Ethanol splitting in bipolar membranes: Evidence from NMR analysis

Bipolar membranes were reported to split alcohol into alkoxide ions and H⁺; however, there is no direct evidence for ethanol splitting, i.e., the existence of ethoxide ions. This work uses ethanol for alcohol splitting test and ¹H NMR for the identification of ethoxide ions. According to the spectra analysis, the chemical shifts of proton H, δ 3.736–3.666 (q, 2H) and δ 1.255–1.209 (t, 3H) can only be ascribed to CH₃CH₂O⁻. Therefore, this work first proves ethanol splitting in bipolar membranes by detecting the existence of sodium ethoxide. To further extend the application of electrodialysis to non-aqueous systems (as in organic synthesis), membranes of better solvent-resistance are needed to be developed.     

Enantioselective Analyses of Antihistaminic Drugs by High-Performance Liquid Chromatography

High-performance liquid chromatographic methods have been developed for stereoselective separations of terfenadine and its active metabolite fexofenadine. Satisfactory enantioseparations of racemic terfenadine were achieved on a Chiralcel column by normal phase elution. Analysis of racemic fexofenadine, as such, took a very long time and achieved poor enantioselectivity on this column; nevertheless, the analyte when derivatised with diazomethane was well resolved. Racemic fexofenadine was also derivatised using a chiral agent: R-(+)-1-phenylethylisocyanate and subjected to achiral LC on a reversed-phase analytical column. Complete enantioseparations were achieved in short analysis times; excess reagent eluted before the diastereoisomeric pair and did not interfere.Part of this work was presented at the 10^th International Meeting on Recent Developments in Pharmaceutical Analysis RDPA03, Cogne, Valle d Aosta, Italy. June 28–July 1, 2003.     

Steady and dynamic shear properties of non-aqueous drag-reducing polymer solutions

The steady and dynamic shear properties of two non-aqueous drag-reducers (a medium molecular weight polyisobutylene and a commercial organic drag-reducer) in kerosene solutions over a wide range of temperature and concentration were presented. The intrinsic and zero-shear viscosity results were used to identify the concentrate regimes of these solutions. A characteristic time constant λ₀, which was based on the spring-bead model for dilute solutions, was employed as the scaling parameter for both steady-shear and dynamic data over a wide range of concentration and temperature. The inadequacy of the Graessley reduced-variable method in the dilute region was illustrated. The shear-thinning behaviour of these polymer solutions could be described by the Carreau model. The dynamic data followed the Zimm and Rouse-like behaviour in the low and high frequency limits. The Cox-Merz rule was obeyed in the low shear rate and frequency regions. The Carreau and the zero-frequency Maxwell time constants appeared to be related to λ₀ by a constant factor over a wide range of polymer concentrations. The finding provides a method for extrapolating viscoelastic information into the drag reduction regime, and could be useful for interpretation of drag reduction results.     

Lower consolute temperature in a non-aqueous surfactant system

The phase behaviour of the system triethylene glycol dodecyl ether/formamide has been investigated at varying temperatures. The system has a lower consolute temperature (L.C.T.) at 16 °C for a critical concentration 10 w% surfactant. The addition of water lowers the L.C.T. and addition of charged surfactant raises it.     

Ionic liquids as acid/base buffers in non-aqueous solvents for homogeneous catalysis: A case of selective hydrogenation of olefins and unsaturated aldehyde catalyzed by ruthenium complexes

