Properties Of Stationary Phases Research Articles

Positive Synergy between the Helical Poly(phenylacetylene) Backbones and the Helical L-Proline Oligopeptide Pendants for Enhanced Enantioseparation Properties.

A series of optically active helical poly(phenylacetylene)s (PPA-Pro1, PPA-Pro3, PPA-Pro6, PPA-Pro9, and PPA-Pro12) bearing different chain lengths of L-proline oligopeptide in the side chains were obtained by polymerizing the corresponding novel phenylacetylene monomers. The monomer adopted a trans-rich helix structure when the L-proline oligopeptide chain length was longer, according to the optical activities and 2D-NMR analysis. The helical structure could be maintained and significantly influenced the polymers' helical conformation by introducing the L-proline oligopeptide to the pendants. By the way, the morphology of PPA-Pro3 was observed by atomic force microscope (AFM) on highly oriented pyrolytic graphite (HOPG), and the information on the helix direction, pitch, and chain arrangement was obtained. Also, the chiral separation properties of these polymer-based chiral stationary phases (CSPs) were investigated using high-performance liquid chromatography (HPLC). The poly(phenylacetylene)s showed enhanced enantioseparation properties toward various racemates depending on the longer chain length of the L-proline oligopeptide in the pendants and the positive synergy between the helical backbone and helical side chains. Particularly, PPA-Pro9 showed comparable or even superior enantioseparation properties for racemates 2 and 9 to four commercial columns (Daicel Chiralpak or Chiralcel AD, AS, OD, and OT), indicating that these poly(phenylacetylene)-based CSPs have potential practical values. This work presented here provides inspiration for the further development of CSPs based on a new paradigm.

Comparison of Chromatographic Stationary Phases Using a Bayesian-Based Multilevel Model.

Herein, we used a Bayesian multilevel model of chromatographic retention to compare five reversed-phase high-performance liquid chromatography stationary phases: XBridge Shield RP18, XTerra MS C18, XBridge Phenyl, XBridge C8, and Xterra MS C8. For this, we used a large data set of retention times collected using chromatographic techniques coupled with mass spectrometry. The experiments were conducted in gradient mode for an initial mixture of 300 small analytes for a wide range of pH values in methanol and acetonitrile at two temperatures and for three gradient durations. Our analysis was based on a mechanistic model derived from the principles and fundamentals of liquid chromatography and utilized previously reported chromatographic parameters. The data and model were used to characterize the between-column differences in the chromatographic parameters of the neutral, acidic, and basic analytes. The analysis provides an interpretable summary of stationary-phase properties that can be used in decision-making, i.e., finding the best chromatographic conditions using limited experimental data. The proposed approach is an interesting alternative to the existing approaches used to compare chromatographic stationary phases.

Virtual chiral recognition of eugenol derivatives on amylose tris(3-chloro-5-methylphenylcarbamate) chiral stationary phase in unusual normal-phase mode

Chromatographic enantioseparation on polysaccharide-based chiral stationary phases has undergone explosive development over the last three decades as a method for separating the enantiomers of chiral compounds on an analytical and preparative scale. In this context, understanding the nature of the intermolecular interactions involved in retention and recognition processes is an interesting scientific challenge. In the present study, three eugenol derivatives were used as chiral references to elucidate some unexplored aspects of the enantioselective and retention properties of the Chiralpak IG-U chiral stationary phase based on amylose-tris(3-chloro-5-methylphenylcarbamate).The performance of the ultra-high performance liquid chromatography chiral packing material Chiralpak IG-U was evaluated using a two-step approach. First, binary mixtures containing variable proportions of alcohol (ethanol or 2-propanol) in n-hexane were used as mobile phases and the retention factors were recorded at three different temperatures. A rational analysis of this set of chromatographic data shows the leading role played by hydrogen bond between the OH group linked to the stereogenic centre of the analytes and the active sites of the chiral chromatographic material in obtaining a high degree of enantioseparation.The retention factors were then plotted against the percentage of alcohol modifiers to obtain retention maps with a non-linear performance trend with correlation factors >0.9990.The proposed retention map model was used to extrapolate and describe virtual chiral recognition of chiral analytes on the Chiralpak IG-U chiral stationary phase under extreme elution conditions with expected run times of hundreds or thousands of years. The presented virtual chiral recognition approach is based on a generic concept and therefore opens new possibilities for understanding the performance of other polysaccharide-based chiral stationary phases.

