Acetonitrile Ethyl Acetate Research Articles

Dynamic ultrasonic-assisted extraction coupled with paralleled counter-current chromatography for continuous extraction and online isolation of xanthenones from Garcinia mangostana

The automation of dynamic ultrasonic-assisted extraction (DUAE) coupled with paralleled counter-current chromatography (PCCC) was developed and used in the continuous extraction and online isolation of chemical constituents from Garcinia mangostana. The two-phase solvent system was prepared using automated equipment. The target compounds were extracted continuously by DUAE; after extraction, the extracted solution was pumped into a flash chromatographic column (FCC) for enrichment and purification. After enrichment and purification, the sample was eluted with the upper organic phase of the two-phase solvent system; the eluted solution was pumped into the CCC 1 column, and then the target compounds were eluted with the lower aqueous phase of the two-phase solvent system. During the CCC separation, the sample was continuously enriched and purified by the FCC, and the ten-port valve was switched to connect ports 1 and 2, followed by elution with the upper organic phase of the two-phase solvent system. The eluted solution was pumped into the CCC 2 column, and then the target compounds were eluted with the lower aqueous phase of the two-phase solvent system. When the first cycle of DUAE/PCCC was complete, the second cycle was performed. Five target compounds, i.e., 3-isomangostin, 8-desoxygartanin, mangostanol, gartanin, and α-mangostin, with purities above 94.28%, were successfully extracted and isolated online via a two-phase solvent system consisting of n-hexane–ethyl acetate–acetonitrile–methanol–water (5:2:5:1:3, v:v:v:v:v). This instrumental setup achieved systematic extraction and isolation of natural products, and has great prospects for industrial applications.

Investigation of the Composition for a Ternary Solvent System in Tube Radial Distribution Chromatography

A tube radial distribution chromatography (TRDC) system was developed based on the tube radial distribution of a ternary solvent system. The composition for the water–hydrophilic organic solvent–hydrophobic organic solvent in TRDC was investigated using phase diagrams, chromatograms, and fluorescence photographs. Mixtures of a hydrophilic organic solvent (acetonitrile, ethanol, methanol, 1-propanol, or 1,4-dioxane) and a hydrophobic solvent (ethyl acetate, hexane, 1-butanol, or chloroform) were examined as the ternary solvent system, which was the carrier solution in TRDC. Water–acetonitrile–chloroform and water–acetonitrile–ethyl acetate systems performed well in TRDC. A model analyte solution of 1-naphthol (NA) and 2,6-naphthalenedisulfonic acid was separated by TRDC using the chloroform solvent system with a range of volume ratios for the solvent components. The elution order of these two compounds could be reversed by changing the solvent system from organic solvent rich to water rich. A mixture of five analytes, NA, Eosin Y, 1-naphthalenesulfonic acid, 2,6-naphthalenedisulfonic acid, and 1,3,6-naphthalenetrisulfonic acid, was also separated using the water–acetonitrile–chloroform solvent system (32:65:3 volume ratio). These compounds eluted in the order given above.

Analysis of 1,2-diol diesters in vernix caseosa by high-performance liquid chromatography – atmospheric pressure chemical ionization mass spectrometry

Fatty acid diesters of long-chain 1,2-diols (1,2-DDE), or type II wax diesters, were analyzed in the vernix caseosa of a newborn girl. 1,2-DDE were isolated from the total lipid extract by the semipreparative TLC using plates coated with silica gel. Chromatographic separation of the 1,2-DDE molecular species was achieved on the non-aqueous reversed-phase HPLC with two Nova-Pak C18 columns connected in series (a total length of 45cm) and using an acetonitrile–ethyl acetate gradient. 1,2-DDE eluted from the column in the order of their equivalent chain number. The analytes were detected as ammonium adducts by an ion-trap mass spectrometer equipped with an atmospheric pressure chemical ionization source. Their structures were elucidated using tandem mass spectrometry with MS, MS2 and MS3 steps in a data-dependent mode. More than two thousand molecular species of 1,2-DDE were identified in 141 chromatographic peaks. The most abundant 1,2-DDE were monounsaturated lipids consisting of a C22 diol and a C18:1 fatty acid together with C16:0, C14:0 or C15:0 fatty acids. The positions of double bonds were characterized by the fragmentation of [M+C3H5N]+ formed in the ion source.