We present a novel approach to tune acidity/basicity in non-aqueous and low-water media by using a class of ionic liquids (ILs) with buffering characteristics, which was readily synthesized by the reaction of 1-alkyl-3-methylimidazolium hydroxide ([RMIM]OH) base moieties with a serials of binary or polybasic acids and defined as ionic liquid-buffers (IL-buffers). We have performed controlled experiments of hydrogenation of olefins and trans-cinnamaldehyde, catalyzed by [RuCl₂(PPh₃)₃] in non-aqueous media such as DMF and ILs in the presence of IL-buffers. Remarkable buffer dependence of the formation and catalytic behavior of ruthenium hydrides were evidenced by the kinetic studies and NMR measurements. The hydride [RuHCl(PPh₃)₃], being favorably formed in the presence of the IL-buffer with lower log₁₀([Base]/[Acid]), exhibited higher activity in the reduction of the CC bond against the carbonyl functionality of trans-cinnamaldehyde. While the hydride [RuH₄(PPh₃)₃], being preponderantly formed in the presence of the IL-buffer with higher log₁₀([Base]/[Acid]) showed activity and higher selectivity towards the CO reduction. Consequently, the hydrogenation performance of olefins and trans-cinnamaldehyde in non-aqueous system could be adjusted by adding the different IL-buffers. It is envisioned that the ability of IL-buffers to alter and precisely control the catalytic active species in non-aqueous or low-water systems might find appreciable applications for both fundamental studies and syntheses where the reactions are acid/base-sensitive.     

In-drop derivatisation liquid-phase microextraction assisted by ion-pairing transfer for the gas chromatographic determination of phenolic endocrine disruptors

A novel in-drop derivatisation liquid-phase microextraction procedure with an ion-pairing agent is developed and optimised for the extraction of endocrine-disrupting chemicals. The ethyl esters of the analytes were rapidly formed in the organic drop and analysed by gas chromatography. The effects of various parameters such as rate and time of agitation, ion-pairing agent and reactant concentration, pH and temperature were studied systematically to optimise the process and bring out the locale of reaction in the organic drop. A study of the mechanistic pathways of the overall procedure is attempted leading to interesting findings and delineating important points of the kinetics and mechanism. A mechanistic model is proposed on the basis of the theory of mass transfer with chemical reaction in two liquid phases. The O-ethoxycarbonyl derivatisation appears to take place in the bulk organic phase. The system provides insight into the first reported analytical case of single-drop extraction-preconcentration-derivatisation assisted by an ion-pairing transfer and has all of the interesting facets of chemical reaction in which the role of mass transfer comes into picture.The analytical features of the method are acceptable and the overall relative standard deviations of the intra-day repeatability (n = 5) and inter-day reproducibility were <3.9% and <5.4%, respectively, for gas chromatography-mass spectrometry analyses and <4.3% and <7.1% for gas chromatography-flame ionisation detection analyses. The method was applicable to urine and surface water samples. The LODs ranged between 0.2-1.3 ng mL⁻¹ and 8.5-26.5 ng mL⁻¹ for GC/MS and GC/FID analyses, respectively.     

Non-Aqueous Assay System for Phenobarbital Using Biomimetic Bulk Acoustic Wave Sensor Based on a Molecularly Imprinted Polymer

ABSTRACT

A new biomimetic bulk acoustic wave (BAW) sensor based on a molecularly imprinted polymer (MIP) was fabricated and applied for the determination of phenobarbital The MIP was synthesized using phenobarbital as the template molecule and methacrylic acid as the functional monomer by the non-covalent method. In absolute ethanol, the sensor exhibited good selectivity and sensitivity. A linear relationship between 9.0×10^?8 M and 5.0×10^?5 M was revealed. The determination limit was 5.0×10^?8 M. In harsh chemical environments such as high temperature, organic solvent, bases, acids, etc., the sensor still exhibited long-time stability. Satisfactory results of real sample assay were obtained by the proposed method.     

Identification of naphtho [8.1.2 abc] coronene in the extract of diesel particulate matter by non-aqueous reversed-phase liquid chromatography coupled with UV multichannel detector

Summary Non-aqueous reversed-phase liquid chromatography coupled with a UV multichannel detector has been used for the identification of large polycyclic aromatic hydrocarbons in the extract from diesel engine particulate matter. The existence of naphtho[8,1,2,abc]coronene is first confirmed by this technique.