Reversed-phase Mode Research Articles

Fabrication process development and basic evaluation of eggshell-based column packing material for reversed-phase preparative separation

Purification of basic drugs in reversed-phase mode is often difficult, mainly due to adsorption of positively charged compounds to the silica gel-based stationary phase. Since this adsorption can be suppressed under alkaline condition, columns with alkali-resistance are required. In addition, compounds with acid-sensitive structures are sometimes degraded during separation on silica gel-based columns which exhibit acidity due to their surface structure. We prepared an alkali-resistant reversed-phase packing material, Eggshell-PMAcO based on eggshells modified with an amphiphilic copolymer, poly(maleic acid-alt-1-octadecene) (PMAcO). The height equivalent to a theoretical plate (HETP) of the Eggshell-PMAcO column was improved by surface treatment with ammonium acetate buffer (900 mM, pH = 3.7), which is an inexpensive reagent, and the retention behavior for hydrophobic compounds was compared to a typical ODS column based on silica gel, resulting in sufficient selectivity of the eggshell-based column for hydrophobic compounds, as indicated by the ratio of retention factors of pentylbenzene and butylbenzene (Eggshell-PMAcO column: 1.55, ODS column: 1.65). Column temperature-dependent retention behavior of naphthalene was investigated in the temperature range from 25 °C to 45 °C, followed by the calculation of thermodynamic parameters. There was little difference in the standard molar enthalpy (Eggshell-PMAcO: −19.6 kJ/mol, ODS: −21.7 kJ/mol). The absolute value of the standard free Gibbs energy for the Eggshell-PMAcO column was much smaller than that of the ODS column (Eggshell-PMAcO: −0.284 kJ/mol, ODS: −13.0 kJ/mol), indicating that the Eggshell-PMAcO column had a weaker retention strength for naphthalene than the ODS column mainly due to the large difference in the standard molar entropy (Eggshell-PMAcO: −64.9 J/mol K, ODS column: −29.2 J/mol K). The retention capacities for imipramine under neutral (water/methanol) and alkaline (0.1% triethylamine water/methanol) conditions were 0.2 mg and 5 mg, respectively, based on injection mass-dependent HETP, retention factor and symmetry factor. Finally, the prepared column was applied to the purification of a building block for nucleic acid drugs. This study demonstrated that reversed-phase columns, which can be fabricated from eggshells and an amphiphilic copolymer in an inexpensive and eco-friendly way, have the ability to purify basic compounds and acid-sensitive compounds.

Characterization and Classification of Spanish Honey by Non-Targeted LC–HRMS (Orbitrap) Fingerprinting and Multivariate Chemometric Methods

A non-targeted LC-HRMS fingerprinting methodology based on a C18 reversed-phase mode under universal gradient elution using an Orbitrap mass analyzer was developed to characterize and classify Spanish honey samples. A simple sample treatment consisting of honey dissolution with water and a 1:1 dilution with methanol was proposed. A total of 136 honey samples belonging to different blossom and honeydew honeys from different botanical varieties produced in different Spanish geographical regions were analyzed. The obtained LC-HRMS fingerprints were employed as sample chemical descriptors for honey pattern recognition by principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA). The results demonstrated a superior honey classification and discrimination capability with respect to previous non-targeted HPLC-UV fingerprinting approaches, with them being able to discriminate and authenticate the honey samples according to their botanical origins. Overall, noteworthy cross-validation multiclass predictions were accomplished with sensitivity and specificity values higher than 96.2%, except for orange/lemon blossom (BL) and rosemary (RO) blossom-honeys. The proposed methodology was also able to classify and authenticate the climatic geographical production region of the analyzed honey samples, with cross-validation sensitivity and specificity values higher than 87.1% and classification errors below 10.5%.

Effect of mobile-phase modifiers on the enantioselective retention behavior of methyl mandelate with an amylose 3,5-dimethylphenylcarbamate chiral stationary phase under reversed-phase conditions.

