Separation Of Small Molecules Research Articles

A simulation-guided approach to the selection of RPLC columns for platform small molecule separations

Simulations were conducted to evaluate the potential of several hundred reversed-phase columns to separate small molecules. By calculating the retention factor of compounds in randomly generated virtual mixtures via the HSM (hydrophobic subtraction model) and applying basic chromatography theory, the simulation can estimate the retention time and peak width of every virtual compound and calculate the resolution between every adjacent pair of compounds. A preferred column set based on the number of successful separations of randomly generated virtual mixtures was developed. The tandem-column liquid chromatography (TC-LC) approach can separate 53.2 % of the 16-compound samples using 20 tandem-column pairs, while a single-column approach can only separate 42.6 % of the 16-compound samples with 20 single columns. The preferred set of columns obtained from the simulation was almost the same as the empirical set of columns previously obtained. In screening applications, TC-LC can achieve a comparably successful separation factor (selectivity) with a smaller column inventory (nine 50-mm columns) compared to the larger inventory needed by single-column LC (twenty-one 100-mm columns).

Hydrophilic Interaction Liquid Chromatography for the Analysis of Pharmaceutical Formulations

Abstract: For a long time, Reversed-Phase Liquid Chromatography (RPLC) was the most dominant technique for the analysis of pharmaceutical compounds, but with poor efficiency in the separation of small polar molecules. From the efforts to solve the problem of insufficient retention of these molecules, during the last decades, a mode of liquid chromatography named Hydrophilic Interaction Liquid Chromatography (HILIC) has experienced vast expansion. It is based on the use of a highly hydrophilic stationary phase along with an aqueous mobile phase with high organic modifier content. In this review, the characteristics of stationary and mobile phases used in HILIC are described, and corresponding separation mechanisms are discussed. An overview of recently published papers dealing with the application of HILIC in analyzing pharmaceuticals in biological and non-biological samples is provided. Besides, the application of HILIC systems in the determination of the physicochemical properties of compounds is described.

Micro/nanofluidic device for tamsulosin therapeutic drug monitoring in patients with benign prostatic hyperplasia at point of care.

Discovering the balance between toxicity and efficacy for many drugs requires therapeutic drug monitoring (TDM) of their concentrations in the blood. Here, a hot-embossed microfluidic device with a new design integrated to a nanofracture is presented for purification of blood samples from numerous proteins and cells, allowing to the separation of small molecules from blood matrix. The device was used to separate and quantitatively detect tamsulosin drug after derivatization with fluorescamine reagent, allowing converting it from a neutral molecule into a charged fluorescent complex under the experimental conditions, and thus its separation by electrophoresis. The device is portable and easy operated, and the presented method showed good linearity (R2 = 0.9948) over a concentration range of 0.1-1μg/mL. The relative standard deviation (RSD%) was below 10% (n = 3), indicating good precisions, and the limit of detection (LOD) and limit of quantitation (LOQ) values were estimated to be 0.1 and 0.55μg/mL, respectively. Whole blood samples from 10 patients with benign prostatic hyperplasia (BPH) were analyzed, showing good percentage recoveries of tamsulosin in whole blood. This point-of-care (POC), low-cost method could increase the convenience of patients and doctors, make therapies safer, and make TDM available in different regions and places.

Understanding the mechanism of permanganate ion rejection in TpPa-1/Ti3C2T2 composite membranes via molecular dynamic simulation

The purification and separation of small molecules can be improved by fabricating different composite membranes, in this work, the TpPa-1/Ti3C2T2 composite membranes with different structural parameters and terminating functional groups were designed for better permanganate (PP) ions separation with non-equilibrium molecular dynamics simulations. The rejection mechanism was explored from molecular level. It is found that water flux is mainly influenced by the offset and interlayer spacing of Ti3C2T2, while the rejection rate of PP ion is affected more by the slit width of MXene. The combination of TpPa-1 and Ti3C2(OH)2 membrane provides a comfortable zone in for PP ion rejection from the viewpoint of thermodynamic. While the other two composite membranes constructed with terminating functional groups (-F, –O) in Ti3C2T2 show different rejection mechanism from that in TpPa-1/Ti3C2(OH)2 composite membrane. The rejection of PP ions mainly caused by the dynamic hindrance caused by water wall formed in the entrance of Ti3C2T2 (T = –F, –O) slits.

