The potential of the use of deep eutectic solvents and amino acid-based ionic liquids to enhance the chiral discrimination ability of different chiral selectors in capillary electrophoresis

The effect of the combined use of amino acid-based ionic liquids (AAILs) and deep eutectic solvents (DESs) with either cyclodextrin- (CD) or cyclofructan- (CF) based chiral selectors for the chiral separation of amphetamine derivatives was investigated in the present study. A non-significant improvement in enantiomeric separation of target analytes was observed when AAILs were combined with either CF or CD. On the other side, a markedly improved chiral separation of enantiomers was obtained using the dual carboxymethyl-β-cyclodextrin/DES system, highlighting the existence of a synergistic effect. After the addition of 0.5% v/v of choline chloride-ethylene glycol, the resolution of the enantiomers of amphetamine, methamphetamine and 3-fluorethamphetamine, increased from 1.4, 1.1, 1.0 to 1.8, 1.8, and 1.5 min, and the analysis times increased from 19.54, 20.48, 18.71 to 35.71, 35.78 and 32.90 min, respectively. This was not the case for the CF/DES dual system, in which the separation of amphetamines worsened, indicating an antagonistic effect. In conclusion, DESs are a very promising additive in capillary electrophoresis that can improve the separation of chiral molecules in combination with CDs but not CFs.

Green synthesis of monolithic column incorporated with graphene oxide using room temperature ionic liquid and eutectic solvents for capillary electrochromatography

In this work, a hybrid monolith incorporated with graphene oxide (GO) was prepared in the first time with binary green porogens of deep eutectic solvents (DESs) and room temperature ionic liquids (RTILs). GO was modified with 3-(trimethoxysilyl) propylmethacrylate (γ-MPS), and the resultant GO-MPS can be incorporated into poly (methacrylic acid-co-butylmethacrylate-co-ethylene glycol dimethacrylate) monoliths covalently. A hybrid monolithic column with high permeability and homogeneity can be achieved due to good dispersion of GO-MPS in the green solvents. The GO-MPS incorporated monolith was characterized by transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis and nitrogen adsorption tests. The separation of small organic molecules of alkylphenones and alkylbenzenes was used to evaluate the performance of GO-MPS grafted monolith. The GO-MPS grafted monolith displayed the maximum column efficiency of 147,000 plates/m, about twice higher than the GO-free monolith. In addition, all of the retention and selectivity of small molecules of alkylphenones and alkylbenzenes increased due to the addition of GO-MPS. The results demonstrated that the use of DESs and RTILs is a powerful approach for the preparation of GO incorporated polymer monoliths. The monolith was further applied to the separation of tryptic digests from bovine serum albumin, and the result indicated its potential in the analysis of some complex samples.

Simultaneous extraction and HPLC determination of 3-indole butyric acid and 3-indole acetic acid in pea plant by using ionic liquid-modified silica as sorbent

In this study, ionic liquid-modified silica was used as sorbent for simultaneous extraction and preconcentration of 3-indole butyric acid and 3-indole acetic acid in pea plants. The effect of some parameters such as pH and ionic strength of sample solution, amount of sorbent, flow rate of aqueous sample solution and eluent solution, concentration of eluent solution, and temperature were studied for each hormone solution. Percent extraction of 3-indole butyric acid and 3-indole acetic acid was strongly affected by pH of aqueous sample solution. Ionic strength of aqueous phase and temperature showed no serious effects on extraction efficiency of studied plant hormones. Obtained breakthrough volume was 200mL for each of studied hormones. Preconcentration factor for spectroscopic and chromatographic determination of studied hormones was 100 and 4.0×10(3) respectively. Each solid sorbent phase was reusable for almost 10 times of extraction/stripping procedure. Relative standard deviations of extraction/stripping processes of 3-indole butyric acid and 3-indole acetic acid were 2.79% and 3.66% respectively. The calculated limit of detections for IBA and IAA were 9.1×10(-2)mgL(-1) and 1.6×10(-1)mgL(-1) respectively.