In this study, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, acetone, and tert-butanol were used as organic modifiers in reversed-phase mode chiral liquid-chromatography to systematically investigate the effects of mobile phase components on the enantioselective retention behavior of methyl mandelate with immobilized amylose 3,5-dimethylphenylcarbamate-based sorbent called Chiralpak IA. A two-site enantioselective model was used to obtain information on the recognition mechanisms by observing the dependence of the enantioselectivity and retention factor difference on the modifier content. Similar enantioselective retention behaviors were observed for all modifiers, and characteristic modifier concentration points (PL , PM , and PH ) were identified. At modifier concentrations up to PM , the weakened hydrophobic environment resulted in polymer structural relaxation, which changed the recognition mechanisms. By contrast, at concentrations beyond PH , considerably different enantioselectivity behaviors were observed, indicating that the existence of dipole-dipole interaction, which was stronger at higher modifier concentrations, contributed to the retention mechanisms. The concentrations at which these characteristic points occurred were dependent on the carbon number of the modifier molecule. Modifiers with more carbon numbers facilitated the transition in the enantioselective behaviors. These results demonstrated that the proposed method can provide a physically consistent quantitative description of enantioselective retention behavior in reversed-phase mode.

STUDIES IN DEVELOPMENT, VALIDATION AND APPLICATION OF ANALYTICAL RP-HPLC METHOD FOR QUANTITATIVE ESTIMATION OF GLIPIZIDE FROM ITS BULK AND FORMULATION

A RP-HPLC method has been developed for the estimation of glipizide (GLP). The proposed method is based on the separation of the drug in reversed-phase mode using BDS HYPERSIL C18 (4.6 mmø×250 mm) analytical column, mobile phase methanol:water 70:30 V/V, at the flow rate of 1.0 mL min-1 and detection wavelength 222 nm. GLP was well resolved and retained at t = 3.86 minutes. This RP-HPLC method was validated as per the recommendations of ICH Revised Q2(R1) guidelines of analytical method validation, in order to prove that the new analytical method meets the reliability characteristics. The method characteristics showed the capacity of an analytical method to keep, all over the time, the basic standards for validation: selectivity, linearity, precision, accuracy and sensitivity. The method was found linear over the range 1-7 µg mL-1. The LOD and LOQ were 0.5281 and 1.761 µg mL-1 for GLP. The validated method was successfully used for quantitative estimation(assay) of GLP from in-house formulation and marketed formulations.

“Click” preparation of a chiral macrocycle-based stationary phase for both normal-phase and reversed-phase high performance liquid chromatography enantioseparation

Chiral polyimine macrocycles (CPMs) constitute a new family of organic macrocycles that have defined cavities, rigid shapes, inherent chirality and multiple cooperative binding sites, and have shown great potential in diverse areas. However, the application of CPMs for high performance liquid chromatography (HPLC) enantioseparation has rarely been reported. In this work, a novel chiral stationary phase (CSP) for HPLC was prepared by chemical bonding of a CPM (C54H72N6O3) onto thiolated silica via thiol-ene click reaction. The CSP exhibited good enantioselectivity in both normal- and reversed-phase HPLC. Chiral compounds included alcohols, diols, ketones, organic acids, esters, ethers, amines, and epoxides were enantioseparated on the column in normal-phase mode (17 compounds) and reversed-phase mode (20 compounds). Importantly, broader chiral resolution was observed with the column than that obtained using our previously studied chiral macrocycle H3L-based column, indicating the potential to significantly improve and broaden applicability of this novel macrocycle-type CSPs. Moreover, the CSP exhibited good complementary enantioseparation to Chiralpak AD-H and Chiralcel OD-H columns, enabling separation of some racemates that could not be separated by the two popular chiral HPLC columns. In addition, the fabricated column exhibited good stability and reproducibility. The relative standard deviations (RSDs) (n = 5) of retention time and resolution after multiple injections were < 0.20 % and < 0.39 %, respectively. The results demonstrated the great potential of this type of CPM for HPLC separation of enantiomers.

Stability Indicating Assay Method for the Quantitative Determination of Olaparib in Bulk and Pharmaceutical Dosage Form.