Investigating the role of solvent-solute interaction in crystal nucleation of salicylic acid from organic solvents.

In previous work, it has been shown that the crystal nucleation of salicylic acid (SA) in different solvents becomes increasingly more difficult in the order: chloroform, ethyl acetate acetonitrile, acetone, methanol, and acetic acid. In the present work, vibration spectroscopy, calorimetric measurements, and density functional theory (DFT) calculations are used to reveal the underlying molecular mechanisms. Raman and infrared spectra suggest that SA exists predominately as dimers in chloroform, but in the other five solvents there is no clear evidence of dimerization. In all solvents, the shift in the SA carbonyl peak reflecting the strength in the solvent-solute interaction is quite well correlated to the nucleation ranking. This shift is corroborated by DFT calculated energies of binding one solvent molecule to the carboxyl group of SA. An even better correlation of the influence of the solvent on the nucleation is provided by DFT calculated energy of binding the complete first solvation shell to the SA molecule. These solvation shell binding energies are corroborated by the enthalpy of solvent-solute interaction as estimated from experimentally determined enthalpy of solution and calculated enthalpy of cavity formation using the scaled particle theory. The different methods reveal a consistent picture and suggest that the stronger the solvent binds to the SA molecule in solution, the slower the nucleation becomes.

Study of complex formation process between 4′-nitrobenzo-18-crown-6 and yttrium(III) cation in some binary mixed non-aqueous solvents using the conductometry method

The complexation reaction between Y3+ cation and macrocyclic ligand, 4′-nitrobenzo-18-crown-6 (4′NB18C6), was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–1,2-dichloroethane (AN–DCE), acetonitrile–dimethylformamide (AN–DMF) and acetonitrile–ethylacetate (AN–EtOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most cases, the stoichiometry of the complex formed between 4′NB18C6 and Y3+ cation is 1:1 [M:L], but in the case of AN-DCE binary solution (mol% DCE=50) at 15, 25 and 35°C, a 2:1 [M2:L] and also a 2:2 [M2:L2] complexes are formed in solution. The results show that the stoichiometry of the complex formed between 4′NB18C6 and Y3+ cation changes with the composition of the mixed solvents and even with temperature. The stability constant of the 1:1 complex was determined using a computer program, GENPLOT. The stability order of (4′NB18C6.Y)3+ complex in pure studied solvents at 25°C was found to be: EtOAc>AN>MeOH>DMF and in the case of the mixed solvent solutions with 25mol percent of AN at 25°C was: AN-DCE>AN-EtOAc>AN-MeOH∼AN-DMF. The values of stability constant (logKf) of (4′NB18C6.Y)3+ complex which were obtained from conductometric data, show that the stability of the complex is not only affected by the nature and composition of the solvent system, but it is also influenced by the temperature. In all cases, a non-linear behavior is observed for changes of logKf of the (4′NB18C6.Y)3+ complex versus the composition of the binary mixed solvents. The values of standard thermodynamic quantities (ΔH°c and ΔS°c) for the complexation process which were obtained from temperature dependence of the stability constant of (4′NB18C6.Y)3+ complex, show that depending on the solvent system, in most cases, the complex is enthalpy and also entropy stabilized, but in some cases, it is stabilized or destabilized from these view points.