Core-shell silica@pyridyl conjugated microporous polymer as a stationary phase for high performance liquid chromatography

BackgroundBecause of the advantages of good selectivity, high sensitivity, and fast analysis, high performance liquid chromatography (HPLC) has become one of the modern analytical techniques in wide application range, such as biological analysis, environmental detection, pharmaceutical and food inspection, agriculture and other fields. The stationary phase greatly decides the chromatographic separation performance, so the development of novel stationary phase is most important for HPLC. ResultsPyridyl conjugated microporous polymers (P-CMP) with one to four layers were modified on the surface of amino silica to obtain a novel core-shell material (SiO2@P-CMP) by the layer-by-layer assembly strategy and Chichibabin reaction. The relationship between the structure of SiO2@P-CMP and chromatographic performance was carefully investigated, and the retention mechanism was revealed. The interactions including π-π stacking, hydrophobic effect and hydrogen bond gradually enhanced with the increase of P-CMP layers on the silica surface. Compared with C18 column, SiO2@P-CMP columns displayed better separation selectivity for polycyclic aromatic hydrocarbons (PAHs). According to the relative retention values (α), the separation performance of SiO2@P-CMP columns (α = 1.144–1.884) for PAH isomers and other analytes was obviously better than that of C18 column (α = 0.998–1.487). Furthermore, the SiO2@P-CMP column with four layers was selected to separate different types of analytes (eight PAHs, four bisphenols, four estrogens and nine phthalates), and the peak order of analytes was different from that on the C18 column due to the influence of hydrogen-bonding and π-π interactions. The relative standard deviations (n = 10) of retention time and peak area on SiO2@P-CMP column were between 0.28 % and 1.98 %. Significance and noveltyPyridyl conjugated microporous polymer was introduced as the stationary phase for the first time in HPLC. The proposed column displayed better separation characteristics compared to Zorbax SB-C18 column. It provided a new idea for the separation of small molecules and the development of chromatographic packing or extraction material.

Channel confinement and separation properties in an adaptive supramolecular framework using an adamantane tecton

A supramolecular framework with adaptive channels based on an adamantane tecton enables confinement and separation of small molecules and petrochemicals.

A new universal detection system for high-performance thin-layer chromatography plates using chemiluminescence

High-performance thin-layer chromatography (HPTLC) is a cost-effective method for the separation of small molecules, such as active pharmaceutically ingredients. The method can be used without sophisticated equipment. For example, the detection and quantification of colored compounds on an HPTLC plate can be performed with a CCD camera. For noncolored compounds, a new dipping solution for the generation of chemiluminescence on an HPTLC plates is presented. In combination with a charge-coupled diode (CCD) camera, this can be used as a universal detection system. The efficiency of this new staining reagent is demonstrated by the detection of trimethoprim and sulfamethoxazole from a fixed-dose combination in a ratio of 1:5.

Dimethyl carbonate as a green alternative to acetonitrile in reversed-phase liquid chromatography. Part I: Separation of small molecules

Nowadays, environmental problems are drawing the attention of governments and international organisations, which are therefore encouraging the transition to green industrial processes and approaches. In this context, chemists can help indicate a suitable direction. Beside the efforts focused on greening synthetic approaches, currently also analytical techniques and separations are under observation, especially those employing large volumes of organic solvents, such as reversed-phase liquid chromatography (RPLC). Acetonitrile has always been considered the best performing organic modifier for RPLC applications, due to its chemical features (complete miscibility in water, UV transparency, low viscosity etc); nevertheless, it suffers of severe shortcomings, and most importantly, it does not fully comply with Environmental, Health and Safety (EHS) requirements. For these reasons, alternative greener solvents are being investigated, especially easily available alcohols.In this work, chromatographic performance of the most common solvents used in reversed-phase chromatography, i.e., acetonitrile, ethanol and isopropanol, have been compared to a scarcely used solvent, dimethyl carbonate (DMC). The analytes of interest were two small molecules, caffeine and paracetamol, whose kinetics and retention behaviour obtained with the four solvents have been compared, and all contributions to band broadening have been assessed. Results about kinetic performance are very promising, indicating that a small amount (7 % v/v) of DMC is able to produce the same efficiency as a 2.5-times larger ACN volume (18 % v/v), and larger efficiency than alcohols.This paper reports, for the first time, fundamental studies concerning the mass transfer phenomena when DMC is used as an organic solvent in RPLC, and, together with the companion paper, represents the results of a research whose final aim was to discover whether DMC is suitable for chromatographic applications both in linear and preparative conditions.

