Aggregation of phosphate and 1‐tetradecyl‐3‐methylimidazolium chloride background electrolytes during micellar electrokinetic chromatography

We report the possible aggregation of phosphate and ionic liquid (1‐tetradecyl‐3‐methylimidazolium chloride) based BGEs during MEKC. After a certain transit period, the aggregates appear as a random sequence of spikes on a UV detector signal. Root mean square values of the spikes and aggregation time (T_a) were plotted against BGE concentrations. The observation suggests that MEKC is a simple and easy technique for micelle aggregation studies.     

Alkene‐ and Alkyne‐substituted Methylimidazolium Bromides: Structural Effects and Physical Properties

Several bromide salts composed of methylimidazolium cations possessing unsaturated sidechains (allyl‐, 3‐butenyl‐, propargyl‐, 2‐butynyl‐, and 2‐pentynyl‐) have been synthesized and characterized by multinuclear NMR, vibrational spectroscopy, DSC, and elemental analysis. Crystal structures of 1‐(2‐butynyl)‐3‐methylimidazolium bromide, 1‐propargyl‐3‐methylimidazolium bromide and 1‐allyl‐3‐methylimidazolium bromide, were determined.     

Efficient separation of tocopherol homologues in vegetable oil by ionic‐liquid‐based countercurrent chromatography using a non‐aqueous biphasic system

Tocopherol homologues are important fat‐soluble bioactive compounds with high nutritional value. However, it is of great challenge to separate these homologues because of their high structural similarities. In this work, ionic‐liquid‐based countercurrent chromatography was used for the separation and purification of tocopherol homologues. Conventional countercurrent chromatography and ionic‐liquid‐based countercurrent chromatography solvent systems were evaluated in respect of partition coefficient, separation factor, and stationary phase retention factor to separate these targets. Kind of ionic liquids, amount of ionic liquid, and sample amount were systematically optimized. A novel countercurrent chromatography non‐aqueous biphasic system composed of n‐hexane‐methanol‐1‐butyl‐3‐methylimidazolium chloride was established. The baseline separation of tocopherol mixtures was obtained in one cycle process. The ionic liquid played a key role in the countercurrent chromatography separation, which resulted in difference of partition behavior of individual tocopherol in the whole system through different hydrogen‐bonding affinity. Finally, n‐hexane‐methanol‐1‐butyl‐3‐methylimidazolium chloride (5:5:3, v/v) water‐free biphasic system was successfully applied to separate tocopherol homologues from vegetable oil that was not achieved beforehand. This method can be widely employed to separate many similar molecules such as tocotrienols, tocomonoenols, and marine‐derived tocopherol in food samples.     

Physicochemical studies of the cetyltrimethylammonium bromide micellar system using a bromide selective electrode

The use of the bromide selective electrode in physicochemical studies of the cationic micellar system of cetyltrimethylammonium bromide (CTAB) is described. Potentiometric methods and appropriate equations have been developed and used to determine the critical micellar concentration, the ionization degree, and the apparent ion-exchange constants of various anions (fluoride, chloride, hydroxide, acetate, nitrate, sulfate and borate). The interaction of the cationic micelles of CTAB with various species [the lipophilic reagent 1-fluoro-2,4-dinitrobenzene, the anionic succinate and the cationic tris-(hydroxymethyl)-aminomethane] was monitored through the measurement of the changes in the concentration of the free bromide counterions.     

Interfacial Synthesis,Vol. Ill,Recent Advances,Charles E. Carraher,Jr. and Jack Preston,editors, Marcel Dekker,Inc., New York and Basel, 1982, $65.00

Hydrolyses of p‐nitrophenyl picolinate (PNPP) and p‐nitrophenyl acetate (PNPA) mediated by the micellar catalytic systems of two types of cationic surfactants [cetyltrimethylammonium bromide (CTAB), Gemini dimethylene‐1,2‐bis(cetyltrimethylammonium bromide) (16‐2‐16, 2Br^?)] were investigated spectrophotometrically in the pH range of 7.0–9.0 and 25°C. Also, the effects of several kinds of additives, such as ethanol, cyclodextrins (CDs), on the hydrolytic reactions of PNPP and PNPA were studied systematically. It is noteworthy that: (1) double chain Gemini surfactant micellar system enhanced the hydrolyses of carboxylic acid esters notably compared with single chain surfactant (CTAB) micellar solutions under the same reaction conditions; (2) the apparent rate constants (k _obsd) of PNPP and PNPA hydrolyses increased with the increasing in pH values of reaction media; (3) as additives, ethanol has effect on both PNPP and PNPA hydrolyses, and moreover, the k _obsd for hydrolyses decreased with the increasing contents of ethanol (≤5%) at 25°C and pH 9.00; (4) the presence of CDs [α‐cyclodextrin (α‐CD), β‐cyclodextrin (β‐CD), γ‐cyclodextrin (γ‐CD)], as additives, showed different effects on PNPP and PNPA hydrolyses in different reaction systems.     