Olaparib is an orally active poly (ADP-ribose) PARP (polymerases) inhibitor known to destroy cancer cells with BRCA1 or BRCA2 deficiency. An authentic, fast, distinct, and reliable reverse phase-high performance liquid chromatography (RP-HPLC) method was developed and promptly validated in tablet formulations for olaparib estimation. The proposed method focuses on the separation of olaparib in reverse phase mode using a Waters symmetry C18 (150 x 4.6 mm, 5 μm) analytical column with a flow rate of 1.0 mL/min and the injection volume was kept at 20 μL. The optimized mobile phase consists of ammonium acetate buffer (pH adjusted to 3.5 by glacial acetic acid): methanol in the ratio of 50:50 v/v. The eluents were measured at 254 nm and the retention time for the drug encircled was about 4.32 min. The stress degradation studies of olaparib were conducted under acidic, alkaline, oxidative, photolytic and thermal conditions to demonstrate the stability of the drug. The regression value of 0.998 showed that the developed method was linear over the range of 80 μg/mL to 120 μg/mL. The developed RP-HPLC method is accurate and precise. The method was statistically validated as per International Conference on Harmonization guidelines. The proposed method is suitable and can be applied for the quantitative estimation of olaparib without any interference of the excipients used in the drug formulations.

Monomer-mediated fabrication of microporous organic network@silica microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography

Microporous organic networks (MONs) are promising in high performance liquid chromatography (HPLC) with large specific surface area, good hydrophobicity and stability. However, their superhydrophobic structures restrict MONs-based HPLC only in reversed-phase mode. To decrease the hydrophobicity of pristine MONs and to expand their broad application in HPLC, here we described the monomer-mediated fabrication of core-shell MON-2COOH@SiO2 microspheres for reversed-phase liquid chromatography (RPLC)/hydrophilic interaction liquid chromatography (HILIC) mixed-mode chromatography for the first time. The –COOH groups were introduced into MONs’ skeleton to improve their hydrophilicity and to provide hydrophilic interaction sites. The MON-2COOH was grafted onto silica via a monomer mediated method to produce monodispersed core-shell microspheres. By adjusting the concentration of reactants, the thickness of MON-2COOH shell was easily manipulated. The packed MON-2COOH@SiO2 column showed high resolution and selectivity for separating both hydrophobic (alkylbenzenes, polycyclic aromatic hydrocarbons, anilines and phenols) and hydrophilic (nucleoside and nucleic bases) probes, highlighting the promise of MONs in mixed-mode HPLC. The MON-2COOH@SiO2 column also achieved good separation to sulfonamides, nonsteroidal anti-inflammatory drugs, flavonoids and phenylurea herbicides, and offered better resolution than commercial C18 and pristine SiO2 column. Multiple retention mechanisms were also found on MON-2COOH@SiO2 packed column, underlining the great potential of MONs in mixed-mode HPLC.

Comparing the chromatographic performance of benzene and aniline end capped stationary phase synthesized by click chemistry

Two stationary phases named Sil-styrene and Sil-PAS were synthesized using styrene and p-aminostyrene as end capped functional monomers by the reaction of click chemistry, respectively. Intermediates and stationary phase materials were characterized by various methods. Four types of compounds including polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, positional isomers, nucleotides and nucleosides were chosen to assess reversed-phase and hydrophilic interaction separation modes of two prepared columns. Retention mechanism of these analytes was researched through investigating effects of mobile phase composition on retention. Prepared columns could achieve better separation effects including higher resolution, shorter retention time and less organic solvent compared with traditional commercial columns. Moreover, the PAHs in barbecued meat samples was achieved separation under the reverse-phase mode on the Sil-styrene column. The experimental results shows that amino groups on the benzene ring can affect the hydrophilic and hydrophobic interactions with analytes, and the prepared Sil-styrene column shows enormous potential for separation of PAHs in actual samples.

