The silanol group and its role in liquid chromatography

Sensitivity enhancement via multiple contacts in the {1H–29Si}–1H cross polarization experiment: a case study of modified silica nanoparticle surfaces

{¹H–²⁹Si}–¹H double cross polarization inverse detection (DCPi) solid-state NMR, has recently been shown to be a powerful tool for studying molecules adsorbed on the silica surface. In this contribution, we develop an improved version (MCPi) which incorporates a block of multiple contact pulses, and quantitatively compare the sensitivities of MCPi and DCPi over a typical range of experimental parameters. The MCPi pulse sequence aims at higher sensitivity and robustness for studying samples with various relaxation characteristics. In the case of dimethyl sulfoxide (DMSO) molecules adsorbed on the silica surface, MCPi performs equally well or up to 2.5 times better than DCPi over a wide range of parameters. The applicability to and performance of MCPi on composite materials was demonstrated using a sample of polymer–silica composite, where significantly higher sensitivity could be achieved at very long total mixing times. The results also showed that both techniques are surface specific in the sense that only the groups close to the surface can be detected.

In this paper we demonstrate {¹H–²⁹Si}–¹H multiple cross polarization inverse detection (MCPi) solid state NMR as a robust technique for studying modified silica nanoparticle surfaces.

Functionalized Nanoparticles for the Dispersion of Gas Hydrates in Slurry Flow

Gas hydrates are crystals that can form in oil and gas production. Their agglomeration in flowlines may disrupt the normal production. One current strategy of hydrate management is to inject an anti-agglomerant, a type of low-dosage hydrate inhibitor that prevents hydrate agglomeration. Concerns in the use of these chemicals include their toxicity, cost, and environmental impacts. In this study, we exploited functionalized nanoparticles in place of anti-agglomerants to produce hydrate slurry, with the potential benefit of nanoparticles to be more environmentally friendly and conveniently recyclable. We coated 256 nm spherical silica nanoparticles with different hydrophobicity and evaluated their performance for the hydrate dispersion at atmospheric and high pressure. Nanoparticles with moderate hydrophobicity stabilized oil-in-water (O/W) or water-in-oil (W/O) emulsions. Direct visualization of the cyclopentane hydrate formation from the nanoparticle-stabilized emulsions revealed different morphologies of hydrate particles depending on whether the nanoparticles prevented agglomeration. We also measured the apparent viscosity of a hydrate-nanoparticle mixture using a high-pressure rheometer. Nanoparticles with moderate hydrophobicity during hydrate formation slowed the viscosification, reduced the maximum viscosity, increased the water conversion, and ultimately helped to maintain a low steady-state viscosity. Increasing nanoparticle or salt concentrations also improved the gas hydrate dispersion. Our study demonstrated the great potential of using nanoparticles in preventing agglomeration of gas hydrates under realistic pipeline flow conditions.

Estimation of Solute-Stationary Phase and Solute-Mobile Phase Interactions in the Presence of Ionic Liquids

The presence of free silanols on alkyl-bonded reversed-phase stationary phases is responsible for broad and asymmetrical peaks when basic drugs are chromatographed with conventional octadecylsilane (C18) columns due to ionic interactions. In the last few years, ionic liquids (ILs) have attracted attention to reduce this undesirable silanol activity. ILs should be considered as dual modifiers (with a cationic and anionic character), which means that both cations and anions are able to adsorb on the stationary phase, creating a positively or negatively charged layer, depending on the relative adsorption. The accessibility of basic compounds to the silanols is prevented by both the IL cation and anion, improving the peak profiles. A comparative study of the performance of six imidazolium-based ILs, differing in their cation/anions, as modifiers of the chromatographic behavior of a group of ten β-adrenoceptor antagonists, is addressed. Mobile phases containing cationic amines (triethylamine and dimethyloctylamine) were used as a reference for the interpretation of the results. Using a mathematical model based on two chemical equilibria, the association constants between the solutes and modified stationary phase as well as those between solutes and the additive in the mobile phase were estimated. These values, together with the changes in retention and peak shape, were used to obtain conclusions about the retention mechanism, changes in the nature of the chromatographic system, and silanol suppression effect.