Ionic liquids based on imidazole for online concentration of catecholamines in capillary electrophoresis

Potential possibilities of long‐chain ionic liquids based on imidazole (1‐dodecyl‐3‐methylimidazolium chloride and 1‐cetyl‐3‐methylimidazolium chloride) for online sample concentration techniques (field‐amplified sample stacking, head‐column field‐amplified sample stacking, and sweeping) of catecholamines were studied in both capillary zone electrophoresis and micellar electrokinetic chromatography. The use of a high‐conductivity sample matrix in sweeping was found to significantly increase the separation efficiency of analyte up to 2 × 10⁶ theoretical plates per meter and remarkably reduce limits of detection for catecholamines up to 50 ng/mL. This approach was shown to be suitable for the determination of trace amounts of catecholamines in biological fluids.     

Application of Some Room Temperature Ionic Liquids in the Development of Biosensors at Carbon Film Electrodes

Two room temperature ionic liquids, 1‐butyl‐3‐methylimidazolium bistriflimide and 1‐butyl‐3‐methylimidazolium nitrate, were employed for enzyme immobilization in a new sol‐gel matrix and, for the first time, were successfully applied as electrolyte carriers in a biosensing system. The new sol‐gel matrix, based on 3‐aminopropyltrimethoxysilane and 1‐butyl‐3‐methylimidazolium bistriflimide mixtures, did not crack even after several weeks when kept dry, and exhibited similar analytical properties to aqueous sol‐gel based glucose biosensors. The linear range was up to 1.1 mM of glucose, sensitivity was 62 nA mM^?1 and the limit of detection was 28.8 μM. The optimum ionic liquid electrolyte carrier was found to be 1‐butyl‐3‐methylimidazolium nitrate, where the biosensor was made by electrodeposition of the redox mediator, poly(neutral red), and the enzyme was immobilized by cross‐linking with glutaraldehyde. The results showed that application of room temperature ionic liquids to biosensors is very promising and can be further exploited.     

On-line sample concentration in micellar electrokinetic chromatography using cationic surfactants

Two on-line sample concentration techniques, sample stacking and sweeping, were evaluated using cationic surfactants as pseudostationary phases in micellar electrokinetic chromatography. As cationic surfactant micelles, tetradecyltrimethylammonium bromide and cetyltrimethylammonium chloride were employed. About 10-fold and 1000-fold increases in detection sensitivity in terms of peak heights were observed by sample stacking and sweeping, respectively, without suppression of the electroosmotic flow. In particular, the concentration limits of detection (S/N=3) for test naphthalenesulfonic acids obtained with sweeping were from 0.96 to 0.47 ppb with UV detection without any preconcentration procedure.     

Micellar-mediated shifts of ionization constants of amino acids and peptides

The acid-base dissociation constants, K_a, of amino acids and small peptides were determined in both aqueous and micellar solutions of sodium dodecyl sulfate and cetyltrimethylammonium bromide by potentiometric and chromatographic means. The observed differences in pK_a values between micellar media and aqueous solutions ranged between 0.23 and 2.21 units. The micellar-mediated pK_a shifts can be attributed to different solute-micelle interactions, mainly hydrophobic and electrostatic forces. The implications of the change in acid-base behavior on separation selectivity in micellar liquid chromatography and micellar electrokinetic capillary chromatography are discussed.     

Molecularly imprinted SPE coupled with HPLC for the selective separation and enrichment of alkyl imidazolium ionic liquids in environmental water samples

A novel 1‐butyl‐3‐methylimidazolium chloride ionic liquid surface imprinted solid‐phase sorbent was synthesized. The as‐prepared material was characterized by SEM, Brunauer–Emmett–Teller surface area analysis and Fourier Transform IR measurements. Then its adsorption properties for alkyl imidazolium ionic liquids, including adsorption capacities, adsorption kinetics, and properties of selective separation and enrichment were studied in detail. It was shown that the ionic liquid surface imprinted polymer exhibited high selective recognition characteristics for the imidazolium chloride ionic liquids with short alkyl chains (C_nmimCl, n = 2, 4, 6, 8) and the adsorption equilibrium was achieved within 25 min. Various parameters were optimized for the 1‐butyl‐3‐methylimidazolium chloride ionic liquid surface imprinted polymer SPE column, such as flow rate, eluent solvent, selectivity, and reusability of the column. Then, the SPE column coupled with HPLC was used for the determination of alkyl imidazolium ionic liquids. Experimental results showed that the existence of their structural analogs and common concomitants in environmental matrices did not affect the enrichment of 1‐butyl‐3‐methyl imidazolium chloride ionic liquid. The average recoveries of 1‐butyl‐3‐methylimidazolium chloride ionic liquid in spiked water samples were in the range of 92.0–102.0% with the RSD lower than 5.8%.     