Capillary Chromatography Using an Annular and Sluggish Flow in the Ternary Water–Acetonitrile–Ethyl Acetate System as Carrier Solution

Abstract An open-tubular capillary chromatography system was developed using an annular and sluggish flow system in a ternary water–acetonitrile–ethyl acetate mixed solvent as carrier solution. Fused-silica capillary tubes with different inner diameters of 75 and 200 µm were used. The smaller tube was inserted into the larger tube using a T-type joint. Water–acetonitrile and acetonitrile–ethyl acetate mixed solutions were delivered to the smaller and larger tubes, respectively, and then combined at the other end of the smaller tube located in the larger tube, generating annular and sluggish flows in the water–acetonitrile–ethyl acetate ternary mixed solution (2:5:3 and 2:4:3 (v/v/v), respectively). The annular flow comprised the organic solvent-rich inner and water-rich outer phases and the sluggish flow comprised the organic solvent-rich sluggish domain and water-rich continuous phases. A model analyte mixed solution of 1-naphthol (hydrophobic) and 2,6-naphthalenedisulfonic acid (hydrophilic) were injected into the smaller tube and proceeded to the annular or sluggish flow in the larger tube, where they were separated and detected in that order. As observed, the annular and sluggish flows in the microspace could be used for separation without any specific treatments such as tube packing or coating.

Simultaneous determination of mequindox, quinocetone, and their major metabolites in chicken and pork by UPLC–MS/MS

This report presents a UPLC–MS/MS method for determination of mequindox (MEQ), quinocetone (QCT) and their 11 metabolites in chicken and pork samples. Following extraction process with acetonitrile–ethyl acetate, acidulation, and re-extraction with ethyl acetate in turn, target analytes were further purified using C18 solid phase extraction (SPE) cartridges for UPLC–MS/MS analysis. Validation was processed with mean recoveries from 69.1% to 113.3% with intra-day relative standard deviation (RSD) <14.7%, inter-day RSD <19.2%, and limit of detection between 0.05 and 1.0μg/kg for each analytes. The verified method was successfully applied to the quantitative determination of commercial samples. This developed procedure will help to control food animal products with MEQ and QCT residues, and facilitate further pharmacokinetic and residue studies of similar quinoxaline-1,4-dioxide veterinary drugs.

Development of a simple method for simultaneous determination of nine subclasses of non-steroidal anti-inflammatory drugs in milk and dairy products by ultra-performance liquid chromatography with tandem mass spectrometry

A multi-residue analysis method for simultaneous determination of nine subclasses of non-steroidal anti-inflammatory drugs (NSAIDs) in milk and dairy products by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) has been established. The sample was initially extracted and deproteinized with ascorbic acid buffer (0.01M, pH 3) and acetonitrile-ethyl acetate mixture, followed by centrifugation and evaporation, then reconstituted with acetonitrile-0.1% formic acid (1+1, v/v). After removal of lipid material by n-hexane, the sample was analyzed by UPLC-MS/MS with electro-spray ionization (ESI) interface in Multiple Reaction Monitoring (MRM) mode. The range of limits of detection (LODs) and limits of quantification (LOQs) were 0.03-0.30μg/kg and 0.10-1.00μg/kg, respectively. The recoveries in milk, milk powder, yogurt, processed cheese and milk beverage ranged from 61.7% to 117%, and the relative standard deviations (RSDs) were less than 17.9% at three spiked levels (1, 10 and 100 times of the LOQ). Matrix effects were also investigated and it was determined the signals of the analytes were suppressed from 9.4% to 76.6% in processed cheese. The proposed method was also applied to incurred sample analysis. The results proved that this method was suitable for the simultaneous determination of nine subclasses of NSAIDs residues in milk and dairy products.