Application of Ionic Liquids for the Determination of Lipophilicity Parameters Using TLC Method, and QSRR Analysis for the Antipsychotic Drugs

BACKGROUND

Reversed-phase liquid chromatography may cause difficulties, especially in the case of basic drugs due to the strong silanophilic interactions in the partition mechanism. Recently, imidazolium-based ionic liquids additives appeared interesting and a convenient solution for suppressing the harmful effect of free residuals of silanol groups, allowing remodeling of the stationary/mobile-phase system, and thus improving the lipophilicity assessment process.

OBJECTIVE

The aim of the study was to evaluate the retention behavior of basic antipsychotics using various RP-LC systems, and compare them with data obtained from the modified ionic-liquids RP-TLC systems, and perform the QSRR analysis.

METHODS

Retention and lipophilicity parameters of diverse antipsychotics have been examined in various RP-LC systems. Lipophilicity indices were compared with miscellaneous computed logP values. Furthermore, a large number of molecular descriptors have been computed and compared using various medicinal chemistry software, in order to contribute to the analysis of QSRR.

RESULTS

Designated correlation coefficients showed that lipophilicity parameters from TLC systems without [EMIM][BF4] additive correlates very poor with the calculated logPs indices, whereas the indices from the traditional HPLC and TLC systems (with [EMIM][BF4]) were clearly better. Furthermore, QSRR analysis performed for these experimentally obtained lipophilicity parameters showed significant relationships between the retention constants (R^O_M, log_kw) and the in silico calculated physicochemical molecular descriptors.

CONCLUSION

ILs additive may be a significant factor affecting the lipophilicity of basic compounds, thus their use may be favorable in lipophilicity assessment studies. QSRR models with ILs showed that they may be useful in searching/or predicting HPLC/TLC retention parameters for the new/other antipsychotic drugs.

Column Characterization and Selection Systems in Reversed-Phase High-Performance Liquid Chromatography

Reversed-phase high-performance liquid chromatography (RP-HPLC) is the most popular chromatographic mode, accounting for more than 90% of all separations. HPLC itself owes its immense popularity to it being relatively simple and inexpensive, with the equipment being reliable and easy to operate. Due to extensive automation, it can be run virtually unattended with multiple samples at various separation conditions, even by relatively low-skilled personnel. Currently, there are >600 RP-HPLC columns available to end users for purchase, some of which exhibit very large differences in selectivity and production quality. Often, two similar RP-HPLC columns are not equally suitable for the requisite separation, and to date, there is no universal RP-HPLC column covering a variety of analytes. This forces analytical laboratories to keep a multitude of diverse columns. Therefore, column selection is a crucial segment of RP-HPLC method development, especially since sample complexity is constantly increasing. Rationally choosing an appropriate column is complicated. In addition to the differences in the primary intermolecular interactions with analytes of the dispersive (London) type, individual columns can also exhibit a unique character owing to specific polar, hydrogen bond, and electron pair donor-acceptor interactions. They can also vary depending on the type of packing, amount and type of residual silanols, "end-capping", bonding density of ligands, and pore size, among others. Consequently, the chromatographic performance of RP-HPLC systems is often considerably altered depending on the selected column. Although a wide spectrum of knowledge is available on this important subject, there is still a lack of a comprehensive review for an objective comparison and/or selection of chromatographic columns. We aim for this review to be a comprehensive, authoritative, critical, and easily readable monograph of the most relevant publications regarding column selection and characterization in RP-HPLC covering the past four decades. Future perspectives, which involve the integration of state-of-the-art molecular simulations (molecular dynamics or Monte Carlo) with minimal experiments, aimed at nearly "experiment-free" column selection methodology, are proposed.

Relevance of silica surface morphology in Ampyra adsorption. Insights from quantum chemical calculations

Theoretical calculations are performed using the Vienna Ab-initio simulation package (VASP) to understand the mechanisms that control the adsorption of Ampyra drug on the different crystallographic planes of β-cristobalite: the hydroxylated (111) and (100) surfaces. The Ampyra-silica interaction is most favored on the (100) surface where the entire ring of the molecule interacts with the surface while on the (111) face, lesser exchange and fewer non-polar atoms are involved. Calculations show that the interactions mainly occur at the interface between the Ampyra and the closest silanol groups, according to the formation of the H-bonding interactions. The results indicate that the H-bonds have an important influence on the adsorption of the Ampyra. In consequence, adsorption on the (111) surface is observed to a lesser extent than on the (100) surface according the smaller hydroxyl density.

