Extraction of organic compounds with room temperature ionic liquids

Room temperature ionic liquids are novel solvents with a rather specific blend of physical and solution properties that makes them of interest for applications in separation science. They are good solvents for a wide range of compounds in which they behave as polar solvents. Their physical properties of note that distinguish them from conventional organic solvents are a negligible vapor pressure, high thermal stability, and relatively high viscosity. They can form biphasic systems with water or low polarity organic solvents and gases suitable for use in liquid–liquid and gas–liquid partition systems. An analysis of partition coefficients for varied compounds in these systems allows characterization of solvent selectivity using the solvation parameter model, which together with spectroscopic studies of solvent effects on probe substances, results in a detailed picture of solvent behavior. These studies indicate that the solution properties of ionic liquids are similar to those of polar organic solvents. Practical applications of ionic liquids in sample preparation include extractive distillation, aqueous biphasic systems, liquid–liquid extraction, liquid-phase microextraction, supported liquid membrane extraction, matrix solvents for headspace analysis, and micellar extraction. The specific advantages and limitations of ionic liquids in these studies is discussed with a view to defining future uses and the need not to neglect the identification of new room temperature ionic liquids with physical and solution properties tailored to the needs of specific sample preparation techniques. The defining feature of the special nature of ionic liquids is not their solution or physical properties viewed separately but their unique combinations when taken together compared with traditional organic solvents.     

Determination of atranol and chloroatranol in perfumes using simultaneous derivatization and dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

A new analytical method based on simultaneous derivatization and dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography–mass spectrometry (GC–MS), for the determination of the allergenic compounds atranol and chloroatranol in perfumes, is presented. Derivatization of the target analytes by means of acetylation with anhydride acetic in carbonate buffer was carried out. Thereby volatility and detectability were increased for improved GC–MS sensitivity. In addition, extractability by DLLME was also enhanced due to a less polar character of the solutes. A liquid–liquid extraction was performed before DLLME to clean up the sample and to obtain an aqueous sample solution, free of the low polar matrix from the essential oils, as donor phase. Different parameters, such as the nature and volume of both the extraction and disperser solvents, the ionic strength of the aqueous donor phase or the effect of the derivatization reagent volume, were optimized. Under the selected conditions (injection of a mixture of 750 μL of acetone as disperser solvent, 100 μL of chloroform as extraction solvent and 100 μL of anhydride acetic as derivatization reagent) the figures of merit of the proposed method were evaluated. Limits of detection in the low ng mL⁻¹ range were obtained. Matrix effect was observed in real perfume samples and thus, standard addition calibration is recommended.     

Ionic Liquids-New "Solutions" for Transition Metal Catalysis

Ionic liquids are salts that are liquid at low temperature (<100 degrees C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.     

Multi-residue quantification of veterinary drugs in milk with a novel extraction and cleanup technique: Salting out supported liquid extraction (SOSLE)

A quantitative liquid chromatography coupled with high-resolution mass spectrometry method was developed for the determination of more than one hundred compounds belonging to a variety of veterinary drug classes in bovine milk. Salting out supported liquid extraction (SOSLE), a novel extraction and cleanup technique, was introduced to ensure high extraction efficiency and good sample cleanup. The high salt (ammonium sulfate) concentration in the aqueous donor phase permits supported liquid/liquid extraction (SLE) with a relative polar organic acceptor phase (acetonitrile). This is different from traditional SLE, in which the need for phase separation results in the selection of organic solvents with intermediate polarities (e.g., ethyl acetate or dichloromethane). Hence, SOSLE is more efficient in recovering polar analytes than conventional SLE. SOSLE was also compared to classical approaches like solid phase extraction, QuEChERS and ultra-filtration. The proposed technique resulted in extracts of equal or superior cleanliness and with higher average recoveries than those obtained with QuEChERS or SPE. The recovery (median for all compounds) was 73% for QuEChERS, 83% for SPE and 91% for SOSLE. The most significant improvements were observed for polar analytes (penicillines, quinolones and tetracyclines) which are hardly recovered by QuEChERS. The chromatographic separation and detection was based on an ultra-high-performance liquid chromatography Q-Orbitrap system (Q-Exactive plus). The developed analytical method has been validated (based on the commission decision 2002/957/EC) as required for quantitative veterinary drug methods.     