Insights into the Shape-Selective Retention Properties of Porous Graphitic Carbon Stationary Phases and Applicability for Polar Compounds

In this article, the ability of porous graphitic carbon (PGC) to discriminate between structurally similar compounds is described. After a brief overview of the particle technology and its use in liquid chromatography (LC), two case studies are presented using small-molecule probes to illustrate the importance on how molecular shape and the ability to interact with the graphitic surface lead to the resolution of structural isomers. Finally, an application of this technology in the area of glycan analysis is showcased where released N-glycans from human immunoglobulin G (IgG) were resolved without derivatization, enabling the glycan profile of a biotherapeutic to be determined.

Factors affecting mixed-mode retention properties of cation-exchange stationary phases

Cation-exchange stationary phases were characterized in different chromatographic modes (HILIC, RPLC, IC) and applied to the separation of non-charged hydrophobic and hydrophilic analytes. The set of columns under investigation included both commercially available cation-exchangers and self-prepared PS/DVB-based columns, the latter consisting of adjustable amounts of carboxylic and sulfonic acid functional groups. The influence of cation-exchange site and polymer substrate on the multimodal properties of cation-exchangers was identified using selectivity parameters, polymer imaging and excess adsorption isotherms. Introducing weakly acidic cation-exchange functional groups to the unmodified PS/DVB-substrate effectively reduced hydrophobic interactions, whilst a low degree of sulfonation (0.09 to 0.27% w/w sulphur) mainly influenced electrostatic interactions. Silica substrate was found to be another important factor for inducing hydrophilic interactions. The presented results demonstrate that cation-exchange resins are suitable for mixed-mode applications and offer versatile selectivity.

Preparation of three regioisomeric ionic liquid stationary phases and investigation of their retention behavior

The structural properties of ionic liquid stationary phases have a considerable effect on their separation selectivity. However, the difference of the chromatographic retention behavior of different regioisomeric ionic liquid stationary phases has rarely been investigated. In this study, three regioisomeric ionic liquid silane reagents were prepared by photoinitiated ene-click chemistry and bonded to silica by one-pot method to fabricate three new stationary phases (Sil-C2Im-C8, Sil-C6Im-C4, and Sil-C9Im-C1). All three stationary phases showed promising retention repeatability and efficiency. The retention behavior of the three stationary phases was investigated under various chromatographic conditions. The retention mechanism was further investigated by the linear energy solvation relationship and Van't Hoff plots. The stationary phases exhibited mixed-mode retention mechanisms. The π–π, hydrogen bonding, ion-exchange, and hydrophilic interactions with analytes were the weakest when the imidazole ions were embedded in the innermost part of the alkyl chains, while the interactions were the strongest when the imidazole ions were embedded in the middle of the alkyl chains. The three stationary phases provided great but different separation performances towards nucleosides, nucleobases, aromatic acids, alkyl benzenes, and polycyclic aromatic hydrocarbons due to the influence of imidazole ion position.

Impact of the Polymer Backbone Structure on the Separation Properties of New Stationary Phases Based on Tricyclononenes

The main purpose of this paper is to compare the chromatographic properties of capillary columns prepared with polymers with different backbone structures and to demonstrate the possibility of polymer differentiation via inverse gas chromatography. With the use of addition and metathesis types of polymerization of tricyclononenes, two new stationary phases were prepared. The metathesis polymer contained double bonds in the polymeric backbone while the backbone of the addition polymer was fully saturated and relatively mobile. A comparison of the separation and adsorption properties of new phases with conventional gas chromatography (GC) stationary phases clearly indicated their non-polar characteristics. However, the difference in the polymer structure appeared to have very little effect on the stationary phase separation properties, so other parameters were used for polymer characterization. The thermodynamic parameters of the sorption of alkanes and aromatic compounds in both polymeric stationary phases were also very similar; however, the entropy of sorption for hydrocarbons with seven or more carbon atoms was different for the two polymers. An evaluation of the specific surface energy of the stationary phases also allowed us to discriminate the two stationary phases.