Separation of Berberine Hydrochloride and Tetrahydropalmatine and Their Quantitative Analysis with Thin Layer Chromatography Involved with Ionic Liquids

[BMIM]OH was used in mobile and stationary phase of thin layer chromatography (TLC) to analyze berberine hydrochloride and tetrahydropalmatine for the first time. Supported imidazole ionic liquid with hydroxide ion on silica gel (SiO2·Im(+)·OH(-)) was synthesized through simple procedure and characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis, and scanning electron microscope (SEM). Moreover, on the plates prepared by SiO2·Im(+)·OH(-), the contents of the above alkaloids in the Chinese patent medicine (CPM) of "Stomacheasy" capsule were successfully determined by TLC scanner. The key conditions and chromatographic behaviors were also investigated in detail. According to similar ways, ionic liquids (ILs) also can be used in other planar chromatographies in two modes. This study is expected to be helpful in expanding the application of IL and its bonded silica gel in TLC separation field.

Recent development of ionic liquid stationary phases for liquid chromatography

Based on their particular physicochemical characteristics, ionic liquids have been widely applied in many fields of analytical chemistry. Many types of ionic liquids were immobilized on a support like silica or monolith as stationary phases for liquid chromatography. Moreover, different approaches were developed to bond covalently ionic liquids onto the supporting materials. The obtained ionic liquid stationary phases show multi-mode mechanism including hydrophobic, hydrophilic, hydrogen bond, anion exchange, π-π, and dipole-dipole interactions. Therefore, they could be used in different chromatographic modes including ion-exchange, RPLC, NPLC and HILIC to separate various classes of compounds. This review mainly summarizes the immobilized patterns and types of ionic liquid stationary phases, their retention mechanisms and applications in the recent five years.

Capillary and microchip electrophoretic analysis of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants which can reach the environment and food in different ways. Because of their high toxicity, two international regulatory institutions, the US Environmental Protection Agency and the European Food Safety Authority, have classified PAHs as priority pollutants, generating an important demand for the detection and identification of PAHs. Thus, sensitive, fast, and cheap methods for the analysis of PAHs in environmental and food samples are urgently needed. Within this context, electrophoresis, in capillary or microchip format, displays attractive features. This review presents and critically discusses the published literature on the different approaches to capillary and microchip electrophoresis analysis of PAHs.

Study on an electrochromatography method based on organic-inorganic hybrid molecularly imprinted monolith for determination of trace trichlorfon in vegetables

BACKGROUND

Organophosphorus pesticides have been widely used in agricultural production. However, the wide use of organophosphate also results in pesticide residues on the plant, which are harmful to human health because of their potential mutagenic and carcinogenic properties. Therefore, it is vital to develop a sensitive and effective analysis method to control pesticide residues.

RESULTS

In this study, a novel molecularly imprinted capillary monolithic column was prepared using trichlorfon as the template molecule by combining non-hydrolytic sol-gel process with a molecular imprinting technique. The resulting material was characterized by scanning electron microscopy and Fourier transform infrared. Under capillary electrochromatography, the effects of voltage, pH, ACN content and concentration of buffer solution on the electro-osmotic flow (EOF) of imprinted capillary monolithic column were evaluated in detail. Using this prepared material as stationary phase for capillary electrochromatography, a novel method of molecularly imprinted capillary electrochromatography (MICEC) for the detection of trace trichlorfon residues in vegetables was developed. Under optimal conditions, appreciable sensitivity was achieved with a LOD (S/N = 3) of 92.5 µg kg(-1) and method quantitation limit (MQL) of 305.3 µg kg(-1), respectively. The linear ranges of the calibration graph were 0.1 µg L(-1) to 10 mg L(-1). The peak area precision (RSD) for five replicate extractions of 0.01 mg L(-1) trichlorfon standard aqueous solution was 4.5%. To evaluate the accuracy of this method, the blank cucumber and cauliflower samples spiked with trichlorfon were extracted and analyzed by this method with good recoveries, ranging from 80.2% to 95.8%. Moreover, this method was successfully applied to the quantitative detection of the trichlorfon residues in leek samples.

CONCLUSION

With good properties of high sensitivity and simple pre-treatment, this MICEC method could provide a new tool for the rapid determination of trace trichlorfon residue in complex food samples.