Etude physico-chimique de la solubilite de la polyvinylpyrrolidone et d'autres polybases de lewis,dans des melanges binaires de solvants polaires

We have measured the solubility of polyvinylpyrrolidone and some other polar polymers in organic mixtures composed of halogenated solvents and proton donors such as alcohols or carboxylic acids. As a general rule, a coacervation zone appears which is limited by a closed curve. This property is explained by a selective adsorption of the donor compound by the polymer, leading to a macromolecular complex via hydrogen bonds. This phenomenon is particularly marked when both solvents are near demixing conditions.     

The influence of organic sample solvents on the separation efficiency of basic compounds under strong cation exchange mode

This study investigated the influence of organic sample solvents on separation efficiency of basic compounds under strong cation exchange (SCX) mode. The mixtures of acidic aqueous solution and organic solvent such as acetonitrile, ethanol, methanol and dimethyl sulfoxide (DMSO) were tested as sample solvents. For later-eluting analytes, the increase of sample solvent elution strength was responsible for the decrease of separation efficiency. Thus, sample solvents with weak elution strength could provide high separation efficiencies. For earlier-eluting analytes, the retention of organic sample solvents was the main factor affecting separation efficiency. Weakly retained solvents could provide high separation efficiency. In addition, an optimized approach was proposed to reduce the effect of organic sample solvent, in which low ionic solvent was employed as initial mobile phase in the gradient. At last, the analysis of impurities in hydrophobic drug berberine was performed. The results showed that using acidic aqueous methanol as sample solvents could provide high separation efficiency and good resolution (R > 1.5).     

Functional amino acid ionic liquids as solvent and selector in chiral extraction

Amino acid ionic liquids (AAILs) have received great attention due to their potentials in catalysis and separations. In this work, functional AAILs were used as solvent and selector in chiral liquid–liquid extraction for the first time. The AAILs have shown distinct enantioselectivity in amino acid extraction. Using these functional AAILs as acceptor phase and ethylacetate as donor phase, more L-enantiomer of amino acid was extracted into the ionic liquid phase than that of D-enantiomer. The influencing factors, including AAILs structure, copper ion concentration, organic phase and amino acid concentration, were investigated. We found that the enantioselective enrichment of racemic amino acids was achieved through a chiral ligand-exchange mechanism. The enantioselectivity of single-step extraction was up to enantiomeric excess value of 50.6%. Moreover, the functional AAILs were found to be efficient extraction solvents for amino acids. The logarithm of distribution coefficient for L-Phe was in the range of 3.4–3.6 in the ionic liquid–ethylacetate two-phase system. This liquid–liquid extraction approach may extend the application of ionic liquids in chiral separations.     

Ion chromatography with the indirect ultraviolet detection of alkali metal ions and ammonium using imidazolium ionic liquid as ultraviolet absorption reagent and eluent

Indirect ultraviolet detection was conducted in ultraviolet‐absorption‐agent‐added mobile phase to complete the detection of the absence of ultraviolet absorption functional group in analytes. Compared with precolumn derivatization or postcolumn derivatization, this method can be widely used, has the advantages of simple operation and good linear relationship. Chromatographic separation of Li⁺, Na⁺, K⁺, and NH₄⁺ was performed on a carboxylic acid base cation exchange column using imidazolium ionic liquid/acid/organic solvent as the mobile phase, in which imidazolium ionic liquids acted as ultraviolet absorption reagent and eluting agent. The retention behaviors of four kinds of cations are discussed, and the mechanism of separation and detection are described. The main factors influencing the separation and detection were the background ultraviolet absorption reagent and the concentration of hydrogen ion in the ion chromatography‐indirect ultraviolet detection. The successful separation and detection of Li⁺, Na⁺, K⁺, and NH₄⁺ within 13 min was achieved using the selected chromatographic conditions, and the detection limits (S/N = 3) were 0.02, 0.11, 0.30, and 0.06 mg/L, respectively. A new separation and analysis method of alkali metal ions and ammonium by ion chromatography with indirect ultraviolet detection method was developed, and the application range of ionic liquid was expanded.     