Investigation on the mixed micellar systems of cationic surfactants with propylene glycol and its oligomers

The effects of the addition of several propylene glycol oligomer additives on the micellar properties of the cationic mixed micelle system of cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) were investigated. Through conductivity studies, the critical micelle concentration (cmc) and counter-ion binding values were observed in the presence of the additives. A regular solution approach was employed to determine the effects of the additives on the interactions between the two surfactants to form the mixed micelles. The effects of the additives on the interaction parameter and the composition of the mixed micelles were evaluated. Excess Gibbs energy of mixing and the values of activity coefficients were also calculated and described in terms of non-ideality of the system.     

Study of the bromide oxidation by bromate in zwitterionic micellar solutions

The redox reaction Br⁻ + BrO₃⁻ has been studied in aqueous zwitterionic micellar solutions of N‐tetradecyl‐N, N‐dimethyl‐3‐ammonio‐1‐propanesulfonate, SB3‐14, and N‐hexadecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propanesulfonate, SB3‐16. A simple expression for the observed rate constant, k_obs, based on the pseudophase model, could explain the influences of changes in the surfactant concentration on k_obs. The kinetic effect of added NaClO₄ on the reaction rate in SB3‐14 micellar solutions has also been studied. They were rationalized by considering the binding of the perchlorate anions to the sulfobetaine micelles and their competition with the reactive bromide ions for the micellar surface. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 388–394, 2000     

Simultaneous Optimization of Surfactant Concentration and Organic Modifier in Micellar Liquid Chromatography. Application to the Separation of Phenolic Compounds

ABSTRACT

The separation selectivity of eighteen phenolic derivatives in micellar high-performance liquid chromatography was studied as a function of parameters on which it depends: surfactant and organic modifier concentration. The surfactant used in this study was cetyltrimethylammonium bromide, and as organic modifier methanol. An iterative regression optimization strategy for these two parameters has been used. The equation that best explains the experimental

results is 1/k' = A +Bμ + Cφ + DμΦ. We propose the use of this model in conjunction with the appropriate factorial design to predict the solute retention behaviour in micellar liquid chromatography with hibrid eluents.     

Dispersive liquid–liquid microextraction based on the solidification of deep eutectic solvent for the determination of benzoylureas in environmental water samples

We present a novel dispersive liquid–liquid microextraction method based on the solidification of deep eutectic solvent coupled with high‐performance liquid chromatography with a variable‐wavelength detection for the detection of five benzoylureas in real water samples. In this work, a green solvent consisting of 1‐octyl‐3‐methylimidazolium chloride and 1‐dodecanol was used as an extraction solvent, yielding the advantages of material stability, low density, and a suitable freezing point near room temperature. Parameters that significantly affect extraction efficiency were optimized by the one‐factor‐at‐a‐time approach. Under optimal conditions, the recoveries of five target compounds were obtained ranging from 87.39 to 98.05% with correlation coefficients ranging from 0.9994 to 0.9997 for pure water. The limits of detection were in the range of 0.09–0.16 μg/L. The enrichment factors were in the range of 171–188. Linearities were achieved in the range of 0.5–500 μg/L. The proposed method was successfully applied to determine benzoylureas in environmental water samples with a satisfactory recovery of approximately 81.38–97.67%.     

Two-dimensional fluorescence correlation spectroscopy II: spectral analysis of derivatives of anthracene and pyrene in micellar solutions

Generalized two-dimensional (2D) correlation spectroscopy has been applied to the analysis of fluorescence spectra in two micellar systems: (1) a mixture of pyrene and 1,3,6,8-pyrenetetrasulfonic acid in the cationic micellar solutions of cetyltrimethylammonium chloride (CTAC) and (2) a mixture of pyrene and 9-anthracencepropionic acid in anionic micellar solutions of sodium dodecyl sulfate (SDS). Fluorescence quenching is employed as a perturbation mode for causing intensity changes in fluorescence bands (quenching perturbation). Iodide ion (I-) is used as a quencher in the former system, and cetyl pridinium chloride (CPC) is used in the latter. Vibronic bands in the complicated fluorescence spectra of the mixture of the analytes were successfully resolved. It is shown that asynchronous maps are especially useful for spectral resolution enhancement when the quenching perturbation is employed in 2D fluorescence correlation spectroscopy. Furthermore, the information about the order of response of the bands to quenching is obtained by comparing the signs of synchronous and asynchronous cross-peaks.     