Preparative separation and purification of flavonoids and stilbenoids from Parthenocissus tricuspidata stems by dual-mode centrifugal partition chromatography

We successfully used dual-mode centrifugal partition chromatography (CPC) to separate and purify major components from an ethyl acetate extract of Parthenocissus tricuspidata stems. Dual-mode CPC with a solvent system composed of ethyl acetate–acetonitrile–water (3:3:4, v/v) was performed in reverse-phase mode followed by normal-phase mode, through the use of a switching valve from descending to ascending mode. In reverse-phase mode (descending mode), more polar components such as aromadendrin-3-O-β-d-glucopyranoside (1), trans-piceid (2), and catechin (3) were isolated. Switching to normal-phase mode (ascending mode) yielded the less polar compounds, resveratrol (4) and engeletin (5). As a result, five major compounds, aromadendrin-3-O-β-d-glucopyranoside (46.6mg), trans-piceid (13.5mg), catechin (42.0mg), resveratrol (13.9mg), and engeletin (17.6mg), were isolated from 500mg of P. tricuspidata ethyl acetate extract. The purity of each isolated compound was determined to be 95% (1), 85% (2), 90% (3), 90% (4) and 95% (5) based on the HPLC peak areas.

Complexation ability of kryptofix 22DD with lanthanum (III) cation in some binary mixed non-aqueous solvents

The complex formation between lanthanum (III) cation with kryptofix 22DD was studied in acetonitrile–dimethylformamide (AN–DMF), acetonitrile–methanol (AN–MeOH), acetonitrile–ethylacetate (AN–EtOAc) and acetonitrile–ethanol (AN–EtOH) binary solvent solutions at different temperatures by using conductometric method. The conductance data show that in all cases, the stoichiometry of the complex formed between the macrocyclic ligand and the metal cation is 1:1 [ML]. The stability order of (kryptofix 22DD.La)3+ complex in the studied binary solvent solutions at 25 °C was found to be: AN–EtOAc>AN–EtOH>AN–MeOH>AN–DMF and in the case of pure non-aqueous solvents at 25 °C was: EtOAc>EtOH>MeOH>AN>DMF. A non-linear behavior was observed for changes of logKf of (kryptofix 22DD.La)3+ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the preferential solvation of the species involved in the complexation reaction. The values of standard thermodynamic parameters (∆H c°, ∆S c°) for formation of (kryptofix 22DD.La)3+ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots.The results show that in most cases, the (kryptofix 22DD.La)3+ complex is enthalpy destabilized, but entropy stabilized and the values of these thermodynamic quantities for formation of the complex are quite sensitive to the nature and composition of the mixed solvents solution.

Chromatography Using Ternary Water–Acetonitrile–Ethyl Acetate Mixture as a Carrier Solution on a Microchip Incorporating Microchannels

Abstract An open-tubular capillary chromatography system has been developed using a ternary mixed solvent solution, i.e., water–hydrophilic/hydrophobic organic solvent mixture as a carrier solution. The system is called “tube radial distribution chromatography (TRDC).” In this study, we tried to carry out the TRDC on a microchip incorporating microchannels. A model analyte solution of isoluminol isothiocyanate (ILITC) and ILITC-labeled bovine serum albumin (BSA) was injected to the double T-junction part (0.5 mm length, ca. 2 nL) on the microchip. The analyte solution was then delivered in the separation microchannel (40 µm in depth, 100 µm in width, and 22 cm in length) with a ternary water–acetonitrile–ethyl acetate mixture carrier solution (3:8:4, volume ratio). The model analytes, the ILITC and the labeled BSA were separated through the microchannel, where the carrier solvents were radially distributed in the separation channel generating inner and outer phases. This phenomenon of the solvents is called “tube radial distribution phenomenon (TRDP).” The outer phase functions as a pseudo-stationary phase under laminar flow conditions in the chromatography, i.e., TRDC. Finally, the ILITC and the labeled BSA were eluted in this order and detected with chemiluminescence reaction.