Application of 1-alkyl-3-methylimidazolium-based ionic liquids in non-aqueous capillary electrophoresis

In many cases salts, which are liquid at room temperature show a better solubility in organic solvents, and can be used in nonaqueous capillary zone electrophoresis as ionic additives. In this study 1-alkyl-3-methylimidasolium-based ionic liquids were used as additives in separation media to assess the interactions between the analytes and the ionic additive present and to find an influence of the type and concentration of the ionic additive, also the nature of the nonaqueous medium employed. Different organic solvents (acetonitrile and methanol) contribute differently to the conversion of analytes into a charged form. Complexes with either an anionic or a cationic part of the ionic liquid additive were formed. This was the case for electrophoresis separation of Br?nsted acids and polyphenolic compounds.     

Ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction for the separation and determination of estrogens in water samples by high‐performance liquid chromatography with fluorescence detection

An ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction method was proposed for the extraction and concentration of 17‐α‐estradiol, 17‐β‐estradiol‐benzoate, and quinestrol in environmental water samples by high‐performance liquid chromatography with fluorescence detection. 1‐Hexyl‐3‐methylimidazolium tetrafluoroborate was applied as foaming agent in the foam flotation process and dispersive solvent in microextraction. The introduction of the ion‐pairing and salting‐out agent NH₄PF₆ was beneficial to the improvement of recoveries for the hydrophobic ionic liquid phase and analytes. Parameters of the proposed method including concentration of 1‐hexyl‐3‐methylimidazolium tetrafluoroborate, flow rate of carrier gas, floatation time, types and concentration of ionic liquids, salt concentration in samples, extraction time, and centrifugation time were evaluated. The recoveries were between 98 and 105% with relative standard deviations lower than 7% for lake water and well water samples. The isolation of the target compounds from the water was found to be efficient, and the enrichment factors ranged from 4445 to 4632. This developing method is free of volatile organic solvents compared with regular extraction. Based on the unique properties of ionic liquids, the application of foam floatation, and dispersive liquid–liquid microextraction was widened.     

Ionic liquids as surfactants in micellar liquid chromatography

This paper is devoted to application of ionic liquids as surfactants in LC of organic compounds, derivatives of 1,4‐thiosemicarbazides. According to HPLC requirements the most advantageous conditions such as transparency for ultraviolet light, low CMC, additional inorganic salt additives, and appropriate organic solvent were established. The CMC was determined using conductivity measurements. Suitability of two different stationary phases: RP‐C18 and cyanopropyl bonded phase was examined under micellar conditions. Chosen ionic liquid surfactant was compared to common traditional amphiphilic reagent – SDS. Elaborated on chromatographic micellar conditions were tested as a pilot technique for prediction of distribution coefficients of organic analytes in ionic liquid‐based aqueous two‐phase system.     

Matrix solid‐phase dispersion coupled with homogeneous ionic liquid microextraction for the determination of sulfonamides in animal tissues using high‐performance liquid chromatography

Matrix solid‐phase dispersion coupled with homogeneous ionic liquid microextraction was developed and applied to the extraction of some sulfonamides, including sulfamerazine, sulfamethazine, sulfathiazole, sulfachloropyridazine, sulfadoxine, sulfisoxazole, and sulfaphenazole, in animal tissues. High‐performance liquid chromatography was applied to the separation and determination of the target analytes. The solid sample was directly treated by matrix solid‐phase dispersion and the eluate obtained was treated by homogeneous ionic liquid microextraction. The ionic liquid was used as the extraction solvent in this method, which may result in the improvement of the recoveries of the target analytes. To avoid using organic solvent and reduce environmental pollution, water was used as the elution solvent of matrix solid‐phase dispersion. The effects of the experimental parameters on recoveries, including the type and volume of ionic liquid, type of dispersant, ratio of sample to dispersant, pH value of elution solvent, volume of elution solvent, amount of salt in eluate, amount of ion‐pairing agent (NH₄PF₆), and centrifuging time, were evaluated. When the present method was applied to the analysis of animal tissues, the recoveries of the analytes ranged from 85.4 to 118.0%, and the relative standard deviations were lower than 9.30%. The detection limits for the analytes were 4.3–13.4 μg/kg.     

