very long period, and/or highly eccentric system. Using the ESO Very Large Telescope Interferometer, we resolved HD 93250 as a close pair with similar components. We measured a near-infrared flux ratio of 0.8 ± 0.1 and a separation of (1.5 ± 0.2) × 10-3 arcsec. At the distance of Carina, this corresponds to a projected physical distance of 3.5 AU. While a quantitative investigation would require a full characterization of the orbit, the binary nature of HD 93250 allows us to qualitatively explain both its X-ray flux and hardness and its non-thermal radio emission in the framework of a colliding wind scenario. We also discuss various observational biases. We show that, due to line blending of two similar spectral components, HD 93250 could have a period as short as 1 to several years despite the lack of measurable radial velocity variations. [less ▲]

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See detailA non-traumatic case of intracranial haemorrhage in a horse
Verwilghen, Denis ULg; Van Galen, Gaby ULg; Peters, Fabrice et al

Poster (2006, August)

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See detailThe non-trivial dispersion of Y2BaCuO5 particles trapped in the YBa2Cu3O7-x crystal matrix
Vandewalle, Nicolas ULg; Pirard, E.; Cloots, Rudi ULg et al

in Philosophical Magazine Letters (1998), 77(5), 301-306

Micrographs of melt-textured YBa2Cu3O7-x/Y2BaCuO5 (123/211) have been digitized. Through image analysis, we point out that the dispersion of the 211 particles is highly inhomogeneous in the melt and in ... [more ▼]

Micrographs of melt-textured YBa2Cu3O7-x/Y2BaCuO5 (123/211) have been digitized. Through image analysis, we point out that the dispersion of the 211 particles is highly inhomogeneous in the melt and in the 123 crystal matrix. Indeed, free 211 particle regions and 211 aggregates are observed. The distribution laws are given. Moreover, the dispersions of 211 particles in the melt and those trapped in the crystal matrix are quite different. We point out that this difference cannot be explained solely by the partial dissolution of the 211 particles during the growth process. [less ▲]

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See detailNon-uniform adaptive vertical grids for 3D numerical ocean models
Hofmeister, R.; Burchard, H.; Beckers, Jean-Marie ULg

in Ocean Modelling (2010), 33

A new strategy for the vertical gridding in terrain-following 3D ocean models is presented here. The vertical grid adaptivity is partially given by a vertical diffusion equation for the vertical layer ... [more ▼]

A new strategy for the vertical gridding in terrain-following 3D ocean models is presented here. The vertical grid adaptivity is partially given by a vertical diffusion equation for the vertical layer positions, with diffusivities being proportional to shear, stratification and distance from the boundaries. In the horizontal, the grid can be smoothed with respect to z-levels, grid layer slope and density. Lagrangian tendency of the grid movement is supported. The adaptive terrain-following grid can be set to be an Eulerian–Lagrangian grid, a hybrid r–q or r–z grid and combinations of these with great flexibility. With this, internal flow structures such as thermoclines can be well resolved and followed by the grid. A set of idealised examples is presented in the paper, which show that the introduced adaptive grid strategy reduces pressure gradient errors and numerical mixing significantly. The grid adaption strategy is easy to implement in various types of terrain-following ocean models. The idealised examples give evidence that the adaptive grids can improve realistic, long-term simulations of stratified seas while keeping the advantages of terrain-following coordinates. [less ▲]

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See detailNon-uniform adaptive vertical grids in one-dimensional numerical ocean models
Burchard, Hans; Beckers, Jean-Marie ULg

in Ocean Modelling (2004), 6(1), 51-81

It is demonstrated in this paper how the concept of general vertical coordinates can be exploited for constructing adaptive grids in primitive equation ocean models. The term adaptive is used here in the ... [more ▼]