DFT calculations are performed to understand the mechanisms that control the adsorption of Ampyra drug on the different crystallographic planes of β-cristobalite: the hydroxylated (111) and (100) surfaces.

Characterization of Multimodal Silicas Using TG/DTG/DTA, Q-TG, and DSC Methods

The formation of hierarchical, multimodal porosity materials with controlled shape and size of pores is the essential challenge in materials science. Properties of silica materials depend largely on different features: crystal structure, dispersity, surface composition, and porosity as well as the method of preparation and possible modification. In this paper, multimodal silicas obtained using different additives are presented. A-50 and A-380 aerosils and wide-porous SiO2 milled at 300 rpm were used as the additives in the sol stage at 20 °C, the sol–gel stage followed by hydrothermal modification (HTT) at 200 °C, or in the mechanochemical treatment (MChT) process. The characterizations were made by application of N2 adsorption/desorption, SEM imaging, quasi-isothermal thermogravimetry (Q-TG), dynamic thermogravimetry/derivative thermogravimetry/differential thermal analysis (TG/DTG/DTA), and cryoporometry differential scanning calorimetry (DSC) methods. Results showed that such a one-step preparation method is convenient and makes it possible to obtain multimodal silicas of differentiated porous structures and surface chemistry.

Exploring the Effect of Buffer Strength on the Retention Time of Weak Acids, Neutral and Weak Bases in Hydrophilic Interaction Liquid Chromatography (HILIC) Mode

Background:

Hydrophilic Interaction Liquid Chromatography (HILIC) orthogonal to conventional reversed phase High-Performance Liquid Chromatography (HPLC) mode allowing separation of polar compounds. HILIC has been reported to be an alternative to normal phase liquid chromatography, yet the separation mechanism reported in HILIC is much more complicated than that in normal phase liquid chromatography.

Objective:

To investigate the effect of water layer thickness on silica gel and the amount of ammonium ions present within the buffer on retention mechanism in hydrophilic interaction chromatography.

Methodology:

A test system was designed which used weak acids, neutrals and weak bases as probes with three different strengths (5, 10 and 20 mM) of ammonium acetate, ammonium formate and ammonium propionate as the counter-ions to compete with the test probes with ionised silanol groups and water present in the stationary phase. A Kromasil 60-5SIL column (150 mm×4.6 mm×4 μm, pore size 60Å) was used as the stationary phase to perform the study.

Results:

Retention times were examined for the test probes at 90% acetonitrile (ACN) with 10% of 5, 10 and 20 mM of ammonium acetate, ammonium formate and ammonium propionate. As the buffer strength increases, the thickness of the water layer on the surface of the silica gel increases and also the repulsion between ionized silanol groups and acidic test probes will decrease. On the other hand, such increase in buffer strength will increase the competition between the ammonium ions and basic test probes. In addition, the hydration energy of buffer’s counter ions and hydrophilicity may be important in retention mechanism in HILIC mode.

Conclusion:

At 20 mM buffer strength acidic probes with low log P values retain more due to reduced repulsion by silanol groups, while basic probes retention time will decrease due to increased competition from ammonium counter ions. However, in 5 mM buffer strength basic probes with low logP value will be retained longer, while acidic probes will be eluted earlier due to the repulsion between ionized acids and ionized silanol groups.

