Search results for "Borates"
showing 10 items of 14 documents
Performance of amines as silanol suppressors in reversed-phase liquid chromatography
2016
In reversed-phase liquid chromatography, cationic basic compounds yield broad and asymmetrical peaks, as a result of their ionic interaction with the anionic free silanol groups present in the silica-based stationary phases (commonly derivatised with C18 groups). A simple way to improve the peak shape is the addition to the hydro-organic mobile phase of a reagent (usually called additive) with cationic character. This associates with the stationary phase to prevent the access of analytes to the free silanol groups. Cationic additives may interact electrostatically with the anionic silanols. The hydrophobic region of the additive may also associate with the alkyl chains bound to the stationa…
Suitability of 1-hexyl-3-methylimidazolium ionic liquids for the analysis of pharmaceutical formulations containing tricyclic antidepressants
2018
Abstract The reversed-phase chromatographic behaviour of six tricyclic antidepressants (amitryptiline, clomipramine, doxepin, imipramine, nortryptiline and maprotiline) was examined in this work with acetonitrile-water mobile phases, in the absence and presence of the ionic liquids 1-hexyl-3-methylimidazolium chloride and 1-hexyl-3-methylimidazolium tetrafluoroborate, which have interesting features for the separation of basic compounds, in terms of peak shape combined with reduced retention. Tricyclic antidepressants are low polarity drugs that strongly associate to the alkyl chains of conventional stationary phases. They are also positively charged in the usual working pH range (2–8) in r…
Borate-driven gatelike scaffolding using mesoporous materials functionalised with saccharides.
2009
We report the development of an MCM-41 mesoporous support that is functionalised with saccharides at the pore outlets and contains the dye [Ru(bipy)(3)](2+) in the pores (solid S1; bipy = 2,2'-bipyridyl). For this hybrid system, the inhibition of mass transport of the dye from the pore voids to the bulk solution in the presence of borate is demonstrated in water at neutral pH. The formation of the corresponding boroester derivative is related to the selective reaction of borate with the appended saccharides. This control is selective and only anion borate, among several anions and cations, can act as a molecular tap and inhibit the delivery of the entrapped guest. Additionally, the S1-borat…
1-Hexyl-3-methyl imidazolium tetrafluoroborate: an efficient column enhancer for the separation of basic drugs by reversed-phase liquid chromatograph…
2012
Abstract Ionic liquids are dual modifiers composed by a large anion and a large cation, which interact with both the hydrophobic alkyl-bonded phase and the anionic residual silanols in C18 columns. The deactivation of the silanol groups has important implications on the chromatographic analysis of basic drugs, being the improvement of peak profiles and shorter retention times the most noticeable features. However, other characteristics as selectivity or resolution are not usually considered, or are only examined for selected chromatographic conditions. In this work, the effect of the addition of the ionic liquid 1-hexyl-3-methyl imidazolium tetrafluoroborate to acetonitrile–water mixtures i…
Gaining insight in the behaviour of imidazolium-based ionic liquids as additives in reversed-phase liquid chromatography for the analysis of basic co…
2015
In reversed-phase liquid chromatography in the absence of additives, cationic basic compounds give rise to broad and asymmetrical peaks as a result of ionic interactions with residual free silanols on silica-based stationary phases. Ionic liquids (ILs), added to the mobile phase, have been suggested as alternatives to amines to block the activity of silanols. However, the dual character of ILs should be considered: both cation and anion may be adsorbed on the stationary phase, thereby creating a double asymmetrical layer positively or negatively charged, depending on the relative adsorption of both ions. In this work, a study of the performance of six imidazolium-based ILs (the chlorides an…
Evaluation of molecular mass and tacticity of polyvinyl alcohol by non-equilibrium capillary electrophoresis of equilibrium mixtures of a polymer and…
2011
Non-equilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) has been used to characterize polyvinyl alcohol (PVA). Commercial PVA samples with different molecular masses, from M(w)=15 up to 205 kDa, were used. According to the (13)C NMR spectra, the samples also differed in tacticity (stereoregularity). Mixtures of PVA and the anionic azo-dye Congo Red (CR) were injected in the presence of a borate buffer. The electropherograms gave a band and a peak due to the residual PVA-CR complex and the excess dye, respectively, plus a superimposed exponential decay due to the partial dissociation of the complex during migration. The stoichiometry of the PVA-CR complex, q=[monomer]/[dye…
Study of aromatic nucleophilic substitution with amines on nitrothiophenes in room-temperature ionic liquids: are the different effects on the behavi…
2006
The kinetics of the nucleophilic aromatic substitution of some 2-L-5-nitrothiophenes (para-like isomers) with three different amines (pyrrolidine, piperidine, and morpholine) were studied in three room-temperature ionic liquids ([bmim][BF4], [bmim][PF6], and [bm(2)im][BF4], where bmim = 1-butyl-3-methylimidazolium and bm(2)im = 1-butyl-2,3-dimethylimidazolium). To calculate thermodynamic parameters, a useful instrument to gain information concerning reagent-solvent interactions, the reaction was carried out over the temperature range 293-313 K. The reaction occurs faster in ionic liquids than in conventional solvents (methanol, benzene), a dependence of rate constants on amine concentration…
Optical characterization of YCa4O(BO3)3 and Nd:YCa4O(BO3)3 crystals
2007
International audience; We report a complete optical characterization of YCa4O(BO3)3 and Nd:YCa4O(BO3)3 crystals. We studied the relative orientation between the dielectric and the crystallographic frames as a function of the wavelength and performed accurate phase-matching angles measurements for second harmonic generation, using a single crystal cut as a sphere. We also recorded polarized luminescence spectra of Nd:YCOB along the principal axes of the dielectric frame. For both crystals, we measured the gray-tracking and the thermo-optic properties as a function of temperature and wavelength using oriented slabs. Finally, we measured all their dielectric and electro-optic coefficients, as…
Symmetric Fluoroborate and its Boron Modification: Crystal and Electronic Structures
2019
Four boron-carrying molecules were synthesized and purified. These were found to be (a) relatively neutral with respect to the parent BF derivative and (b) functionalized by donor&ndash
The role of the dual nature of ionic liquids in the reversed-phase liquid chromatographic separation of basic drugs.
2010
The cationic nature of basic drugs gives rise to broad asymmetrical chromatographic peaks with conventional C18 columns and hydro-organic mixtures, due to the ionic interaction of the positively charged solutes with the free silanol groups on the alkyl-bonded reversed-phase packing. Ionic liquids (ILs) have recently attracted some attention to reduce this undesirable silanol activity. ILs are dual modifiers (with a cationic and anionic character), which means that both cation and anion can be adsorbed on the stationary phase, giving rise to interesting interactions with the anionic free silanols and the cationic basic drugs. A comparative study of the performance of four imidazolium-based I…