Retention mechanism on phosphodiester stationary phases in HILIC and purely aqueous mobile phase, Part I: The problem of hold-up volume determination.

Non-destructive chromatographic methods were used to determine the hold-up volumes of four self-packed columns containing embedded phosphate groups. The stationary phases are named Diol-P-C10, Diol-P-C18, Diol-P-Benzyl and Diol-P-Chol. The hydrophobicity of organic ligands bound to the phosphate group increases in the benzyl< decyl < octadecyl View Article and Find Full Text PDF

The Impact of Water as an Additive on the Elution of Some Basic Organic Compounds in Supercritical Fluid Chromatography.

In this study, water was used as an additive in the methanol-modified carbon dioxide-based eluent for the elution of some basic organic compounds from a hybrid silica column via supercritical fluid chromatography (SFC). The experiments were applied to sulfonamides, propranolol, and other organic nitrogen compounds involving aromatic rings from different classes of amine, pyrimidine, and purine with different pKa values (the pKa values for the studied analytes range from 4.6 to 10.

Exploring the application limits of different hold-up time markers in supercritical fluid chromatography.

The study focuses on the application range of nitrous oxide as a hold-up time marker in supercritical fluid chromatography (SFC). This compound has been suggested a decade ago to be used as unretained marker, something that the field of SFC was missing for a long time, since its beneficial properties make it an ideal candidate as hold-up time marker. Determination of the hold-up volume and actual volumetric flow rates have always been problematic in SFC due to the compressibility of carbon dioxide and one part of this is the difficulty of hold-up time measurements.

Retention mechanism on phosphodiester stationary phases in hydrophilic interaction liquid chromatography and purely aqueous mobile phase part II: Overloading with limited soluble samples.

The adsorption behaviour of caffeine and theophylline under hydrophilic interaction chromatography and purely aqueous conditions was investigated on four phosphodiester stationary phases. Solute adsorption isotherms were determined by frontal analysis or inverse method. The bi-Langmuir model was found to be the best choice to describe the behaviour of caffeine and theophylline adsorption in purely aqueous conditions, whereas the bi-Moreau model describes the adsorption phenomena in HILIC conditions.

Correctness of the van 't Hoff analysis for homogeneous or heterogeneous retention.

It is already known that the physical meaning of the numerical values of the calculated enthalpy (ΔH) and entropy (ΔS) change in chromatography via the van 't Hoff plot analysis is rather questionable. In the former work of these authors, it has been demonstrated that by serially coupling two reversed-phase columns of the same inner diameter but of different retention mechanism, the obtained thermodynamic values are not related to the numerical results obtained on the individual columns respectively. Since surface heterogeneity of the stationary phase is intrinsically present in chiral chromatography (enantioselective and non-selective sites), the calculation of ΔH and ΔS should be revisited in that field.

The impact of placement, experimental conditions, and injections on mass flow measurements in supercritical fluid chromatography.

In supercritical fluid chromatography (SFC), the variation of pressure, temperature and volumetric flow-rate is most noticeable when the mobile phase contains only neat carbon dioxide. This can be explained by the compressibility of CO and introduces several difficulties to the work of chromatographers. The only flow parameter that is considered to be constant across the SFC system is the mass flow-rate.

The adsorption of methanol on reversed phase stationary phases in supercritical fluid chromatography.

The surface excess isotherms of methanol from carbon dioxide on reversed phase stationary phases under two different operational conditions - which can be considered subcritical and supercritical conditions depending on the molar fraction of CO in methanol - were determined using the minor disturbance peak method. The shapes of the surface excess isotherms were very similar in subcritical and supercritical conditions for the same column. To verify the influence of the sample solvent on the separation efficiency, two solvents methanol and heptane were used as sample solvents for alkylbenzene samples for the separation on the studied columns with pure carbon dioxide mobile phase.

Separation of enantiomers of chiral basic drugs with amylose- and cellulose- phenylcarbamate-based chiral columns in acetonitrile and aqueous-acetonitrile in high-performance liquid chromatography with a focus on substituent electron-donor and electron-acceptor effects.

In this study, amylose- and cellulose-phenylcarbamate-based chiral columns with different chiral-selector (CS) chemistries were compared to each other for the separation of enantiomers of basic chiral analytes in acetonitrile and aqueous-acetonitrile mobile phases in HPLC. For two chemistries the amylose-based columns with coated and immobilized CSs were also compared. The comparison of CSs containing only electron-donating or electron-withdrawing substituents with those containing both electron-donating and electron-withdrawing substituents showed opposite results for the studied set of chiral analytes in the case of amylose and cellulose derivatives.

The correctness of van 't Hoff plots in chiral and achiral chromatography.

van 't Hoff plots (logarithm of the retention factor, ln k, vs. the reciprocal of absolute temperature, 1/T) are commonly used in chromatographic studies to characterize the retention mechanisms based on the determined enthalpy (ΔH) and entropy (ΔS) change of analyte adsorption. In reversed phase liquid chromatography, the thermodynamic parameters could help to understand the retention mechanism.

The effect of column packing procedure on column end efficiency and on bed heterogeneity - Experiments with flow-reversal.

The effect of column end structure and bed heterogeneity of six commercially available reversed-phase chromatographic columns for fast liquid chromatography with different column packing materials - such as fully porous (Waters XBridge C with 1.7 μm particles) and superficially porous (Waters CORTECS C with 1.6 μm particles), with column dimension of 2.

Modeling the competitive adsorption of sample solvent and solute in supercritical fluid chromatography.