Preparation of chiral stationary phase based on a [3+3] chiral polyimine macrocycle by thiol-ene click chemistry for enantioseparation in normal-phase and reversed-phase high performance liquid chromatography

Polyimine macrocycles are a new class of organic macrocycles with cyclic structures, well-defined molecular cavities, and multiple cooperative binding sites, which have recently aroused considerable research interest in molecular recognition and separation. Herein, we report the bonding of a [3+3] chiral polyimine macrocycle (H3L, C78H78N6O3) on thiol-functionalized silica gel using thiol-ene click chemistry to prepare a chiral stationary phase (CSP) for high performance liquid chromatography (HPLC). The fabricated column exhibited excellent chiral separation capability under both normal-phase and reversed-phase conditions. Fourteen and 10 racemates were well resolved on the column in normal-phase mode (using n-hexane/isopropanol as the mobile phase) and reversed-phase mode (using methanol/water as the mobile phase), respectively, including alcohols, esters, ethers, ketones, aldehydes, epoxides and organic acids. Moreover, the column also shows good selectivity toward positional isomers. Six positional isomers (dinitrobenzene, chloroaniline, bromoaniline, iodoaniline, nitrobrobenzene and nitrochlorobenzene) were well separated on the column. In addition, the effects of the injection mass and mobile phase composition on the separation were investigated. The column shows good reproducibility and stability after multiple injections with the relative standard deviation (RSD) (n = 5) of the retention time and resolution being < 0.96 % and 0.65 %, respectively. This study indicates that this type of chiral polyimine macrocycles is a promising chiral selector for HPLC enantioseparation and will push forward the applications of more novel chiral macrocycles for chiral chromatographic separation.

Benefits of a Mixed-Mode Stationary Phase to Address the Challenging Purification of an Industrially Relevant Peptide: A Proof-of-Concept Study

Peptides are a class of biomolecules with a great potential from the therapeutic point of view, because of their unique biological properties. Industrially, the production stategies adopted produce both the target peptide and a series of impurities that must be removed. Preparative chromatography is the technique of choice for the large-scale purification of biomolecules, generally performed in reversed-phase mode, using hydrophobic adsorbents (e.g., C8 stationary phases). A promising and innovative alternative is represented by mixed-mode columns, which bear two different ligands on the particle surface, exploiting two different retention mechanisms to improve the separation. This work represents a proof-of-concept study focused on the comparison of a hydrophobic adsorbent and a mixed-mode one (bearing both hydrophobic groups and charged ones) for the purification of a crude peptide mixture. Thanks to more-favourable thermodynamics, it was found that, when collecting the whole peak excluding fractions of the peak tail, the mixed-mode column led to an increase in the recovery of roughly +15%, together with a slight improvement in purity at the same time, with respect to the traditional hydrophobic column. In addition, if the whole peak, including the tail, is collected, the performance of the two columns are similar in terms of purity and recovery, but the pepetide elutes as a narrower peak with the mixed mode. This leads to a collection pool showing a much-higher peptide concentration and to lower solvent volumes needed, which is a beneficial achievement when targeting more sustainable processes. These results are very advantageous from the industrial viewpoint, because they also involve a decrease in the peptide amount contained in the peak tail, which must be reprocessed again to satisfy purity requirements.

Determination of Chiral Impurity of Naproxen in Different Pharmaceutical Formulations Using Polysaccharide-Based Stationary Phases in Reversed-Phased Mode.

A novel, validated, reversed-phase (RP), chiral high performance liquid chromatography (HPLC) method was developed for the enantiopurity control analysis of naproxen, a frequently used non-steroidal anti-inflammatory agent using polysaccharide-type chiral stationary phase (CSP). In the screening phase of method development, seven columns were tested in polar organic (PO) mode using mobile phases consisting of 0.1% acetic acid in methanol, ethanol, 2-propanol, and acetonitrile. Enantiorecognition was observed only in five cases. The best enantioseparation was observed on a Lux Amylose-1 column with 0.1% (v/v) acetic acid in ethanol with a resolution (Rs) of 1.24. The enantiomer elution order was unfavorable, as the distomer eluted after the eutomer. When the ethanolic mobile phase was supplemented with water, enantiomer elution order reversal was observed, indicating a difference in the enantiorecognition mechanism upon switching from PO to RP mode. Furthermore, by changing ethanol to methanol, not only lower backpressure, but also higher resolution was obtained. Subsequent method optimization was performed using a face-centered central composite design (FCCD) to achieve higher chiral resolution in a shorter analysis time. Optimized parameters offering baseline separation were as follows: Lux Amylose-1 stationary phase, thermostated at 40 °C, and a mobile phase consisting of methanol:water:acetic acid 85:15:0.1 (v/v/v), delivered with 0.65 mL/min flow rate. Using these optimized parameters, a Rs = 3.21 ± 0.03 was achieved within seven minutes. The optimized method was validated according to the ICH guidelines and successfully applied for the analysis of different pharmaceutical preparations, such as film-coated tablets and gel, as well as fixed-dose combination tablets, containing both naproxen and esomeprazole.