Advanced Metal–Organic Frameworks for Gas Separation

In the chemical process, the effective separation of small gaseous molecules with similar physical and chemical properties is of great significance. In addition, clean energy sources such as hydrogen and methane are regarded as an ideal alternative to conventional fossil fuels. However, at present, the storage technology of this kind of natural gas is not perfect. The entry of harmful substances produced by human activities into the atmosphere has become a global danger that is becoming more and more worrying. It has become an important topic for scholars and industries Development of a multi-stage channel structure with high efficiency and low energy consumption for effective separation, storage or capture of toxic and harmful substances. In order to solve this problem, we intend to study the adsorption and adsorption of MOFs in the environment aboutH2/N2, H2/CO and H2/CH4 and some other gases. Compared with molecular sieve, activated carbon and other conventional inorganic porous materials, MOFs have a broad application prospect in gas adsorption and storage with unique properties. At present, the research of metal-organic frame materials with high stability has made great progress. Through the implementation of this project, it is expected to promote its wide application in air pollution control and other aspects.

Chromogranin B (CHGB) is dimorphic and responsible for dominant anion channels delivered to cell surface via regulated secretion.

Regulated secretion is conserved in all eukaryotes. In vertebrates granin family proteins function in all key steps of regulated secretion. Phase separation and amyloid-based storage of proteins and small molecules in secretory granules require ion homeostasis to maintain their steady states, and thus need ion conductances in granule membranes. But granular ion channels are still elusive. Here we show that granule exocytosis in neuroendocrine cells delivers to cell surface dominant anion channels, to which chromogranin B (CHGB) is critical. Biochemical fractionation shows that native CHGB distributes nearly equally in soluble and membrane-bound forms, and both reconstitute highly selective anion channels in membrane. Confocal imaging resolves granular membrane components including proton pumps and CHGB in puncta on the cell surface after stimulated exocytosis. High pressure freezing immuno-EM reveals a major fraction of CHGB at granule membranes in rat pancreatic β-cells. A cryo-EM structure of bCHGB dimer of a nominal 3.5 Å resolution delineates a central pore with end openings, physically sufficient for membrane-spanning and large single channel conductance. Together our data support that CHGB-containing (CHGB+) channels are characteristic of regulated secretion, and function in granule ion homeostasis near the plasma membrane or possibly in other intracellular processes.

A SERS Composite Hydrogel Device for Point-of-Care Analysis of Neurotransmitter in Whole Blood

Point-of-care analysis of neurotransmitters in body fluids plays a significant role in healthcare improvement. Conventional approaches are limited by time-consuming procedures and usually require laboratory instruments for sample preparation. Herein, we developed a surface enhanced Raman spectroscopy (SERS) composite hydrogel device for the rapid analysis of neurotransmitters in whole blood samples. The PEGDA/SA composite hydrogel enabled fast separation of small molecules from the complex blood matrix, while the plasmonic SERS substrate allowed for the sensitive detection of target molecules. 3D printing was employed to integrate the hydrogel membrane and the SERS substrate into a systematic device. The sensor achieved highly sensitive detection of dopamine in whole blood samples with a limit of detection down to 1 nM. The whole detection process from sample preparation to SERS readout can be finished within 5 min. Due to the simple operation and rapid response, the device shows great potential in point-of-care diagnosis and the monitoring of neurological and cardiovascular diseases and disorders.

Peptide-derived coordination frameworks for biomimetic and selective separation.

Peptide-derived metal-organic frameworks (PMOFs) have emerged as a class of biomimetic materials with attractive performances in analytical and bioanalytical chemistry. The incorporation of biomolecule peptides gives the frameworks conformational flexibility, guest adaptability, built-in chirality, and molecular recognition ability, which greatly accelerate the applications of PMOFs in enantiomeric separation, affinity separation, and the enrichment of bioactive species from complicated samples. This review focuses on the recent advances in the engineering and applications of PMOFs in selective separation. The unique biomimetic size-, enantio-, and affinity-selective performances for separation are discussed along with the chemical structures and functions of MOFs and peptides. Updates of the applications of PMOFs in adaptive separation of small molecules, chiral separation of drug molecules, and affinity isolation of bioactive species are summarized. Finally, the promising future and remaining challenges of PMOFs for selective separation of complex biosamples are discussed.