It is demonstrated in this paper how the concept of general vertical coordinates can be exploited for constructing adaptive grids in primitive equation ocean models. The term adaptive is used here in the sense of coordinate iso-surfaces which follow certain internal structures of the flow in such a way that higher vertical resolution is obtained in locations where vertical gradients are large. The internal structures considered here are shear and stratification. In this paper, one-dimensional models are applied in order to demonstrate the ability of such grid adaptation methods to follow internal structures even in flow situations dominated by vertical mixing processes. Here, a variational approach is considered for the generation of grids which results in a diffusion equation for the vertical coordinate. The method is tested for five different idealised and realistic scenarios with the result that the discretisation error can be significantly reduced in comparison to equidistant Cartesian grids. Some recommendations for extending these methods for three-dimensional models are given at the end of this paper. (C) 2003 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailNon-uniqueness of the natural and projectively equivariant quantization
Radoux, Fabian ULg

in Journal of Geometry & Physics (2008), 58

In [C. Duval, V. Ovsienko, Projectively equivariant quantization and symbol calculus: Noncommutative hypergeometric functions, Lett. Math. Phys. 57 (1) (2001) 61–67], the authors showed the existence and ... [more ▼]

In [C. Duval, V. Ovsienko, Projectively equivariant quantization and symbol calculus: Noncommutative hypergeometric functions, Lett. Math. Phys. 57 (1) (2001) 61–67], the authors showed the existence and the uniqueness of a sl(m+1,R)-equivariant quantization in non-critical situations. The curved generalization of the sl(m+1,R)-equivariant quantization is the natural and projectively equivariant quantization. In [M. Bordemann, Sur l’existence d’une prescription d’ordre naturelle projectivement invariante (submitted for publication). math.DG/0208171] and [Pierre Mathonet, Fabian Radoux, Natural and projectively equivariant quantizations by means of Cartan connections, Lett. Math. Phys. 72 (3) (2005) 183–196], the existence of such a quantization was proved in two different ways. In this paper, we show that this quantization is not unique. [less ▲]

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See detailNon-visual brain sensitivity to light in aging
Daneault, V; Vandewalle, Gilles ULg; Hébert, M et al

Poster (2011, March)

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See detailNonadiabatic observables in main sequence delta Scuti stars
Moya, A.; Garrido, R.; Dupret, Marc-Antoine ULg

in IAU Colloq. 193: Variable Stars in the Local Group (2004, May 01)

Using a theoretical nonadiabatic pulsation model, phase differences and amplitude ratios between the relative effective temperature variation and the relative radial displacement have been calculated ... [more ▼]

Using a theoretical nonadiabatic pulsation model, phase differences and amplitude ratios between the relative effective temperature variation and the relative radial displacement have been calculated. These quantities, when compared with photometric observations in different colors, provide an efficient instrument for mode identification, the first step to understand the internal structure of the stars. The theoretical results presented in this paper show a dependence for delta Scuti stars on the mixing length parameter alpha used to treat the convection using the standard Mixing Length Theory. The nonadiabatic pulsational code developed here includes the pulsation atmosphere interaction as described by Dupret et al. (2002). The equilibrium models are provided by the CESAM evolutionary code, where a complete reconstruction of non-grey atmospheres (Kurucz models) is included. [less ▲]

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See detailNONADIABATIC UNIMOLECULAR REACTIONS .2. ISOTOPE EFFECTS ON THE KINETIC-ENERGY RELEASE
Remacle, Françoise ULg; Dehareng, Dominique ULg; Lorquet, Jean-Claude ULg

in Journal of Physical Chemistry (1988), 92(16), 4784-4787

This paper investigates the isotope effect that occurs when XOCO+ ions dissociate into XOC+ + 0 on a microsecond time scale (X = H or D). The reaction mechanism involves an electronic spin-forbidden ... [more ▼]

This paper investigates the isotope effect that occurs when XOCO+ ions dissociate into XOC+ + 0 on a microsecond time scale (X = H or D). The reaction mechanism involves an electronic spin-forbidden predissociation between a stable singlet state and a repulsive triplet. Application of the statistical equations developed in the previous paper shows that, at a given energy, the predissociation rate constant is consistently smaller for DOCO’ than for HOCO+. Therefore, the internal energy necessary to bring about dissociation of the hydrogenated compound with a given rate constant is always lower than that of the deuteriated compound by a quantity AE* which is found to be equal to ca. 0.050 eV when k = lo6 s-l and to ca 0.020 eV for k = lo3 s-1. As a result, the excess energy which is released as kinetic energy carried by the fragments is substantially greater for the deuteriated than for the hydrogenated compound. This accounts for experiments which indicate that, in the microsecond time scale, DOCO’ gives rise to a dished metastable peak whereas the corresponding signal for HOCO’ is simply Gaussian. [less ▲]