Complexing ability of kryptofix5 with Ag+ in some binary mixed solvents at different temperatures

The stability constant (log Kf ) for complexation of 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix5) with Ag+ has been determined conductometrically in acetonitrile–ethyl acetate (AN–EtOAc), methanol–ethyl acetate (MeOH–EtOAc), methanol–water (MeOH–H2O) and dimethyl sulfoxide–ethyl acetate (DMSO–EtOAc) solutions at different temperatures. A 1 : 1 [ML] complex was formed between the metal cation and ligand in most solvent systems. The stability constant of the resulting 1 : 1 complex was determined from computer fitting of the conductance–mole ratio data. The stability order of the (kryptofix5.Ag)+ complex in the studied binary mixed solvent solutions at 25°C was found to be MeOH–EtOAc > AN–EtOAc > DMSO–EtOAc. The results show that in some cases the stoichiometry of the complex formed between Ag+ and the ligand changes with the nature of the solvent and that solvation numbers of the metal cation and the resulting complexes change with temperature. The values of the standard thermodynamic parameters (, ) show that in all cases the (kryptofix5.Ag)+ complex is entropy stabilized, but the enthalpy, depending on solvent system, is stabilizing or destabilizing.

Influence of Adding Surfactants to an Analyte Solution on Separation Performance in Open-tubular Capillary Chromatography Based on the Tube Radial Distribution of Ternary Mixed Carrier Solvents

Abstract An open-tubular capillary chromatography system has been developed using a ternary mixed solvent mixture, i.e., water–hydrophilic/hydrophobic organic solvent mixture as a carrier solution. In this study, the influence of adding surfactants to an analyte solution on separation performance was examined in a chromatographic system using a fused-silica capillary tube (75 µm inner diameter and 100 cm effective length) and a ternary mixture of water–acetonitrile–ethyl acetate (3:8:4 volume ratio) carrier solution. Sodium dodecyl sulfate (anionic), ethylhexadecyldimethylammonium bromide (cationic), and Triton X-100 (nonionic) were used as surfactants. Model analytes, 1-naphthol and 2,6-naphthalenedisulfonic acid, were separated in this order by adding the anionic and nonionic surfactants. These surfactants in the analyte solution greatly improved the separation performance (theoretical plate numbers for 2,6-naphthalenedisulfonic acid; &amp;gt;10000) compared with the same separation performed in the absence of surfactants. On the other hand, the analytes were not separated at all using a cationic surfactant.

The Micro-Flow Reaction System Featured the Liquid–Liquid Interface Created with Ternary Mixed Carrier Solvents in a Capillary Tube

A micro-flow reaction system was developed in which liquid-liquid interface was created based on the tube radial distribution of ternary mixed carrier solvents. The system was constructed from double capillary tubes having different inner diameters (100 and 250 µm i.d.). The smaller tube was inserted into the larger one through a T-type joint. The reaction of a protein with a fluorescence derivatizing reagent was adopted as a model. A water-acetonitrile mixture (3:1 volume ratio) including bovine serum albumin (hydrophilic) was delivered into the large tube from the inside through the small tube and an acetonitrile-ethyl acetate mixture (7:4 volume ratio) containing fluorescamine (hydrophobic) as a derivatizing reagent was delivered from the outside through the joint. Solutions were mixed through the double capillary tubes to promote ternary mixed carrier solvents (water-acetonitrile-ethyl acetate; 1:2:1 volume ratio). The liquid-liquid interface was created based on the tube radial distribution of ternary solvents in the larger tube. The derivatization reaction was performed in the larger, or reaction, tube in the micro-flow system. The fluorescence intensity of the fluorescamine-derivatized bovine serum albumin obtained by the system, which specifically included the kinetic liquid-liquid interface in the tube, was greater than that obtained through a batch reaction using a homogeneous solution of water-acetonitrile (1:2 volume ratio).