Effect of phenyl numbers in polyphenyl ligand on retention properties of aromatic stationary phases

Aromatic phase, as one type of reversed-phase stationary phases, shows complementary selectivity to the n-alkyl counterparts especially for certain challenging separation tasks. However, effect of phenyl numbers in aromatic ligands on retention behaviors has rarely been addressed compared with the alkyl stationary phases. To illustrate the issue, a series of polyphenyl stationary phases were facially prepared via the coupling chemistry of isocyanate with amine, including aniline (π1), 4-aminobiphenyl (π2), 4-amino-p-terphenyl (π3) and [1,1′:4′,1′':4′',1′''-quaterphenyl]-4-amine (π4), respectively. The chromatographic behaviors of the new stationary phases as well as the traditional C18 were systematically compared in terms of retention mode, hydrophobic and aromatic selectivity, shape selectivity and π-π interaction by various analytes, including alkylbenzenes, polycyclic aromatic hydrocarbons congeners and substituted benzenes with electron-withdrawing groups. Due to the homologous structure of four polyphenyl ligands, the hydrophobic selectivity, aromatic selectivity and shape selectivity of stationary phases increase with phenyl numbers in the bonded polyphenyl ligands, whereas the increment becomes insignificant from U-π3 to U-π4. This phenomenon is explained by the insertion degree of analytes in the polyphenyl ligand brushes. Compared with the homemade C18, the polyphenyl phases indicate insignificant changes of shape selectivity with temperature. Notably, the new polyphenyl phases demonstrate the great selective separation towards the electron-deficient compounds through the π-π interaction. These findings make up for the understanding of the retention behavior of aromatic stationary phases.

Automated ion exchange chromatography screening combined with in silico multifactorial simulation for efficient method development and purification of biopharmaceutical targets.

Bioprocess development of increasingly challenging therapeutics and vaccines requires a commensurate level of analytical innovation to deliver critical assays across functional areas. Chromatography hyphenated to numerous choices of detection has undeniably been the preferred analytical tool in the pharmaceutical industry for decades to analyze and isolate targets (e.g., APIs, intermediates, and byproducts) from multicomponent mixtures. Among many techniques, ion exchange chromatography (IEX) is widely used for the analysis and purification of biopharmaceuticals due to its unique selectivity that delivers distinctive chromatographic profiles compared to other separation modes (e.g., RPLC, HILIC, and SFC) without denaturing protein targets upon isolation process. However, IEX method development is still considered one of the most challenging and laborious approaches due to the many variables involved such as elution mechanism (via salt, pH, or salt-mediated-pH gradients), stationary phase's properties (positively or negatively charged; strong or weak ion exchanger), buffer type and ionic strength as well as pH choices. Herein, we introduce a new framework consisting of a multicolumn IEX screening in conjunction with computer-assisted simulation for efficient method development and purification of biopharmaceuticals. The screening component integrates a total of 12 different columns and 24 mobile phases that are sequentially operated in a straightforward automated fashion for both cation and anion exchange modes (CEX and AEX, respectively). Optimal and robust operating conditions are achieved via computer-assisted simulation using readily available software (ACD Laboratories/LC Simulator), showcasing differences between experimental and simulated retention times of less than 0.5%. In addition, automated fraction collection is also incorporated into this framework, illustrating the practicality and ease of use in the context of separation, analysis, and purification of nucleotides, peptides, and proteins. Finally, we provide examples of the use of this IEX screening as a framework to identify efficient first dimension (1D) conditions that are combined with MS-friendly RPLC conditions in the second dimension (2D) for two-dimensional liquid chromatography experiments enabling purity analysis and identification of pharmaceutical targets.