Trace Phosphate Improves ZIC-pHILIC Peak Shape, Sensitivity, and Coverage for Untargeted Metabolomics

Existing hydrophilic interaction liquid chromatography (HILIC) methods, considered individually, each exhibit poor chromatographic performance for a substantial fraction of polar metabolites. In addition to limiting metabolome coverage, such deficiencies also complicate automated data processing. Here we show that some of these analytical challenges can be addressed for the ZIC-pHILIC, a zwitterionic stationary phase commonly used in metabolomics, with the addition of trace levels of phosphate. Specifically, micromolar phosphate extended metabolome coverage by hundreds of credentialed features, improved peak shapes, and reduced peak-detection errors during informatic processing. Although the addition of high levels of phosphate (millimolar) as a HILIC mobile phase buffer has been explored previously, such concentrations interfere with mass spectrometric (MS) detection. We show that using phosphate as a trace additive at micromolar concentrations improves analysis by electrospray MS, increasing signal for a diverse set of polar standards. Given the small amount of phosphate needed, comparable chromatographic improvements were also achieved by direct addition of phosphate to the sample during reconstitution. Our results suggest that defects in ZIC-pHILIC performance are predominantly driven by electrostatic interactions, which can be modulated by phosphate. These findings constitute both a methodological improvement for untargeted metabolomics and an advance in our understanding of the mechanisms limiting HILIC coverage.

N-Propyl-N'-2-pyridylurea-modified silica as mixed-mode stationary phase with moderate weak anion exchange capacity and pH-dependent surface charge reversal

Herein, we present a novel silica-based stationary phase modified with N-propyl-N'-2-pyridylurea selector. Due to the weakly basic properties of the pyridine selector and the presence of residual silanols after selector immobilization, a zwitterionic surface with a pI observed at approximately pH 5.5 was measured by electrophoretic light scattering in pH-dependent ζ-potential determinations. The capability of the new N-propyl-N'-2-pyridylurea-modified silica to serve as mixed-mode stationary phase was investigated. For this purpose, it was characterized under RP and HILIC conditions using test mixtures. Subsequent classification of this stationary phase in comparison to in-house and commercial benchmarks was carried by principal component analysis of resultant retention factors from chromatographic tests. The results show a relatively unique mixed-mode character amongst the tested stationary phases. The chromatographic retention characteristics of acidic compounds matched well the ζ-potential determinations. The application of anion-exchange at low pH values (e.g. pH 5) and ion exclusion chromatography at pH 7 for the separation of uridine 5'-mono-, di- and triphosphate demonstrated a pH-dependent umpolung of the stationary phase surface. The combination of these separation principles in a pH gradient from 5 to 7 gave rise to weak anion-exchange selectivity with a charge-inducted elution due to repulsive interactions at higher pH and resulted in a significant faster separation with improved peak shape under mild elution conditions.

IR Spectrum and Structure of Protonated Monosilanol: Dative Bonding between Water and the Silylium Ion

We report the spectroscopic characterization of protonated monosilanol (SiH₃ OH₂⁺ ) isolated in the gas phase, thus providing the first experimental determination of the structure and bonding of a member of the elusive silanol family. The SiH₃ OH₂⁺ ion is generated in a silane/water plasma expansion, and its structure is derived from the IR photodissociation (IRPD) spectrum of its Ar cluster measured in a tandem mass spectrometer. The chemical bonding in SiH₃ OH₂⁺ is analyzed by density functional theory (DFT) calculations, providing detailed insight into the nature of the dative H₃ Si⁺ -OH₂ bond. Comparison with protonated methanol illustrates the differences in bonding between carbon and silicon, which are mainly related to their different electronegativity and the different energy of the vacant valence p_z orbital of SiH₃⁺ and CH₃⁺ .

A review of Fischer Tropsch synthesis process, mechanism, surface chemistry and catalyst formulation

For more than half a century, Fischer-Tropsch synthesis (FTS) of liquid hydrocarbons was a technology of great potential for the indirect liquefaction of solid or gaseous carbon-based energy sources (Coal-To-Liquid (CTL) and Gas-To-Liquid (GTL)) into liquid transportable fuels. In contrast with the past, nowadays transport fuels are mainly produced from crude oil and there is not considerable diversity in their variety. Due to some limitations in the first generation bio-fuels, the Second-Generation Biofuels (SGB)’ technology was developed to perform the Biomass-To-Liquid (BTL) process. The BTL is awell-known multi-step process to convert the carbonaceous feedstock (biomass) into liquid fuels via FTS technology. This paper presents a brief history of FTS technology used to convert coal into liquid hydrocarbons; the significance of bioenergy and SGB are discussed aswell. The paper covers the characteristics of biomass, which is used as feedstock in the BTL process. Different mechanisms in the FTS process to describe carbon monoxide hydrogenation aswell as surface polymerization reaction are discussed widely in this paper. The discussed mechanisms consist of carbide, CO-insertion and the hydroxycarbene mechanism. The surface chemistry of silica support is discussed. Silanol functional groups in silicon chemistry are explained extensively. The catalyst formulation in the Fischer Tropsch (F-T) process as well as F-T reaction engineering is discussed. In addition, the most common catalysts are introduced and the current reactor technologies in the F-T indirect liquefaction process are considered.