Mixing Process of Ternary Solvents Prepared through Microchannels in a Microchip under Laminar Flow Conditions

The mixing process of ternary solvents (water-hydrophilic/hydrophobic organic mixture) prepared in microchannels in a microchip was examined by fluorescence observation of the dyes dissolved in the solvents under laminar flow conditions. A microchip incorporating microchannels was used. In it, three narrow channels were combined to form one wide channel. Water-acetonitrile (hydrophilic) mixture containing relatively hydrophilic Eosin Y (green) was fed into the narrow center channel and an acetonitrile-ethyl acetate (hydrophobic) mixture containing hydrophobic perylene (blue) was fed into the two narrow side channels in the microchip. The mixtures in the narrow channels combined in the wide channel to prepare the ternary solvents of water-acetonitrile-ethyl acetate, causing the tube radial distribution of the solvents. We observed the mixing process of the ternary solvents in the wide channel through fluorescence of the green and blue dyes, including an aqueous-organic interface. For example, the green dye that was fed into the center channel was distributed near the inner side walls and the blue dye that was fed into the two side channels was distributed around the center area in the wide channel. Such specific mixing behavior was not observed for two-component solvents in the wide channel, such as water-acetonitrile mixture and water-ethyl acetate mixture.

Biomolecule Analyses in an Open-Tubular Capillary Chromatography Using Ternary Mixed Carrier Solvents with Chemiluminescence Detection

We examined the elution behavior of isoluminol isothiocyanate (ILITC)-labeled biomolecules (α-amino acids, peptides, and proteins) in an open-tubular capillary chromatography system using an untreated fused-silica capillary tube and a water-acetonitrile-ethyl acetate mixture carrier solution. Such an open-tubular capillary chromatography is called "tube radial distribution chromatography (TRDC)" for convenience. A mixture of ILITC and ILITC-labeled biomolecules was analyzed using TRDC with chemiluminescence detection that provided simple instrument without a light source and complex optical devises. The ILITC and the labeled twenty α-amino acids were separated, in this order or the reverse order, or not separated with an organic solvent-rich and water-rich carrier solution. Their elution behavior was considered to be of hydrophilic or hydrophobic nature of ILITC and the labeled α-amino acids. The ILITC and the labeled protein, alcohol dehydrogenase and bovine serum albumin, were separated in this order with an organic solvent-rich carrier solution, while they were eluted in the reverse order with a water-rich carrier solution, based on the TRDC separation performance. The TRDC system worked with the untreated open-tubular capillary tube not using any specific capillary tubes, such as coated, packed, or monolithic.

Effects of Tube Materials on Capillary Chromatography Based on Tube Radial Distribution of Ternary Mixture Carrier Solvents under Laminar Flow Conditions

A capillary chromatography system was developed using an open capillary tube and a ternary solvents carrier solution of water-hydrophilic/hydrophobic organic solvent mixture. The chromatography is called a tube radial distribution chromatography (TRDC) system. The TRDC system works without applying high voltages or using specific columns, such as monolithic and packed columns. In this study, the effects of tube materials on separation performance were examined in the TRDC system, by using poly(tetrafluoroethylene) (PTFE; 100–400 μm inner diameter), polyethylene (PE; 200 μm inner diameter), and copolymer of (tetrafluoroethylene–perfluoroalcoxyethylene) (PTFE–PFAE; 100 μm inner diameter) capillary tubes. An analyte solution of 2,6-naphthalenedisulfonic acid and 1-naphthol as a model was subjected to the system with a water–acetonitrile–ethyl acetate carrier solution; 15:3:2 volume ratio (water-rich carrier) and 3:8:4 volume ratio (organic solvent-rich carrier). The flow rates were adjusted to be 0.5 μL min−1 for PTFE and PTFE–PFAE tubes as well as 2.0 μL min−1 for PE tube under laminar flow conditions. These analytes in the solution were separated in this order with the water-rich carrier solution with baseline separation in the three capillary tubes, while they were eluted in the reverse order or not separated with the organic solvent-rich carrier solution. The effects of tube temperature on separation were also examined with the water-rich carrier solution; the best resolutions were observed at 0 °C of the tube temperature. The obtained results were compared with those of fused-silica capillary tube and discussed.