Practical and theoretical considerations of the effects of ionic liquids on the separation properties of phenyl-based stationary phases in reversed-phase liquid chromatography

The use of ionic liquids (ILs) as mobile phase additives in reversed-phase liquid chromatography (RP-LC) can influence the dynamic coating of the stationary phases and even allow them to change their chromatographic properties. In this study, the interaction between thirteen different ILs added to 0.1% HCOOH (mobile phase) and the functional groups on phenyl and pentafluorophenyl stationary phases was investigated via RP-LC analysis and the fluorescence detection (FL) of four basic aromatic analytes (anthracycline antibiotics). In addition, an octadecyl column was included in the experiments to investigate potential differences in how the aromatic and alkyl stationary phases interacted with the tested ILs. Changes in behaviors of the studied analytes in the absence and presence of tested ILs were evaluated based on retention factor (k), peak area (A), number of theoretical plates (NA) and tailing factor (Tf). Furthermore, hierarchical cluster analysis (HCA) and k-means approach were used to better visualize found relationships between the chromatographic parameters of anthracyclines for each column. The obtained results indicated that π-π interactions occurring on the phenyl-based stationary phases resulted in more pronounced effects from the ILs compared to those occurring on the alkyl stationary phase. Different subclusters of the k, A, NA, and Tf parameters detected by the HCA confirmed that the addition of ILs leads to various changes in the chromatographic parameters of the studied analytes. These observations were additionally confirmed by k-means calculations. Overall, our findings show that selecting the appropriate IL for addition to the mobile phase can significantly reduce analysis time and improve peak shape and column performance when using aromatic stationary phases.

Supercritical fluid chromatography for the analysis of natural dyes: From carotenoids to flavonoids.

Plant-derived natural dyes are used in a variety of formulated products, from food to cosmetics and pharmaceutics. In addition to their color, they also provide some bioactivity. While they are mostly analyzed with high-performance liquid chromatography, supercritical fluid chromatography was also employed for several dye families, mostly for carotenoids and chlorophylls, and more recently for anthraquinones and flavonoids. These supercritical fluid chromatography methods are described in this review. Because the dyes have different structures and structural variations (polarity, isomers, etc.), the best chromatographic system to achieve their separation is not always the same. Hydrophobic stationary phases are preferred for the most hydrophobic dyes (chlorophylls and carotenoids) while polar stationary phases are preferred for the polar dyes (anthraquinones and flavonoids). Regarding the mobile phase composition, chlorophylls and carotenoids are best eluted with moderate proportions of co-solvent in CO2 (about 40%), while the most polar glycosylated flavonoids require higher proportions of co-solvent and acidic additives. Because dyes are colorful, ultraviolet-visible detection is often sufficient, while mass spectrometry offers additional structural information. Furthermore, fundamental information can also be gained through chromatographic analysis of dyes: either solubility in supercritical fluids, in view of their extraction, or retention behavior providing an understanding of stationary phase properties.

Overloading behavior of fenoprofen and naproxen as two model compounds on a non-porous silicon pillar array column

In this study, the adsorption behavior of naproxen and fenoprofen as two model compounds on a non-porous pillar array column (NPAC) was investigated under reverse phase liquid chromatography conditions. Band profiles of both analytes were recorded in overloaded concentrations using 30% methanol/water (v/v) as the mobile phase. Breakthrough experiments under the same chromatographic condition were carried out to measure the adsorption isotherms. Single-component adsorption isotherm data were acquired by frontal analysis for each analyte. The isotherms were found to be concave upward and downward for naproxen and fenoprofen, respectively. To find the best agreement between the experimental data points and the adsorption isotherm models, the obtained isotherms were modeled using several isotherm models. The Langmuir-Freundlich and anti-Langmuir models provided the best fitting for fenoprofen and naproxen, respectively. The solute and stationary phase properties determine the appropriate model. Adsorbate–adsorbate interaction is important in the case of naproxen, while the adsorbate- adsorbent (stationary phase) plays the main role in retention of fenoprofen on the NPAC. The validity of the selected isotherm models were checked by comparing calculated and experimental band profiles and plate heights. An excellent agreement was observed for the whole concentration range of both analytes, which confirmed the accuracy of the selected models.