3-Dimensional X-ray microtomography methodology for characterization of monolithic stationary phases and columns for capillary liquid chromatography - A tutorial

In this tutorial we describe a fast, nondestructive, three-dimensional (3-D) view approach to be used in morphology characterization of capillary monoliths and columns by reconstruction from X-ray microtomography (XMT) obtained by acquiring projection images of the sample from a number of different directions. The method comprises imaging acquisition, imaging reconstruction using specific algorithms and imaging analysis by generation of a 3-D image of the sample from radiographic images. The 3-D images show the morphological data for bulk macropore space and skeleton connectivity of the monoliths and were compared with other images from imaging techniques such as scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) and with chromatographic performance. The 3-D XMT methodology is applicable for organic and inorganic capillary chromatographic monolithic materials and it allows the acquisition of many hundreds (in our case 1001 projections) of longitudinal and cross-sectional images in a single session, resolving morphological details with a 3D-view of the monolithic structure, inclusive inside the column in a sectional structure with volume (three dimensions) when compared to the sectional structure area (with only two dimensions) when using SEM and FESEM techniques.

RpeakChrom: Novel R package for the automated characterization and optimization of column efficiency in high-performance liquid chromatography analysis

Characterization of chromatographic columns using the traditional van Deemter method is limited by the necessity of calculating extra-column variance, issue particularly relevant when modeling asymmetrical peaks eluted from monolithic columns. A novel R package that implements Parabolic Variance Modified Gaussian approach for accurate peak modeling, van Deemter equation and two alternatives approaches, based on van Deemter, has been developed to calculate the height equivalent to a theoretical plate (HETP). To assess package capabilities conventional packed reverse-phase and monolithic HPLC columns were characterized. Peaks eluted from the monolithic column showed a high value of factor asymmetry due, in part, to the contribution of extra-column factors. Such deviation can be circumvented by the two alternatives approaches implemented in the R-package. Furthermore, increased values of eddy diffusion and mass transfer kinetics terms in HETP were observed for the packed column, while accuracy was below 9% in all cases. These results showed the usefulness of the R-package for both modeling chromatographic peaks and assessing column efficiency. The RpeakChrom package could become a helpful tool for testing new stationary phases during column development and to evaluate column during its lifetime. This R tool is freely available from CRAN (https://CRAN.R-project.org/package=RpeakChrom).

Fragment-based approach to calculate hydrophobicity of anionic and nonionic surfactants derived from chromatographic retention on a C18 stationary phase

To predict the fate and potential effects of organic contaminants, information about their hydrophobicity is required. However, common parameters to describe the hydrophobicity of organic compounds (e.g., octanol-water partition constant [K_OW ]) proved to be inadequate for ionic and nonionic surfactants because of their surface-active properties. As an alternative approach to determine their hydrophobicity, the aim of the present study was therefore to measure the retention of a wide range of surfactants on a C₁₈ stationary phase. Capacity factors in pure water (k'₀ ) increased linearly with increasing number of carbon atoms in the surfactant structure. Fragment contribution values were determined for each structural unit with multilinear regression, and the results were consistent with the expected influence of these fragments on the hydrophobicity of surfactants. Capacity factors of reference compounds and log K_OW values from the literature were used to estimate log K_OW values for surfactants (log KOWHPLC). These log KOWHPLC values were also compared to log K_OW values calculated with 4 computational programs: KOWWIN, Marvin calculator, SPARC, and COSMOThermX. In conclusion, capacity factors from a C₁₈ stationary phase are found to better reflect hydrophobicity of surfactants than their K_OW values. Environ Toxicol Chem 2017;36:329-336. © 2016 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.