Novel zwitterionic polyphosphorylcholine monolithic column for hydrophilic interaction chromatography

A novel porous zwitterionic monolith was prepared by thermal co-polymerisation of 2-methacryloyloxyethyl phosphorylcholine (MPC) and ethylene glycol dimethacrylate (EDMA) within 100 μm I.D. capillaries. Mercury intrusion porosimetry, scanning electron microscopy (SEM), micro-HPLC (μ-HPLC), elemental analysis and ζ-potential analysis were used to evaluate the monolithic structure. No evidence of swelling or shrinking of the monolith in different polarity solvents was observed. A typical hydrophilic liquid chromatography (HILIC) mechanism was observed at high organic solvent content (acetonitrile >60%). The phosphorylcholine (PC) functionality has both a positively charged quaternary ammonium and a negatively charged phosphate group. For charged analytes, a weak electrostatic interaction was also observed by studying the influence of mobile phase pH and salt concentration on their retentions on the poly(MPC-co-EDMA) monolithic column. The optimised poly(MPC-co-EDMA) monolith showed very good selectivities for a range of polar test analytes, especially small peptides. This might be ascribed to the good biocompatibility of PC functionality. At low organic solvent content, baseline separation was also observed for a test mixture of seven alkylphenones by a reversed-phase separation mechanism.     

大气颗粒物滤膜中极性有机物在线衍生装置的设计与应用

设计制作了一套用于气相色谱-质谱(GC-MS)分析极性有机物的在线衍生装置,并将其应用于大气颗粒物样品中极性有机物的检测.将大气颗粒物滤膜样品置于GC-MS进样口,通过使用套针组件,匀速引入气态衍生试剂N-甲基-Ⅳ-(三甲基硅烷)三氟乙酰胺(MSTFA),使其在衬管内于310℃下与待测物接触,10 min即可完成硅烷化...     

Ionic liquid‐bonded polysiloxane as stationary phase for capillary gas chromatography

Ionic liquid (IL) stationary phase is especially suitable for separation of complex samples, owing to the “dual nature” of IL. In this study, a synthetic method of ionic liquid‐bonded polysiloxane (PSOIL) as stationary phase of GC was proposed. Then, the PSOIL was used to prepare an 8 m capillary column by static method. The column efficiency was measured to be about 4000 plates/m (k=3.55, naphthalene) after the column had been conditioned at 210°C. The durability of PSOIL column was better than that of the mixed stationary phase of IL and OV‐1. Moreover, the Abraham solvation parameter model was employed to characterize the PSOIL. The result revealed that the PSOIL had stronger dispersion force (l) than neat IL and stronger hydrogen bond basicity (a) than DB‐1. That meant the PSOIL might offer good selectivity for both polar and non‐polar analytes. The column exhibited unique selectivity for various organic substances, such as the homologous compounds of alkanes, esters, alcohols and aromatic compounds. It was also found that some aromatic positional isomers could be separated better on the PSOIL column than on the DB‐1 column. Furthermore, the stationary phase was suitable for separation of high‐boiling point compounds such as polycyclic aromatic hydrocarbons, phthalic esters, etc. All of these demonstrated that the PSOIL offered good selectivity and high separation efficiency for a wide range of analytes.     

High-performance liquid chromatographic separation of bilirubin conjugates: the effects of change in molarity and pH

A fast, sensitive high-performance liquid chromatographic method has been developed for the separation and quantitation of biliary bile pigments; this utilizes a C18 reversed-phase column with two solvents, a buffer and an organic solvent, which were changed in a linear gradient from a polar to a less polar combination. Nine glycosidic conjugates of bilirubin as well as unconjugated bilirubin and a suitable internal standard, unconjugated mesobilirubin IX alpha, were all separated to baseline by gradient elution; the species eluted in a polar to less polar fashion. Increasing the molarity of the solvent decreased the binding of non-glucuronide pigments to the column, with a decrease in their retention times, whereas for bilirubin monoglucuronide they increased. Decrease in pH, similarly, preferentially increased bilirubin monoglucuronide retention times.     