Enantioselective high-performance liquid chromatography of aryl-substituted oxazolines as an efficient tool for determination of chiral purity of serine medicinal components.

A new approach for the evaluation of chiral purity of serine esterification products bearing long-chain alkyl substituents was developed. The compounds were simply converted to aryl-substituted oxazolines which: (i) facilitates effective chromatographic enantioseparation and (ii) enables direct detection using ultraviolet absorption. The method employs a polysaccharide-based chiral stationary phase and allows enantioseparation of highly stable oxazoline products in less than 6 min using a simple binary mobile phase. As opposed to the previously used normal phase method the developed method was performed in the reversed-phase mode. Aside from the benefits of switching to less hazardous solvents with regard to the principles of Green Chemistry, this has also led to a reduction in the analysis time. In comparison with known serine chromophores, the best enantioseparation of aryloxazoline rigid structure may be achieved only based on non-polar interactions with the chiral stationary phase. In contrast, the substitution of the chromophore moiety with hydroxyl substituent affected intra and intermolecular interactions that caused enantioseparation differences. Concurrently, we found high chirality retention of (R)- and (S)-configuration oxazoline standards (≥99% enantiomeric excess) during the introduction of the ultraviolet label. The method is suitable for rapid injection of the mixture containing the ultraviolet absorption marker without prior purification.

Separation of anilines by a covalent triazine-triphenyl polymer as a stationary phase for their normal-phase and reverse-phase determination by high-performance liquid chromatography (HPLC)

A covalent triazine-triphenyl polymer (CTPCC-TP) was examined as a novel column packing material for high-performance liquid chromatography (HPLC). The separation performance of CTPCC-TP was characterized using anilines as the analytes in reverse-phase (RP) and normal-phase (NP) modes. Various retention mechanisms, such as hydrogen-bonding, π-π, and hydrophobic-hydrophobic interactions, endowed CTPCC-TP with a hydrophilic-hydrophobic balance performance, demonstrating promise for applications as a stationary phase for HPLC in normal-phase and reversed-phase. The CTPCC-TP column showed good reproducibility with relative standard deviations from 0.28 to 0.93%, 1.73 to 3.12%, 1.57 to 3.69%, and 1.36 to 2.54% for retention time, peak height, peak area, and peak width at half maximum, respectively. In the normal and reverse phase modes, a thermodynamically spontaneous transfer process is demonstrated through negative ΔG values controlled by negative ΔH and ΔS values during the chromatographic separation. Excellent chemical and solvent stabilities, and the hydrophilic-hydrophobic balance performance make CTPCC-TP a good candidate for use in HPLC.

A New Benzyl Phenethanolamine-β-Cyclodextrin Bonded Phase: Chiral Chromatography Performance and Application for LC-MS/MS Analysis of Pesticide Enantiomers in Fruits and Vegetables.