Recent advances of ionic liquids and polymeric ionic liquids in capillary electrophoresis and capillary electrochromatography

Ionic liquids (ILs) and polymeric ionic liquids (PILs) with unique and fascinating properties have drawn considerable interest for their use in separation science, especially in chromatographic techniques. In this article, significant contributions of ILs and PILs in the improvement of capillary electrophoresis and capillary electrochromatography are described, and a specific overview of the most relevant examples of their applications in the last five years is also given. Accordingly, some general conclusions and future perspectives in these areas are discussed.

Improvement of the chromatographic separation performance of an imidazolium ionic liquid functionalized silica column by in situ anion-exchange with dodecyl sulfonate and dodecylbenzene sulfonate anions

The anionic part of ionic liquids can provide additional interactions during chromatographic separations. In this work, the chromatographic separation performance of a silica column functionalized with 1-propyl-3-methylimidazolium chloride ionic liquid was improved by in situ anion-exchange from chloride anions to dodecyl sulfonate anions and dodecylbenzene sulfonate anions. The separation performances of these ionic liquid functionalized phases were investigated and compared with each other using polycyclic aromatic hydrocarbons, phthalates, parabens, and phenols as model compounds. Results indicated that the new columns presented a better chromatographic separation than the original one. This was ascribed retention mechanism from organic anions. The introduction of dodecyl sulfonate anions increased the hydrophobicity of stationary phase. Furthermore, the phenyl groups of dodecylbenzene sulfonate anions could provide an enhanced selectivity to aromatic compounds such as polycyclic aromatic hydrocarbons by π-π interactions. Analysis repeatability of the new columns was satisfactory (RSD of retention time, 0.10-0.40%; RSD of peak area, 0.66-0.84%).

Imidazolium-based ionic liquids grafted on solid surfaces

Supported ionic liquids (SILs), which refer to ionic liquids (ILs) immobilized on supports, are among the most important derivatives of ILs.

Dipyridyl-immobilized ionic liquid type hybrid silica monolith for hydrophilic interaction electrochromatography

A pyridinium-based immobilized ionic liquid type multifunctional hybrid silica monolith was prepared by the in situ polymerization of 3-chloropropyl-silica matrix and 4,4'-dipyridyl for hydrophilic interaction CEC. The obtained hybrid monolith possessed of high stable skeletal microstructures with obviously hydrophilic retention mechanism under ACN content >50% in the mobile phase. Strong and stable anodic EOF could be observed under a broad pH range from pH 3.0 to 9.0. Due to the immobilized dipyridyl groups bonded to the silica matrix surface, the resulting hydrophilic hybrid monolith possessed multiple separation interactions including hydrogen bond, π-π, and anion exchange. Excellent separations of various polar analytes including electroneutral phenols, charged acid nucleotides, and basic analytes were successfully achieved. The highest column efficiencies up to 120,000, 164,000, and 106,000 plates/m were obtained for nucleotides, nucleic acid bases, and nucleosides and nicotines, respectively. These results demonstrated that the dipyridyl-immobilized ionic liquid functionalized hybrid monolith possessed highly mechanical stability and good chromatographic performance for hydrophilic interaction electrochromatography.

Use of chiral amino acid ester-based ionic liquids as chiral selectors in CE

In this study, the applicability of a chiral ionic liquid (CIL) as the sole chiral selector in CE was investigated for the first time. In particular, five amino acid ester-based CILs were synthesized and used as additives in the BGE in order to evaluate their chiral recognition ability. The performance of these CILs as the sole chiral selectors was evaluated by using 1,1'-binaphthyl-2,2-diylhydrogenphosphate (BNP) as the analyte and by comparing the resolution values. Different parameters were examined, such as the alkyl group bulkiness and the configuration of the cation, the anion type of the CIL and its concentration, and the pH of the BGE, in order to optimize the separation of the enantiomers and to demonstrate the effect that each parameter has on the chiral-recognition ability of the CIL. Baseline separation of BNP within 13 min was achieved by using a BGE of 100 mM Tris/10 mM sodium tetraboratedecahydrate (pH 8) and a chiral selector of 60 mM l-alanine tert butyl ester lactate. The run-to-run and batch-to-batch reproducibilities were also evaluated by computing the %RSD values of the EOF and the two enantiomer peaks. In both cases, very good reproducibilities were observed, since all %RSD values were below 1%.