Uncommon retention behavior of a series of n-alkylbenzene homologues as well as the effect of different sample solvents on chromatographic efficiency were studied in supercritical fluid chromatography. After testing various columns, an alkylamide stationary phase was selected for detailed studies. The results showed that even a small amount of methanol originating only from the sample, overloaded the column and competitive adsorption was induced between the analytes and the sample solvent for adsorption on the stationary phase.

Subantimicrobial Dose Doxycycline Worsens Chronic Arthritis-Induced Bone Microarchitectural Alterations in a Mouse Model: Role of Matrix Metalloproteinases?

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease hallmarked by irreversible damage of cartilage and bone. Matrix metalloproteinases (MMPs) involved in connective tissue remodeling play an important role in this process. Numerous MMPs have been examined in humans and animals, but their functions are still not fully understood.

The use of alteration analysis in supercritical fluid chromatography to monitor changes in a series of chromatograms.

Two-dimensional correlation analysis (2DCOR) is a unique chemometric method introduced in spectroscopy which became successful in a wide range of analytical fields. It was applied in chromatography as well but has not gained wide-spread popularity. In our previous work, we introduced an alternative method, Alteration Analysis (ALA), which is built upon the basic properties of 2DCOR, but it is fine-tuned for chromatographic applications and can be used on higher dimensional data sets as well.

Characterization of radial and axial heterogeneities of chromatographic columns by flow reversal.

The impact of the column length (5, 10, and 15 cm) and packing mode (constant pressure and constant flow rate up to 15,000 psi) on the radial and axial heterogeneities of 3.0 mm i.d.

The effect of the frictional heat on retention and efficiency in thermostated or insulated chromatographic columns packed with sub-2-μm particles.

The mass-transfer properties of a core-shell packing material with 1.6 μm particle diameter, and that of a fully porous packing material with 1.7 μm particle diameter were investigated and compared.

Rate constant determination of interconverting enantiomers by chiral chromatography using a stochastic model.

It may happen under the conditions employed that enantiomers interconvert to each other. In this case, obviously, the kinetics of the process is to be examined. When enantiomers dynamically interconvert to each other during the separation process, a plateau is observed between the adjacent peaks (so-called Batman peak appears).

Correction to: Use of non-living lyophilized Phanerochaete chrysosporium cultivated in various media for phenol removal.

In the original publication of this paper, the Acknowledgements section is missing the statement below.

Influence of pressure on the retention of resorcinarene-based cavitands.

The thermodynamics of the retention mechanism of resorcinarene-based cavitands in RPLC as well as the nature of the binding sites have been studied recently. In the present study, the influence of pressure on the retention of the cyclic tetramers on alkylsilyl and polar-embedded C and C stationary phases is investigated using aqueous methanol mobile phase. The pressure effect for cavity-shaped molecules has been scarcely studied so far.

Use of non-living lyophilized Phanerochaete chrysosporium cultivated in various media for phenol removal.

The biosorption of phenol on non-living lyophilized mycelial pellets of Phanerochaete chrysosporium cultivated in liquid medium of various compositions was studied in batch biosorption system. The fungal cell surfaces were characterized by FTIR spectroscopy and specific surface charge determination. The sorption kinetics and equilibrium were evaluated using linear and non-linear regression.

Multilayer adsorption in liquid chromatography - The surface heterogeneity below an adsorbed multilayer.

A numerical method was introduced for the estimation of the surface heterogeneity below an adsorbed multilayer of the analyte. The calculation procedure is based on the raw adsorption isotherm data points obtained by frontal analysis experiments. To permit the mapping of the nature of the analyte-surface interaction, a numerical procedure was used to pre-estimate the adsorbate-adsorbate interactions occurring during the adsorption process.

Investigation of the temperature dependence of water adsorption on silica-based stationary phases in hydrophilic interaction liquid chromatography.

In the present work, the adsorption of water was investigated in aqueous normal-phase liquid chromatography on Cogent Silica C and Cogent Phenyl hydride stationary phases at different temperatures by frontal analysis - using coulometric Karl Fischer titration - to compare the temperature dependence of adsorption of water from aqueous acetonitrile. The Cogent Silica-C and Cogent Phenyl Hydride columns have a silicon hydride surface (silica hydride) with less than 2% free silanol group; therefore, they do not have a strong association with water. The adsorption behavior of water on the mentioned stationary phases was modeled by Langmuir isotherm.

Comparison of the kinetic performance of different columns for fast liquid chromatography, emphasizing the contributions of column end structure.

The kinetic performance of five chromatographic columns designed for fast liquid chromatography with different column packing materials - including fully porous (2.0 and 1.9μm particles), core-shell (2.

Investigation of retention mechanism of resorcinarene based cavitands by linear and nonlinear chromatography.

Cavitands are cavity-shaped cyclic oligomers and they can create host-guest interactions with various analytes, therefore they have applications in supramolecular chemistry, nanoscale reactions, chromatographic separations, drug encapsulation and delivery, biochemistry. The investigation of the chromatographic behavior of large molecules, such as resorcinarenes and cavitands is meager up to now. To understand the retention of resorcinarenes and cavitands in liquid chromatography, we studied their retention mechanism by the thermodynamic parameters calculated from the van't Hoff equation and by generation of an adsorption isotherm, which can describe the adsorption of the solute on the stationary phase surface.

Bioactive Constituents and Antioxidant Activity of Some Carpathian Basin honeys.

Unifloral honeys have a high commercial value and should undergo a strict quality control before marketing. This study aimed at determining floral origin, polyphenolic compounds and antioxidant activity in 7 samples marketed as lavender and thyme honeys. The samples were subjected to pollen analysis to confirm their botanical origin.