Neglected Applications of Monolithic Structures: The Beginnings of Planar Chromatography with Mass Spectrometric Detection

Thin layer chromatography (TLC) has been first reported by N. A. Izmailov and M. S. Schreiber in the late 1930s. The liquid mobile phase usually moves in pores of a layer supported by a rigid plate placed vertically in a simple container, e.g., a beaker. The flow is driven by capillary forces in the pores only and no sophisticated instrumentation is required. The individual components of the mixture are separated based on differences in their affinity for the solid stationary and the liquid mobile phases. The typical format of the stationary phase represents a thin layer coated on a glass, aluminium, or plastic plate. The porous sorbents can be silicon dioxide (silica), aluminium oxide (alumina), and cellulose, held together, e.g., with gypsum. The main advantages of TLC are the ease of carrying out the separations, which can also take place in parallel lines on the same plate, simple equipment, stationary phase for single use, static detection, and the possibility of archiving the separation result in a dried layer. However, the typical 100–250 μm thick layers are not well suited for combination of TLC with mass spectrometry (MS). This has led to the commercialization of ultrathin 10 μm thick monolithic silica layers. Unfortunately, their production was soon discontinued. Alternative solutions to that problem originated from the academic environment. In one approach, the layers were formed from nanofibers prepared by electrospinning. Alternatively, the layers were porous monolithic polymers produced by polymerization in situ and a variety of separations of both small and large molecules was demonstrated. The use of MS detection then enabled determination of molecular mass of the compounds in the separated spots. Although preparation of the thin monolithic layers originally appeared straightforward, some unexpected problems had to be solved. This review details issues related to the history of the monolithic TLC and presents approaches leading to well behaving layers suitable for the desired separations.

Submicron Nonporous Silica Particles for Enhanced Separation Performance in pCEC.

Applications of submicron-scale particles are of rising interest in separation science due to their favorable surface-to-volume ratio and their fabrication of highly ordered structures. The uniformly dense packing beds in columns assembled from nanoparticles combined with an electroosmotic flow-driven system has great potential in a highly efficient separation system. Here, we packed capillary columns using a gravity method with synthesized nanoscale C18-SiO2 particles having diameters of 300-900 nm. The separation of small molecules and proteins was evaluated in the packed columns on a pressurized capillary electrochromatography platform. The run-to-run reproducibility regarding retention time and peak area for the PAHs using a column packed with 300 nm C18-SiO2 particles were less than 1.61% and 3.17%, respectively. Our study exhibited a systematic separation analysis of small molecules and proteins based on the columns packed with submicron particles combined with the pressurized capillary electrochromatography (pCEC) platform. This study may provide a promising analytical approach with extraordinary column efficiency, resolution, and speed for the separation of complex samples.

A Bioinspired Capillary Force‐Induced Driving Strategy for Constructing Ultra‐Low‐Pressure Separation Membranes

AbstractThe development of low‐pressure or pressureless self‐driven membranes is important for saving energy and overcoming the critical trade‐off effect in membrane separation processes. However, conventional self‐driven membranes rely on gravity, which is effective in the separation of large‐sized materials but is still ineffective in the fine separation of small molecules. Herein, inspired by the capillary effect that exists in nature, a capillary force‐induced membrane‐driving strategy for fine separation at ultra‐low pressures is demonstrated. Hydrophilic nanoparticles are prepared by a cross‐linking reaction between tannic acid and 3‐aminopropyltriethoxysilane and then introduce them into membrane pores to simulate sand accumulation with an aim to generate the capillary force. The membrane is then used in ultra‐low pressure membrane separation. Interestingly, it is found that the membrane has excellent performance in the separation of dye/salt mixtures (dye rejection > 99%, salt rejection < 10%) and a high permeate flux (160 L m−2 h−1) under near “zero pressure” conditions. Moreover, the structural stability of the membrane is verified. Introducing capillary forces into membranes as an autonomous driving force can be a promising universal approach that can be added up to the toolbox for the efficient preparation of separation membranes.

Highly porous ultrathin polyamide membranes for fast separation of small molecules from organic solvents

Membranes with permselective performance as well as high stability in harsh solvents are urgently desired for energy-efficient precise chemical separations. In this work, we utilize an adamantane diamine as a molecular building block to fabricate thin-film composite polyamide membranes for high-performance organic solvent nanofiltration (OSN). The bulky, cage-like adamantane structure acts as a molecular-level steric hindrance unit to inhibit polymer chain packing which generating interconnected micropores within the interfacially polymerized polyamide layer. This translates into high membrane methanol permeance of 20.6 L m-2 h-1 bar-1 and 94.7% retention to organic dye molecules with molecular weight down to 327 g mol-1. Furthermore, the membrane demonstrates high stability in different organic solvents taking advantage of the crosslinked rigid structure, which shows constant solute retention throughout a 180 h continuous filtration experiment with a DMF solution containing methyl orange as feed solution. Employing rigid and bulky molecular features in selective layer is thus demonstrated to significantly promote the polyamide membrane permeability and solvent resistance without compromising the overall selectivity.