Ion Exchange Solid Phase Extraction Coupled with Liquid Chromatography Tandem Mass Spectrometry for Determination of 8 Classes of Non-steroidal Anti-inflammatory Drugs Residues in Animal Tissues

An ultraperformance liquid chromatography tandem mass spectrometric(UPLC-MS/MS) method was established for the simultaneous determination of residues of 8 classes of 14 non-steroidal anti-inflammatory drugs(NSAIDs) in animal tissues.The samples were extracted with acetonitrile-ethyl acetate(1 ∶ 1,V/V),defatted with n-hexane,and then purified by MCX solid phase extraction(SPE) cartridge.Analysis was carried out on UPLC-ESI-MS/MS working with multiple reaction monitoring mode with polarity switching.Limits of detection were between 3.0 μg/kg and 10.0 μg/kg,and limits of quantification were between 10.0 μg/kg and 25.0 μg/kg.At spiked levels of 10.0-1000.0 μg/kg,in bovine and swine muscle the recoveries were 62.9%-108.4% and 63.4%-117.0%,respectively,and relative standard deviations(RSD) of the method were less than 10% and 9%,respectively.

Separation of dansyl-dl-amino acids by open tubular capillary chromatography based on tube radial distribution phenomenon of the ternary mixed carrier solvents

Separation of enantiomers, dansyl-DL-amino acids, was carried out by open-tubular capillary chromatography based on the tube radial distribution of the carrier solvents. An untreated poly(tetrafluoroethylene) capillary tube (100 μm inner diameter and 90 cm effective length) as a separation column and a water–acetonitrile–ethyl acetate mixture containing cyclodextrin as a carrier solution were used in the chromatography. An analyte solution of dansyl-DL-amino acids, such as dansyl-DL-methionine, was injected into the capillary tube by a gravity method. The analyte solution was subsequently delivered through the capillary tube with the carrier solution by a microsyringe pump. The ternary mixed carrier solution (water-rich carrier solution) was radially distributed in the capillary tube based on the tube radial distribution phenomenon, causing the formation of inner (water-rich) and outer (organic solvent-rich) phases. The outer or capillary wall phase acted as a pseudo-stationary phase in the chromatography. The analytes were separated through the capillary tube with on-capillary detection by an absorption or a fluorescence detector. The D-enantiomer and the L-enantiomer were eluted in this order with a baseline separation. The separation mechanism of the enantiomers in the open-tubular capillary using cyclodextrin was discussed.

Specific microfluidic behavior of ternary mixed carrier solvents of water–acetonitrile–ethyl acetate in open-tubular capillary chromatography and the chromatograms

We have developed a capillary chromatography system using an open-tubular capillary tube and a ternary water–hydrophilic–hydrophobic organic mixture carrier solution. We call the system “tube radial distribution chromatography (TRDC) system”. In this study, fluorescence photographs of the dyes dissolved in the ternary mixed carrier solvents in the TRDC were examined under various conditions concerning the inner diameters, tube temperatures, tube effective lengths, and flow rates (or average linear velocities). The TRDC system used an untreated fused-silica capillary tube and a ternary water–acetonitrile–ethyl acetate mixture carrier solution (3 : 8 : 4 volume ratio; the organic solvent-rich solution). The tube radial distribution of the carrier solvents that generated the organic solvent-rich major inner phase and the water rich minor outer phase could be observed in 50–700 μm inner diameters of the tubes at an average linear velocity of 11 cm min−1 through the fluorescence microscope–CCD camera. The model analyte solution of 1-naphthol, 1-naphthalenesulfonic acid, 2,6-naphthalenedisulfonic acid, and 1,3,6-naphthalenetrisulfonic acid was subjected to TRDC. They were separated and detected in this order with 50, 75, and 100 μm inner diameters of the open-tubular capillaries.