Cage-like silica nanoparticles-functionalized silica hybrid monolith for high performance capillary electrochromatography via "one-pot" process

A cage-like silica nanoparticles-functionalized silica hybrid monolith for high performance capillary electrochromatography (CEC) has been prepared via "one-pot" process. In this process, the polycondensation of hydrolyzed alkoxysilanes and in situ reaction of mercaptopropyltrimethoxysilane (MPTS) with sodium 3-mercapto-1-propanesulfonate modified octavinyloctasilasesquioxane (MPS-OVS) simultaneously occurred in a pretreated capillary. The characterization and evaluation results indicated that the obtained MPS-OVS hybrid monolithic capillary column has homogeneous macroporous morphology with a permeability of 5.37×10(-13)m(2) and strong electro osmotic flow (EOF) over a wide pH range from 2.7 to 11.2. The EOF on the MPS-OVS hybrid monolithic column reached its maximum of 0.327cm(2)kV(-1)s(-1) at pH 9.7. The best theoretical efficiency of ∼470,000plates/m was obtained for 2-aminophenol in CEC. Anilines and phenols were well separated on the MPS-OVS hybrid monolithic column by CEC, indicating typical reversed-phase and cation-exchange chromatographic retention mechanisms of the column. The monolith was further applied to the separation of bovine serum albumin (BSA) tryptic digests, and the result indicated its potential in the analysis of some complex samples.

Recent advances in preparation and application of hybrid organic-silica monolithic capillary columns

Hybrid organic-silica monolithic columns, regarded as a second generation of silica-based monoliths, have received much interest due to their unique properties over the pure silica-based monoliths. This review mainly focuses on development in the fields of preparation of hybrid monolithic columns in a capillary and their application for CEC and capillary liquid chromatography separation, as well as for sample pretreatment of solid-phase microextraction and immobilized enzyme reactor since July 2010. The preparation approaches are comprehensively summarized with three routes: (i) general sol-gel process using trialkoxysilanes and tetraalkoxysilanes as coprecursors; (ii) "one-pot" process of alkoxysilanes and organic monomers concomitantly proceeding sol-gel chemistry and free radical polymerization; and (iii) other polymerization approaches of organic monomers containing silanes. The modification of hybrid monoliths containing reactive groups to acquire the desired surface functionality is also described.

Phosphonium-based ionic liquids in electrokinetic capillary chromatography for the separation of neutral analytes

In this work we elucidated the applicability of phosphonium-based ionic liquids (ILs) as pseudostationary phase in electrokinetic capillary chromatography (EKC) with UV-detection. The phosphonium ILs studied contain bromide, chlorine, or tosylate ions, as counter ions, and alkyl side chains of variable length on the phosphorous atom. The effects of the type and concentration of the IL, pH, ionic strength, and type of background electrolyte solution on the electroosmotic flow (EOF) and on the effective electrophoretic mobilities of some neutral model analytes were investigated and large variations in the migration times were observed. Especially the IL employed remarkably affected the strength and direction of the EOF Successful separations were obtained for neutral aromatic singly substituted analytes, namely benzene, toluene, phenol, and nitrobenzene. The results demonstrated the potential of capillary electromigration methods for rapid interaction studies between ILs and analytes, which is useful for the development of novel materials for sample preparation and separation purposes or for novel catalyst and chemical processing studies.

Ionic liquid-modified materials for solid-phase extraction and separation: a review

In recent years, materials science has propelled to the research forefront. Ionic liquids with unique and fascinating properties have also left their footprints to the developments of materials science during the last years. In this review we highlight some of their recent advances and provide an overview at the current status of ionic liquid-modified materials applied in solid-phase extraction, liquid and gas chromatography and capillary electrochromatography with reference to recent applications. In addition, the potential of ionic liquids in the modification of capillary inner wall in capillary electrophoresis is demonstrated. The main target material modified with ionic liquids is silica, but polymers and monoliths have recently joined the studies. Although imidazolium is still clearly the most commonly used ionic liquid for the covalently modification of materials, the exploitation of pyridinium and phosphonium will most probably increase in the future.