Investigation of the chiral surfactant N-dodecoxycarbonylvaline in electrokinetic chromatography: improvements in elution range and pH stability via mixed micelles and vesicles, and the hydrophobicity determination of basic pharmaceutical drugs

The chiral surfactant dodecoxycarbonylvaline (DDCV) has proven to be an effective pseudostationary phase for the separation of many enantiomeric pharmaceutical compounds. In this study the elution range and the prediction of octanol-water partitioning for the DDCV micellar system was examined. Through incorporation of DDCV in mixed micelles and unilamellar vesicles, enhancement of the elution range was observed. The mixed micelles contained a second anionic surfactant, sodium dodecyl sulfate (SDS), while the vesicles were composed of DDCV and the cationic surfactant cetyltrimethylammonium bromide (CTAB). Enantioselectivity, as well as other chromatographic and electrophoretic parameters, were compared between the mixed micelles, vesicles, and DDCV micelles. The hydrophobicity of the DDCV system was also evaluated as a predictor of n-octanol-water partition coefficients for 15 beta amino alcohols. The correlation between the logarithm of the retention factor (log k) and log P(ow) for seven hydrophobic beta-blockers and eight beta-agonists were r2 = 0.964 and r2 = 0.814, respectively.     

Determination of cationic surfactants in soil samples by the disulphine blue active substance (DBAS) procedure

A method for the determination of cationic surfactants in soil samples was developed and applied to a biodegradation study. Five different cationic surfactants (benzalkonium chloride, 1-dodecyl-3-methylimidazolium bromide, didecyldimethylammonium bromide, trihexyl(tetradecyl)phosphonium bromide and trihexyl(tetradecyl)phosphonium chloride) were selected for the study with the developed method upon extraction from soil samples with methanol. The samples were subjected to analysis as disulphine blue active substances using a visible spectrophotometer. The limits of detection for the proposed method ranged from 2 to 27 μg/g, which enabled the determination of cationic surfactants in soil samples. The results obtained in the biodegradation study were confirmed using liquid chromatography coupled with tandem mass spectrometry.     

胶束对酸碱指示剂离解平衡和变色点及变色范围的影响

探讨了十六烷基三甲基溴化铵(CTMAB),十二烷基硫酸钠(SDS)和TritonX-1003种胶束对酸套指示剂百里香酚蓝和溴百里香酚蓝离解反庆的离解常数的影响,进行了研究了以上3种胶束对指示剂变色点的变以范围的影响,实验结果表明,选择适当的胶束溶液作为滴定介质,不仅可以扩大酸碱指示剂的应用范围,而且还大大提高了测量的准确度.     

Nitrite Ionic Liquids (IL‐ONO and [bmim]NO2) as Effective Nitrosonium Sources for the Synthesis of α‐Oximinoketones under Mild Heterogeneous Conditions

Ketones and β‐diketones were nitrosated and converted to their corresponding α‐oximinoketones using task‐specific ionic liquids, 1‐(4‐nitritobutyl)‐3‐methylimidazolium chloride, IL‐ONO, and 1‐butyl‐3‐methylimidazolium nitrite at room temperature. The results from two ionic liquids are comparable and showed that these IL's are effective nitrosonium sources for the preparation of oximinoketones. The protocol is rapid, the yields are excellent, and the method is simple.     

Ionic‐liquid‐functionalized zinc oxide nanoparticles for the solid‐phase extraction of triazine herbicides in corn prior to high‐performance liquid chromatography analysis

Zinc oxide nanoparticles have recently been used as effective adsorbent materials for sample pretreatment in analytical chemistry because of their excellent properties, such as high specific surface area, high effective porosity, non‐toxicity, and ease of fabrication. In this study, the zinc oxide nanoparticles functionalized by an ionic liquid, 1‐carboxyethyl‐3‐methylimidazolium chloride, were fabricated and used as the adsorbent for the solid phase extraction of five triazine herbicides in corn for the first time. High‐performance liquid chromatography was employed for the determination of these triazine herbicides. Several experimental parameters affecting the extraction efficiency were investigated, including the volume of extraction solvent, the extraction time, the type of extraction solvent and elution solvent, the amount of absorbent, and the volume of elution solvent. By using the proposed method, low limits of detection and quantification for all the five triazine herbicides were obtained between 0.71–1.08 and 2.67–3.64 ng/g, respectively. Recoveries of the proposed method range from 89.05 to 100.33% with intra‐ and inter‐day relative standard deviations lower than 8.45%. The calibration curves are linear in the concentration range of 0.005–1.00 μg/g with the correlation coefficient higher than 0.9954.