UiO-66@SiO2 core–shell microparticles as stationary phases for the separation of small organic molecules

Microparticles decorated with metal–organic frameworks exhibited a unique flow-dependent separation selectivity (FDSS) effect for the isocratic separation of small molecules.

Separation behavior of basic compounds on unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases with reversed-phase eluents

Unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases have been evaluated and compared for the separation of basic compounds of differing molecular weight, pK_a , and log D using aqueous/organic mobile phases. The influences of percentage of organic modifier, buffer pH, and concentration in the mobile phase on base retention were investigated on unbonded silicon oxynitride and silica phases. The results confirmed that unbonded silicon oxynitride and silica phases demonstrated excellent separation performance for model basic compounds and both the unbonded phases examined possessed a hydrophobic/adsorption and ion-exchange character. The silicon oxynitride stationary phase exhibited high hydrophilicity compared with silica with a reversed-phase mobile phase. An ion-exclusion-type mechanism becomes predominant for the separation of three aimed bases on the silicon oxynitride column at pH 2.8. Different from silicon oxynitride stationary phase, no obvious change for the retention time of three model bases on silica stationary phase at pH 2.8 can be observed.

Phenol and methylene blue photodegradation over Ti/SBA-15 materials under uv light

Ordered SBA-15 mesoporous silica supports have been synthesized and used for incorporation of titanium with different Ti/Si weight ratio via incipient wetness impregnation. Titanium tetraisopropoxide (TTIP) was used as a source of Ti. Obtained catalysts were characterized to investigate the chemical framework and morphology by nitrogen sorption measurements, powder X-ray diffraction (XRD), X-ray fluorescence elemental analysis (XRF), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS). The photocatalytic degradation of phenol and methylene blue water solutions were selected as a probe reactions to the photoactivity test of prepared samples and to verify the potential application of these materials for water purification. Experimental results indicate that the photocatalytic activity of Ti/Si mixed materials depends on the adsorption ability of composites and the photocatalytic activity of the titanium oxide.

Probing Heterogeneity and Bonding at Silica Surfaces through Single-Molecule Investigation of Base-Mediated Linkage Failure

The nature of silica surfaces is relevant to many chemical systems, including heterogeneous catalysis and chromatographies utilizing functionalized-silica stationary phases. Surface linkages must be robust to achieve wide and reliable applicability. However, silyl ether-silica support linkages are known to be susceptible to detachment when exposed to basic conditions. We use single-molecule spectroscopy to examine the rate of surface linkage failure upon exposure to base at a variety of deposition conditions. Kinetic analysis elucidates the role of thermal annealing and addition of blocking layers in increasing stability. Critically, it was found that successful surface modification strategies alter the rate at which base molecules approach the silica surface as opposed to reducing surface linkage reactivity. Our results also demonstrate that the innate structural diversity of the silica surface is likely the cause of observed heterogeneity in surface-linkage disruption kinetics.

Performance of amines as silanol suppressors in reversed-phase liquid chromatography

In reversed-phase liquid chromatography, cationic basic compounds yield broad and asymmetrical peaks, as a result of their ionic interaction with the anionic free silanol groups present in the silica-based stationary phases (commonly derivatised with C18 groups). A simple way to improve the peak shape is the addition to the hydro-organic mobile phase of a reagent (usually called additive) with cationic character. This associates with the stationary phase to prevent the access of analytes to the free silanol groups. Cationic additives may interact electrostatically with the anionic silanols. The hydrophobic region of the additive may also associate with the alkyl chains bound to the stationary phase, with the positive charge oriented towards the mobile phase. The access to the silanol groups is thus blocked, but in turn, the stationary phase is positively charged and will repel the protonated basic compounds, which unless their polarity is sufficiently low, will elute at very short times. In this work, a comparative study of the performance of a group of amines (butylamine, pentylamine, hexylamine, cyclopentylamine, cycloheptylamine, N,N-dimethyloctylamine and tributylmethylammonium chloride), as modifiers of the chromatographic behaviour of basic compounds, is carried out. The behaviour is compared with that obtained with the ionic liquids 1-butyl-3-methylimidazolium chloride and 1-hexyl-3-methylimidazolium chloride, used as additives. The study revealed that the performance of the cationic additives to block the silanol activity is mainly explained by the additive size and its ability to be adsorbed onto the stationary phase.