Quantitative Structure Retention-Relationship Modeling: Towards an Innovative General-Purpose Strategy

Reversed-Phase Liquid Chromatography (RPLC) is a common liquid chromatographic mode used for the control of pharmaceutical compounds during their drug life cycle. Nevertheless, determining the optimal chromatographic conditions that enable this separation is time consuming and requires a lot of lab work. Quantitative Structure Retention Relationship models (QSRR) are helpful for doing this job with minimal time and cost expenditures by predicting retention times of known compounds without performing experiments. In the current work, several QSRR models were built and compared for their adequacy in predicting the retention times. The regression models were based on a combination of linear and non-linear algorithms such as Multiple Linear Regression, Support Vector Regression, Least Absolute Shrinkage and Selection Operator, Random Forest, and Gradient Boosted Regression. Models were built for five pH conditions, i.e., at pH 2.7, 3.5, 6.5, and 8.0. In the end, the model predictions were combined using stacking and the performances of all models were compared. The k-nearest neighbor-based application domain filter was established to assess the reliability of the prediction for further compound prioritization. Altogether, this study can be insightful for analytical chemists working with RPLC to begin with the computational prediction modeling such as QSRR to predict the separation of small molecules.

Sample plug induced peak splitting in capillary electrophoresis studied using dual backscattered interferometry and fluorescence detection.

The appearance of unexpected peaks in capillary electrophoresis (CE) is common and can lengthen the time of method development as assay conditions and experimental parameters are varied to understand and mitigate the effects of the additional peaks. Additional peaks can arise when a single-analyte zone is split into multiple zones. Understanding the underlying mechanism of these phenomena, recognizing conditions that favor its presence, and knowing how to confirm and eliminate the effect are important for efficient method optimization. In this study, we examine how the overlap of analyte zones with the sample plug can lead to peak splitting. This is explored experimentally using dual detection CE, which enables both the sample plug and analyte zones to be independently and simultaneously measured from the same detection volume. Simulations performed via COMSOL Multiphysics confirm the origin of the splitting and help guide experiments to reduce and eliminate the effect. Our findings show that this peak splitting mechanism can arise in separations of both small and large molecules but is, especially, prevalent in separations of slowly migrating macromolecules. This effect is also more prevalent when using a short length-to-detector, as is commonly found in microfluidic applications. A simple diffusion-less model is introduced to develop strategies for reducing peak splitting that avoids modifying the apparatus, such as by lengthening the separation length, which can be difficult. Decreasing the sample plug length and slowing the electroosmotic flow can both reduce this effect, which is confirmed experimentally.

Ion Mobility Mass Spectrometry for the Separation and Characterization of Small Molecules.

Ion Mobility Mass Spectrometry for the Separation and Characterization of Small Molecules.

Engineering gas separation property of metal–organic framework membranes via polymer insertion

We report on a novel approach to engineering the gas permeation property of metal–organic framework (MOF) membranes via polymer infiltration. This method enables MOFs of a too large intrinsic aperture size (>0.7 nm) for membrane separation of small molecules. [Zn2(bdc)2ted]n, referred to as ZnMOF, is studied as a model system for the proof of concept. This MOF has a pore limiting diameter of 7.63 Å, which is notably larger than the kinetic diameters of the gases to be separated (2.89, 3.3, and 3.8 Å for H2, CO2, and CH4, respectively). We prepare ZnMOF membranes, followed by the insertion of polyethylene glycol (PEG) via dip coating, spin-on deposition, or drop coating. Comprehensive materials characterization is performed via a number of solid-state techniques, including nitrogen physisorption, Fourier-transform infrared spectroscopy, thermogravimetric analysis, solution-state nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The results suggest that the three deposition methods all enable the infiltration of PEG in the micropores of the ZnMOF membranes. The as-made ZnMOF membrane possesses low gas selectivity (5.19 for H2/CO2 and 3.8 for H2/CH4), owing to its large pore size. With the PEG infiltration, the ZnMOF membrane presents good selectivity of H2/CO2 (26.28) and H2/CH4 (17.6). Molecular simulations also suggest that the impregnation of PEG reduces the effective pore size of the ZnMOF structure and thus renders it a higher diffusion selectivity for gas mixtures as compared to the bare PEG or the pristine ZnMOF membranes.