At present, the research on achiral drug and pesticide residue detection methods is still the mainstay at home and abroad, and there is still a lack of systematic research on the enantiomeric analysis of chiral drugs and pesticides. In order to prepare a novel chiral stationary phase, whose "multi-mode" chiral separation chromatographic performance and its utility was verified. An S-(-)-2-benzylamino-1-phenylethanol mono-derivative β-cyclodextrin bonded stationary phase (BzCSP) was prepared based on the "thiol-ene" addition reaction. The chiral compounds including four types of chiral compounds were used as "probes," and their chiral chromatographic properties were evaluated. Furthermore, a new LC-MS/MS method for the determination of the enantiomeric residues of three chiral pesticides in five kinds of fruits and vegetables was established. The study found that the novel stationary phase was suitable for a variety of chromatographic modes (normal phase mode, reversed-phase mode, polar organic mode). The resolutions of hexaconazole (Hex), tebuconazole (Teb), and triticonazole (Trit) enantiomers could be up to 2.31, 1.68, and 1.48, respectively, within 30 min under reversed-phase chromatography. Based on the optimal chromatographic and mass spectrum conditions, a new LC-MS/MS quantitative method for the Hex, Teb, and Trit enantiomers was established by multi-reaction positive ion monitoring (MRM). The detection limits (LODs) of enantiomers were less than 0.89 µg/kg for Hex, 0.93 µg/kg for Teb, and 0.93 µg/kg for Trit, and the averaged recoveries of enantiomers were in the range of 75.8-106.3% for Hex, 77.4-116.3% for Teb, and 78.7-113.4% for Trit. The method had good reproducibility with the RSDs (<5%) for intraday and (<7%) for interday. The established method had the characteristics of good selectivity, high sensitivity, strong resistance to matrix interference, and good reproducibility. It is indicated that the stationary phase prepared by the "thiol-ene" addition reaction is a new type of multi-mode stationary phase, which has a good development value. The study reported a new method for the rapid preparation of a rare "multi-mode" chiral stationary phase BzCSP based on the "thiol-ene" addition reaction and verified the practicability of BzCSP including good selectivity, high sensitivity, strong resistance to matrix interference, and good reproducibility.

Development of a novel HPLC-ESI-MS/MS method to analyze the stereoselective pharmacokinetics and tissue distribution of isoconazole enantiomers in rats.

Isoconazole with an asymmetrical carbon is a broad-spectrum antimicrobial imidazole, but there is still lack of relevant report about the potential enantioselectivity in biological samples. The object of this research was to develop and validate a sensitive and effective high performance liquid chromatography-electrospray ionization coupled with tandem mass spectrometry (HPLC-ESI-MS/MS) method for stereoselective separation and determination of isoconazole enantiomers in Sprague-Dawley (SD) rat plasma and tissues. The greater enantioseparation of isoconazole enantiomers was obtained on a Chiralpak IC column with a mobile phase consisted of acetonitrile-10 mM aqueous ammonium acetate (90:10, v/v) under the reversed-phase mode. Subsequently, the studied compounds and internal standard (IS) were detected on a multiple reaction monitoring (MRM) mode with positive electrospray ionization source. The experimental and theoretical Electronic Circular Dichroism (ECD) spectra were employed to confirm the absolute configuration of isoconazole enantiomers. Eventually, after full method validation, the newly developed method was successfully applied to the study of enantioselectivity in plasma and tissues in SD rats. Results illustrated that the enantioselective differences in plasma were observed for the evidence that the concentrations of S-(-)-isoconazole were always higher than R-(+)-isomer. In terms of tissue distribution, liver, kidney, lung, spleen, and small intestine were the mainly distributed tissues and then followed by heart and muscle. This is the first study to reveal the stereoselective behavior of isoconazole enantiomers in vivo, which also provides reliable and valuable reference for further elucidating the enantioselective metabolisms of isoconazole enantiomers.

Preparation and evaluation of molding-type solid-phase extraction media binding with commercially available adhesives.

A fabrication method of molding-type solid-phase extraction media (M-SPEM) bound with commercially available adhesive is presented. Six pieces of M-SPEM were prepared by heating each kneaded product of a particulate sorbent and an adhesive inserted into a six-hole cylindrical mold for hardening under an open system and normal pressure. The particulate sorbent contained in M-SPEM was divinylbenzene-based reversed-phase mode solid-phase extractants that we have reported. An examination of several adhesives showed that the moldability of M-SPEM depended on the composition and properties of the adhesive. The optimized procedure can be used to prepare an M-SPEM containing an 85 wt% particulate sorbent (particulate sorbent/adhesive, 100mg/17mg; particle diameter, 90-150µm), and the M-SPEM has a specific surface area of about 500m2/g. The established procedure in this study can bind particulate sorbents together, which showed almost no reductions in the adsorption property and liquid permeability compared with those of the particulate sorbent.