Mixed-mode hydrophilic interaction/ion-exchange liquid chromatography – Separation potential in peptide analysis

In this work, three recently developed HILIC columns, i.e., HILIC-A containing silica gel, HILIC-N containing polyhydroxy phase and HILIC-B containing aminopropyl, were characterized in detail to compare their peptide retention, selectivity, and peak symmetry. The detailed study of chromatographic behavior of peptides revealed that a multimodal retention mechanism is present in systems with these stationary phases. Using three model analytes (caffeine, benzenesulfonic acid, and benzyltrimethylammonium chloride), we demonstrated that the HILIC-A column behaves as a HILIC/cation exchanger, and the HILIC-B column as a HILIC/anion exchanger depending on the mobile phase pH and buffer concentration. Furthermore, the pH (ammonium formate, pH 2.1 and 3.5; ammonium acetate pH 5.5) and buffer concentration (10–50 mM) of the mobile phase affect peptide retention and peak symmetry. Satisfactory retention and peak shape of peptides can be obtained by balancing ionic and hydrophilic properties of both analyte and stationary phases. Therefore, buffer concentration and pH optimization is an effective tool for manipulating retention and peak symmetry, thereby enhancing the potential of these columns in the analysis of diverse compounds. The potential application of these columns in the separation of biologically active peptides was confirmed by achieving baseline separation under optimized gradient elution.

Aggregation-Fragmentation of Clusters in the Framework of gTASEP with Attraction Interaction

This article provides summary of some of our results, concerning a model of aggregation and fragmentation of clusters of particles obeying the stochastic discrete-time discrete-space kinetics of the generalized Totally Asymmetric Simple Exclusion Process (gTASEP) with open boundaries. The model in essence is the ordinary TASEP with backward ordered sequential update with special kinematic interaction added, i.e., it has a second modified hopping probability $$~{{p}_{m}}$$ for particles in a cluster in addition to the standard hopping probability $$p$$ . We consider separately the two cases of attraction interaction ( $$p$$ < $$~{{p}_{m}}$$ ): (1) the limiting case of irreversible aggregation ( $${{p}_{m}}$$ = 1); and (2) the generic case of attraction, when $$~p$$ < $$~{{p}_{m}}$$ < 1 (then aggregation and fragmentation of clusters is allowed). We put special emphasis on the use of random walk theory in the study of gTASEP. It is applied to study the inter-cluster gaps time evolution, which helps to assess the properties of the nonequilibrium stationary phases of the system and the phase transitions between them. Theoretical conclusions are in agreement with the Monte Carlo simulations.

Surface properties of stationary phases with embedded polar group based on secondary interaction, zeta potential measurement and linear solvatation energy relationship studies

The chromatographic properties of six non-commercially available stationary phases with ester or phosphodiester functional groups embedded into alkyl chain were studied. Zeta potential values of stationary phases suspended in water, organic solvent and their mixtures were measured. Moreover, the selectivity coefficients were calculated on the basis of the retention factor for the test solutes. Separations were performed under hydrophilic interaction liquid chromatographic conditions. Hydrophobic and polar properties of the investigated columns were compared. Based on the chromatographic properties, polar embedded packing materials were classified. Also two phases with different spacer but the same embedded polar group and alkyl chain (Amino-P-C18 and Diol-P-C18) were used for comparison with homemade materials. Amino-P-C18 stationary phase exhibits positive values of zeta potential which is in accordance with the observed anion exchange properties. The highest negative values of zeta potential were observed for Diol-P-C18, together with cation exchange properties. The highest methylene selectivity, polar selectivity and configurational selectivity were observed for the stationary phase with an ester bond and a phenyl group.