A computational study of ion speciation in mixtures of protic ionic liquids with various molecular solvents: Insight into the solvent polarity and anion basicity

The ion pairing state of the ionic liquids greatly depends on the cosolvent which subsequently affects the properties and the functionalities. Density functional calculations have been performed to study the ion pairing formation process of protic ionic liquids (PILs) ([Et₃NH][CH₃SO₃]/TEAMS or [Et₃NH][CF₃SO₃]/TEATF) dissolved in different solvents. The clusters involving the cation, anion, and different number of solvent molecules have been used to simulate the contact ion pairs (CIPs) and the solvent‐separated ion pairs (SIPs) in the mixtures with varying solvent concentrations. The geometric, energetic data, and the natural bond orbital analysis suggest the smallest number of the water molecules required to break the TEAMS CIPs is four, while it is three for TEATF. This is consistent with the experimental prediction that if the mixture of TEAMS and water was replaced by TEATF and water, the transition process began at a lower water concentration. Furthermore, the calculated results also confirm that the weakly polar organic solvents favor the CIP form at all solvent concentrations, while the high polarity solvents promote dissociation of the CIP to generate the SIP form for particular PILs. The different separation nature of the given solvents can be interpreted in terms of their distinct hydrogen bond donor and acceptor abilities.     

Determination of Four Pesticides in Soil by Homogeneous Ionic Liquid-based Microextraction Coupled with High-performance Liquid Chromatography

Homogeneous ionic liquid microextraction was developed for the simultaneceus extraction of dimethomorph, mefenacet, isoprothiolane and oxadiazon from soil. 1-Butyl-3-methylimidazolium tetrafluoroborate was used as extraction solvent, and ammonium hexafluorophosphate was used as ion-pairing agent. High-performance liquid chromatography(HPLC) was employed for separation and determination of the analytes. The calibration curves show good linear relationship(r>0.9988). The recoveries are between 74.2% and 97.9% with relative standard deviations(RSDs) lower than 5.97%. The present method is free of volatile organic solvents, and expenditures of sample, extraction time and solvent are lower, compared with ultrasonic and Soxhlet extraction. There was no obvious diffe- rence in the extraction recoveries of pesticides obtained by the three extraction methods.     

Ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction and derivatization of sulfonamides in river water, honey, milk, and animal plasma

The ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction (IL-based MADLLME) and derivatization was applied for the pretreatment of six sulfonamides (SAs) prior to the determination by high-performance liquid chromatography (HPLC). By adding methanol (disperser), fluorescamine solution (derivatization reagent) and ionic liquid (extraction solvent) into sample, extraction, derivatization, and preconcentration were continuously performed. Several experimental parameters, such as the type and volume of extraction solvent, the type and volume of disperser, amount of derivatization reagent, microwave power, microwave irradiation time, pH of sample solution, and ionic strength were investigated and optimized. When the microwave power was 240 W, the analytes could be derivatized and extracted simultaneously within 90 s. The proposed method was applied to the analysis of river water, honey, milk, and pig plasma samples, and the recoveries of analytes obtained were in the range of 95.0-110.8, 95.4-106.3, 95.0-108.3, and 95.7-107.7, respectively. The relative standard deviations varied between 1.5% and 7.3% (n=5). The results showed that the proposed method was a rapid, convenient and feasible method for the determination of SAs in liquid samples.     

Impact of column temperature and mobile phase components on selectivity of hydrophilic interaction chromatography (HILIC)

The retention mechanism and chromatographic behavior for different polar analytes under hydrophilic interaction chromatography (HILIC) conditions have been studied by application of different mobile phases and stationary phases to various analytes at different temperatures. In addition to the commonly accepted mechanism of analyte liquid-liquid partitioning between mobile phase and water-enriched solvent layer which is partially immobilized onto the surface of the stationary phase, hydrogen-bonding, hydrophobic interaction, and ion-exchange interactions may also be involved. The predominant retention mechanism in HILIC separation is not always easily predictable. It can depend not only on the characteristics of the analytes but also on the selection of mobile and stationary phase compositions. The objective of this review is to evaluate the potential application of column temperature and mobile phase composition toward improving HILIC selectivity. The functional groups from analyte structures, stationary phase materials and organic mobile phase solvents will be highlighted.