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See detailNonadiabatic Unimolecular Reactions of Polyatomic Molecules
Desouter-Lecomte, Michèle ULg; Dehareng, Dominique ULg; Leyh-Nihant, Brigitte et al

in Journal of Physical Chemistry (1985), 89

The nonadiabatic couplings which arise when two potential energy surfaces of a polyatomic molecule get close in energy can be classified as follows: (A) avoided crossings, (B) genuine intersections (Jahn ... [more ▼]

The nonadiabatic couplings which arise when two potential energy surfaces of a polyatomic molecule get close in energy can be classified as follows: (A) avoided crossings, (B) genuine intersections (Jahn-Teller and conical), (C) glancing intersections (Renner-Teller interactions). The characteristics of the potential energy surfaces in the adiabatic and diabatic representations are discussed for each case. The three coupling cases differ in the structure of the Hamiltonian matrix. When the latter is written in the diabatic representation, it is meaningful to retain the leading term only in its power series expansion. This gives rise to a so-called minimum-order model which is found to be surprisingly accurate (at least in a restricted zone of nuclear coordinates) when compared to the results of ab initio calculations. The characteristic features of each coupling case can only be understood in a two-dimensional configuration space, Le., when two nuclear degrees of freedom, often with different symmetry properties, are explicitly considered. A simple expression of the nonadiabatic transition probability between two electronic states can be worked out in the framework of the minimum-order models. Two-dimensional extensions of the Landau-Zener formula are obtained, which can be used to study the consequences of the anisotropic properties of the coupling. In the case of avoided crossings, only nuclear trajectories having a well-defined direction are able to bring about surface hopping, wheras there exists two active degrees of freedom for conical intersections. Hence, nonadiabatic processes which are controlled by genuine intersections are expected to take place faster than those controlled by avoided crossings. [less ▲]

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See detailNonalcoholic steatohepatitis and insulin resistance: interface between gastroenterologists and endocrinologists.
Scheen, André ULg; Luyckx, Françoise ULg

in Acta Clinica Belgica (2003), 58(2), 81-91

Nonalcoholic steatohepatitis (NASH), along with other forms of nonalcoholic fatty liver disease, is an increasingly common clinico-pathological syndrome. It is frequently associated with obesity ... [more ▼]

Nonalcoholic steatohepatitis (NASH), along with other forms of nonalcoholic fatty liver disease, is an increasingly common clinico-pathological syndrome. It is frequently associated with obesity, especially visceral fat, and type 2 diabetes, and is intimately related to markers of the insulin resistance syndrome. Both the prevalence and the severity of liver steatosis are related to body mass index, waist circumference, hyperinsulinaemia, hypertriglyceridemia and impaired glucose tolerance. The pathophysiology of NASH involves two steps: 1) insulin resistance, which causes steatosis; 2) and oxidative stress, which produces lipid peroxidation and activates inflammatory cytokines. The identification of subjects who may progress from fatty liver to NASH, and from NASH to fibrosis/cirrhosis is an important clinical challenge as well as the finding of appropriate therapy that could prevent such deleterious process. Substantial weight loss is accompanied by a marked attenuation of insulin resistance and related metabolic syndrome and, concomitantly, by an important regression of liver steatosis in most patients, although mild inflammation may be detected in some subjects. Thus, NASH may be considered as another disease of affluence, as is the insulin resistance syndrome and perhaps being part of it. [less ▲]

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See detailNonaqueous capillary electrophoresis method for the enantiomeric purity determination of S-timolol using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin: validation using the accuracy profile strategy and estimation of uncertainty.
Marini Djang'Eing'A, Roland ULg; Servais, Anne-Catherine ULg; Rozet, Eric ULg et al

in Journal of Chromatography. A (2006), 1120(1-2), 102-11

Nonaqueous capillary electrophoresis (NACE) was successfully applied to the enantiomeric purity determination of S-timolol maleate using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD ... [more ▼]