The effect of particle and ligand types on retention and peak shape in liquid chromatography

A well performed, detailed characterization of stationary phase properties can serve as a useful tool for choice of suitable separation environment for a given purpose. This work shows effects of particle type/technology and ligand chemistry on retention and peak shape of neutral, acidic, basic and zwitterionic compounds. Eight columns differing in endcapping technology, particle type and ligand bonded were evaluated, namely XSelect CSH C18, XSelect CSH Phenyl-Hexyl, XSelect CSH Fluoro-Phenyl, XSelect HSS C18, XSelect HSS C18 SB, XSelect HSS PFP, XBridge C18 and XBridge Shield RP18. A simple Walters test for evaluation of hydrophobicity and silanol activity was performed. Mobile phases composed of acetonitrile and aqueous part (pH 2.1; pH 4.7 and pH 8.0) were used. More detailed description of interactions participating in the retention mechanism was provided by the linear free energy relationship model. For a more detailed characterization of possible electrostatic interactions, compounds with permanent charge across selected pH range were used. A good agreement between the Walters test results, the expanded linear free energy relationship model, and the test of ionic-interactions was observed, suggesting that each testing method provides value for characterization of the solute-stationary phase interactions.

Comparison of Various Chromatographic Systems for Identification of Vortioxetine in Bulk Drug Substance, Human Serum, Saliva, and Urine Samples by HPLC-DAD and LC-QTOF-MS.

Background: Determination of psychotropic drugs in clinical study is significant, and the establishment of methodologies for these drugs in biological matrices is essential for patients’ safety. The search for new methods for their detection is one of the most important challenges of modern scientific research. The methods for analyzing of psychotropic drugs and their metabolites in different biological samples should be based on combining a very efficient separation technique including high-performance liquid chromatography (HPLC), with a sensitive detection method and effectively sample preparation methods. Objective: Retention, peaks symmetry and system efficiency of vortioxetine on Hydro RP, Polar RP, HILIC A (with silica stationary phase), HILIC-B (with aminopropyl stationary phase), and ACE HILIC-N (with polyhydroxy stationary phase and SCX columns were investigated. Various mobile phases containing methanol or acetonitrile as organic modifiers and different additives were also applied to obtained optimal retention, peaks shape, and systems efficiency. The best chromatographic procedure was used for simultaneous analysis of vortioxetine and its metabolites in human serum, urine and saliva samples. Methods: Analysis of vortioxetine was performed in various chromatographic systems: Reversed phase (RP) systems on alkylbonded or phenyl stationary phases, hydrophilic interaction liquid chromatography (HILIC), and ion-exchange chromatography (IEC). Based on the dependence of log k vs the concentration of the organic modifier, log kw values for vortioxetine in various chromatographic systems were determined and compared with calculated log P values. Solid phase extraction (SPE) method was applied for sample pre-treatment before HPLC analysis. HPLC-QTOF-MS method was applied for confirmation of presence of vortioxetine and some its metabolites in biological samples collected from psychiatric patient. Conclusions: Differences were observed in retention parameters with a change of the applied chromatographic system. The various properties of stationary phases resulted in differences in vortioxetine retention, systems’ efficiency, and peaks’ shape. Lipophilicity parameters were also determined using different HPLC conditions. The most optimal systems were chosen for the analysis of vortioxetine in biological samples. Both serum and urine or saliva samples collected from patients treated with vortioxetine can be used for the drug determination. For the first time, vortioxetine was detected in patient’s saliva. Obtained results indicate on possibility of application of saliva samples, which collection are non-invasive and painless, for determination and therapeutic drug monitoring in patients.