Modification of magnetite-doped NH2-MIL-100(Fe) with aliphatic C8 carbon chain for feasible protein purification in reversed-phase mode

NH2-MIL-100(Fe) is a stable Metal-Organic Frameworks (MOFs) possessing numerous tunable properties. In this study, we have successfully modified NH2-MIL-100(Fe) with aliphatic C8 carbon chain to create a hydrophobic surface distribution. The detailed characterizations of NH2-MIL-100(Fe)-C8 were performed to demonstrate its attractive properties, such as unique MOF architecture, sufficient surface area, and surface hydrophobicity. In addition, the NH2-MIL-100(Fe)-C8 exhibited the distinctive hydrophobic interaction with an individual protein under a specific concentration of acetonitrile, and was able to separate the protein from a mixture with a good resolution. It has a binding capacity of 6.25 μg of BSA/mg particle. Since we have introduced Fe3O4 to NH2-MIL-100(Fe)-C8 to provide with excellent magnetization, the target protein could be easily collected by a magnet and the NH2-MIL-100(Fe)-C8 could be regenerated over 15 times without significant loss of its capacity. Therefore, NH2-MIL-100(Fe)-C8 provides researchers with a convenient and affordable tool for protein separation and purification in reversed-phase mode.

Sound field optimization and particle trapping of confocal ultrasonic transducer

The nonlinear effect of high-intensity sound waves produces the acoustic radiation force (ARF), which are used for acoustic levitation and manipulation practical. With no special requirement for the physical and chemical properties of the controlled objects, acoustic levitation owns a promising application prospect. The common levitation scheme includes the standing-wave system and phased-array levitation system. The standing-wave system has poor performance in the aspects of the degree of spatial freedom, the ARF along the non-axial direction, and the levitation stability. The phased-array system requires a complex control system and a high production cost. Here, we propose a single-side acoustic levitation system based on the paired confocal focused transducers. By driving the transducer pairs with reverse phase mode, two anti-phase focused spherical waves interfere with each other, resulting in constant sound pressure of 0 Pa at the focus. The resulting potential well can achieve stable particle capturing and levitating. First, we verifed the theoretical feasibility of the system according to Huygens' principle. Then, using the finite element method, we analyzed the influences of structural and driving parameters on the sound field distribution, such as the angle between the transducer axis and the central axis of the structure and the excitation phase modes. Finally, we demonstrated the particle trappings under two kinds of excitation phase modes of the levitation system experimentally. The results show that, 1) the intensity of the dominating potential well reaches a strongest value when the structural angle is 45°; 2) as the excitation phases are 0, 0, π, and π, the sound field owns three potential wells which can capture three clusters of quartz sands, the primary potential well is stronger than the secondary one; 3) as the excitation phases are 0, π/2, π, and 3π/2, the sound field owns one potential well and captures one cluster of quartz sands. The isosurface of wave intensity around the potential well is more comprehensive than in the previous phase mode. The four-phase excitation improves the levitation stability better. The proposed levitation scheme can realize stable single- or multi-position capture of high-density objects in the fluid. Moreover, it has the advantages of low cost and a high degree of freedom.

Simultaneous Determination of Escitalopram Impurities Including the R-Enantiomer on a Cellulose Tris(3,5-Dimethylphenylcarbamate)-Based Chiral Column in Reversed-Phase Mode

Simultaneous Determination of Escitalopram Impurities Including the R-Enantiomer on a Cellulose Tris(3,5-Dimethylphenylcarbamate)-Based Chiral Column in Reversed-Phase Mode

Stereoselective quantitative analysis of ranolazine in plasma and tissue samples: application in pharmacokinetics and tissue distribution studies

This study aimed to develop a rapid and sensitive reversed-phase mode high-performance liquid chromatography-electrospray ionization coupled with a tandem mass spectrometry method for the simultaneous determination of ranolazine enantiomers in rat plasma and tissues.