Dipeptide-bonded stationary phases for hydrophilic interaction liquid chromatography

Dipeptide-silica stationary phases were prepared and applied for the analysis of nucleic bases and nucleosides in HILIC mode.

Adsorption and desorption of DNA tuned by hydroxyl groups in graphite oxides-based solid extraction material

The extraction of DNA is the most crucial method used in molecular biology. Up to date silica matrices has been widely applied as solid support for selective DNA adsorption and extraction. However, since adsorption force of SiOH functional groups is much greater than that of desorption force, the DNA extraction efficiency of silica surfaces is limited. In order to increase the DNA extraction yield, a new surface with different functional groups which possess of greater desorption property is required. In this study, we proposed cellulose/graphite oxide (GO) composite as an alternative material for DNA adsorption and extraction. GO/Cellulose composite provides the major adsorption and desorption of DNA by COH, which belongs to alkyl or phenol type of OH functional group. Compared to SiOH, COH is less polarized and reactive, therefore the composite might provide a higher desorption of DNA during the elution process. The GO/cellulose composite were prepared in spherical structure by mixing urea, cellulose, NaOH, Graphite oxide and water. The concentration of GO within the composites were controlled to be 0-4.15 wt.%. The extraction yield of DNA increased with increasing weight percentage of GO. The highest yield was achieved at 4.15 wt.% GO, where the extraction efficiency was reported as 660.4 ng/μl when applying 2M GuHCl as the binding buffer. The absorbance ratios between 260 nm and 280 nm (A260/A280) of the DNA elution was demonstrated as 1.86, indicating the extracted DNA consisted of high purity. The results proved that GO/cellulose composite provides a simple method for selective DNA extraction with high extraction efficiency of pure DNA.

Ion-exchange vs reversed-phase chromatography for separation and determination of basic psychotropic drugs

Ion exchange chromatography, an alternative to reversed-phase (RP) chromatography, is described in this paper. We aimed to obtain optimal conditions for the separation of basic drugs because silica-based RP stationary phases show silanol effect and make the analysis of basic analytes hardly possible. The retention, separation selectivity, symmetry of peaks and system efficiency were examined in different eluent systems containing different types of buffers at acidic pH and with the addition of organic modifiers: methanol and acetonitrile. The obtained results reveal a large influence of the salt cation used for buffer preparation and the type of organic modifier on the retention behavior of the analytes. These results were also compared with those obtained on an XBridge C18 column. The obtained results demonstrated that SCX stationary phases can be successfully used as alternatives to C18 stationary phases in the separation of basic compounds. The most selective and efficient chromatographic systems were applied for the quantification of some psychotropic drugs in fortified human serum samples.

Exploration and exploitation of water in colloidal crystals

Water on solid surfaces is ubiquitously found in nature, in most cases due to mere adsorption from ambient moisture. Because porous structures have large surfaces, water may significantly affect their characteristics. This is particularly obvious in systems formed by separate particles, whose interactions are strongly influenced by small amounts of liquid. Water/solid phenomena, like adsorption, condensation, capillary forces, or interparticle cohesion, have typically been studied at relatively large scales down to the microscale, like in wet granular media. However, much less is known about how water is confined and acts at the nanoscale, for example, in the interstices of divided systems, something of utmost importance in many areas of materials science nowadays. With novel approaches, in-depth investigations as to where and how water is placed in the nanometer-sized pores of self-assembled colloidal crystals have been made, which are employed as a well-defined, versatile model system with useful optical properties. In this Progress Report, knowledge gained in the last few years about water distribution in such nanoconfinements is gathered, along with how it can be controlled and the consequences it brings about to extract new or enhance existing material functionalities. New methods developed and new capabilities of standard techniques are described, and the water interplay with the optical, chemical, and mechanical properties of the ensemble are discussed. Some lines for applicability are also highlighted and aspects to be addressed in the near future are critically summarized.