Performance comparison of nonlinear and linear regression algorithms coupled with different attribute selection methods for quantitative structure - retention relationships modelling in micellar liquid chromatography

In micellar liquid chromatography (MLC), the addition of a surfactant to the mobile phase in excess is accompanied by an alteration of its solubilising capacity and a change in the stationary phase's properties. As an implication, the prediction of the analytes’ retention in MLC mode becomes a challenging task. Mixed Quantitative Structure – Retention Relationships (QSRR) modelling represents a powerful tool for estimating the analytes’ retention.This study compares 48 successfully developed mixed QSRR models with respect to their ability to predict retention of aripiprazole and its five impurities from molecular structures and factors that describe the Brij - acetonitrile system. The development of the models was based on an automatic combining of six attribute (feature) selection methods with eight predictive algorithms and the optimization of hyper-parameters. The feature selection methods included Principal Component Analysis (PCA), Non-negative Matrix Factorization (NMF), ReliefF, Multiple Linear Regression (MLR), Mutual Info and F-Regression. The series of investigated predictive algorithms comprised Linear Regressions (LR), Ridge Regression, Lasso Regression, Artificial Neural Networks (ANN), Support Vector Regression (SVR), Random Forest (RF), Gradient Boosted Trees (GBT) and K-Nearest neighbourhood (k-NN).A sufficient amount of data for building the model (78 cases in total) was provided by conducting 13 experiments for each of the 6 analytes and collecting the target responses afterwards. Different experimental settings were established by varying the values of the concentration of Brij L23, pH of the aqueous phase and acetonitrile content in the mobile phase according to the Box-Behnken design. In addition to the chromatographic parameters, the pool of independent variables was expanded by 27 molecular descriptors from all major groups (physicochemical, quantum chemical, topological and spatial structural descriptors). The best model was chosen by taking into consideration the Root Mean Square Error (RMSE) and cross-validation (CV) correlation coefficient (Q2) values.Interestingly, the comparative analysis indicated that a change in the set of input variables had a minor impact on the performance of the final models. On the other hand, different regression algorithms showed great diversity in the ability to learn patterns conserved in the data. In this regard, testing many regression algorithms is necessary in order to find the most suitable technique for model building. In the specific case, GBT-based models have demonstrated the best ability to predict the retention factor in the MLC mode. Steric factors and dipole-dipole interactions have proven to be relevant to the observed retention behaviour. This study, although being of a smaller scale, is a most promising starting point for comprehensive MLC retention prediction.

Preparation and chromatographic properties of mixed-mode chromatographic stationary phases modified by imidazole side-group functionalized poly(ionic liquids)

A novel mixed-mode chromatographic stationary phase was prepared via surface initiated atom transfer radical polymerization using an imidazole side-group functionalized ionic liquid monomer, 1-(4-vinylbenzyl)-3-cyanomethyl bromide. The structure of the stationary phase was characterized by infrared spectroscopy, elemental analysis, and thermogravimetric analysis. The stationary phase showed good separation ability. The retention mechanism of reversed-phase/ion exchange toward solutes on the stationary phase was verified by determining the effect of mobile phase pH on the retention of substances. Compared with octadecylsilyl-bonded silica stationary phase, it is confirmed that the poly(ionic liquid)-modified stationary phase provides π-π interaction toward the retention of the solutes. The results show that the functionalization of imidazole side groups is a feasible method for preparing new ionic liquid stationary phases.

Diffraction velocity analysis in a single-channel seismic survey in the Joetsu Basin

Historically, marine research has been using single-channel seismic (SCS) devices for scientific projects. Despite SCS’s abundant data availability and the contribution it has brought for subsurface comprehension, few efforts have been dedicated to improve the SCS processing flow to extract more information carried by seismic signals and for better imaging. Diffractions present the necessary means to estimate sediment acoustic properties useful for imaging, stability studies, and geohazard prevention. The root-mean-square (rms) velocity is estimated from diffractions using a diffraction velocity analysis workflow composed of the following main steps: separation of diffractions from specular events using stationary phase properties and plane-wave destruction filtering, determination of diffractor locations in time, velocity scanning using constant rms velocity time migration, automatic picking of rms velocity at the diffractor location in the scan volume, and quality control to avoid spurious rms velocity. The method circumvents the sparsity and nonuniform distribution of diffractions for smooth lateral velocity change conditions. Application in a SCS line acquired in the Joetsu Basin, Japan Sea, indicates improvement in the focusing of deeper events compared to the previous processing flow, and it adds consistent information about the acoustic properties of the subsurface.