Nonaqueous capillary electrophoresis (NACE) was successfully applied to the enantiomeric purity determination of S-timolol maleate using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) as chiral selector. With a background electrolyte made up of a methanolic solution of 0.75 M formic acid, 30 mM potassium camphorsulfonate and containing 30 mM HDMS-beta-CD, the determination of 0.1% of R-timolol in S-timolol could be performed with an enantiomeric resolution of 8.5. Pyridoxine was selected as internal standard. The NACE method was then fully validated by applying a novel strategy using accuracy profiles. It is based on beta-expectation tolerance intervals for the total measurement error which includes trueness and intermediate precision. The uncertainty of measurements derived from beta-expectation tolerance intervals was estimated at each concentration level of the validation standards. To confirm the suitability of the developed and validated method, several real samples of S-timolol maleate containing R-timolol maleate at different concentrations were analysed and the results were compared to those obtained by liquid chromatography. [less ▲]

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See detailNonaqueous capillary electrophoretic behavior of 2-aryl propionic acids in the presence of an achiral ionic liquid - A chemometric approach
Francois, Yannis; Varenne, Anne; Juillerat, Emilie et al

in Journal of Chromatography. A (2007), 1138(1-2), 268-275

Ionic liquids (ILs) appear really attractive as electrolyte additives in nonaqueous capillary electrophoresis (NACE). These salts may offer new possibilities of interactions to modulate analyte effective ... [more ▼]

Ionic liquids (ILs) appear really attractive as electrolyte additives in nonaqueous capillary electrophoresis (NACE). These salts may offer new possibilities of interactions to modulate analyte effective mobilities. The presence of 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM NTf2) in acetonitrile/alcohol background electrolytes (BGEs) was investigated in this work. The aim of this study was to elucidate the influence of the IL concentration on the electrophoretic behavior of four arylpropionic acids and to identify the interactions between the analytes and the 1L cation. The influence on mobility of the IL concentration, the nature and the proportion of the organic solvents, and the concentration of the ionic components of the BGE was first studied by a univariate approach. A four-factor D-optimal experimental design was then applied to provide a deeper insight into analyte interaction with IL cation present both free in BGE and adsorbed onto the capillary wall. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailNonaqueous electrokinetic chromatography-electrospray ionization mass spectrometry using anionic cyclodextrins
Mol, Roelof; Servais, Anne-Catherine ULg; Fillet, Marianne ULg et al

in Journal of Chromatography. A (2007), 1159(1-2), 51-57

The set-up of an on-line method for coupling nonaqueous electrokinetic chromatography (NAEKC) and electrospray ionization mass spectrometry (ESI-MS) is presented. It allows the use of the single-isomer ... [more ▼]

The set-up of an on-line method for coupling nonaqueous electrokinetic chromatography (NAEKC) and electrospray ionization mass spectrometry (ESI-MS) is presented. It allows the use of the single-isomer derivative anionic cyclodextrins heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) and heptakis(2.3-di-O-acetyl-6-O-sulfo)-beta-cyclodextrin (HDAS-beta-CD) for chiral and achiral separations of positively charged analytes. The effect of the cyclodextrins (CDs) on the MS signal intensities of model compounds was studied. When a voltage is applied over the CE capillary, the overall mobility of the CDs is towards the inlet vial preventing CDs from entering the ion source. However, the sodium counter ions of the CDs still enter the ion source and appeared to cause ionization suppression. Nevertheless, significant analyte signals could still be detected with detection limits in the sub-mu g/ml. System parameters such as sheath liquid composition and flow rate, nebulizing gas pressure, capillary position in the sprayer and the drying gas flow and temperature were studied and optimized. The selection of a relatively low nebulizing gas pressure appeared to be important to achieve optimum sensitivity. The chiral selectivity of the NAEKC-ESI-MS system could be improved by addition of camphorsulfonate to the background electrolyte. Using mixtures of drugs and drug-related compounds, the NAEKC-ESI-MS system is shown to offer potential for (chiral) drug profiling. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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