Recent advances in nonpolar and polar organic monoliths for HPLC and CEC

Color Stability of Resin Hybrid Ceramic Materials in Comparison to Zirconia-Reinforced Lithium Silicate Ceramic

Objectives: This in vitro study aimed to compare the effect of external staining agents (black tea and grape juice) on the color change of three hybrid ceramics including a new material in comparison to zirconia-reinforced lithium silicate. Materials and Methods: Ten samples of two hybrid dental ceramics including Vita Enamic (Vita Zahnfabrik) and Crystal Ultra (Digital Dental) in addition to a resin nanoceramic, Lava Ultimate (3M ESPE); and a zirconia-reinforced lithium silicate glass ceramic, Vita Suprinity (Vita Zahnfabrik) were prepared and immersed in black tea or grape juice for 30 days. A spectrophotometer was used to evaluate color change. All samples were carefully chosen in A3 shades or their equivalent. Two-way ANOVA and Bonferroni tests were used to analyze the color differences (ΔE00) among the materials and the staining solutions at a significant level of 0.05. Results: Significant color changes were observed in Vita Enamic and Lava Ultimate groups after immersion in both solutions (P<0.001). The least color changes (ΔE00) belonged to the Vita Suprinity (1.34) and Crystal Ultra (1.92) groups, respectively. Conclusion: The color changes of Vita Enamic and Lava Ultimate materials were beyond clinical acceptability. However, the mean color changes of Vita Suprinity and Crystal Ultra groups were clinically acceptable.

Preparation of poly(N-vinylpyrrolidone-co-pentaerythritol triacrylate) monolithic column for hydrophilic interaction chromatography

A method for the preparation of poly(N-vinylpyrrolidone-co-pentaerythritol triacrylate copolymerization)-based monolithic capillary column was reported for the separation of polar small molecular weight compounds with nano-liquid chromatography in hydrophilic interaction chromatography mode. The monolithic columns were prepared by in situ copolymerization of N-vinylpyrrolidone and a cross-linker pentaerythritol triacrylate in a binary porogenic agent consisting of methanol and water. The composition of the polymerization solution was systematically optimized in terms of column permeability, theoretical plate number, asymmetric factor, and retention factor. A typical hydrophilic chromatography retention mechanism was observed with a mobile phase composed of a high content of organic solvent. The preparation method is simple and robust, the precursor N-vinylpyrrolidone is chemically stable, cheap, and easily available. The N-vinylpyrrolidone-based hydrophilic interaction chromatography stationary phase displays satisfactory separation selectivity for a range of polar test analytes, including benzoic acid derivatives, nucleosides, and phenols.

A benzenesulfonic acid-modified organic polymer monolithic column with reversed-phase/hydrophilic bifunctional selectivity for capillary electrochromatography

Here, a styrene-based polymer monolithic column poly(VBS-co-TAT-co-AHM) with reversed-phase/hydrophilic interaction liquid chromatography (RPLC/HILIC) bifunctional separation mode was successfully prepared for capillary electrochromatography by the in situ polymerization of sodium p-styrene sulfonate (VBS) with cross-linkers 3-(acryloyloxy)-2-hydroxypropyl methacrylate (AHM) and 1,3,5-triacryloylhexahydro-1,3,5-triazine (TAT). The preparation conditions of the monolith were optimized. The morphology and formation of the poly(VBS-co-TAT-co-AHM) monolith were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The separation performances of the monolith were evaluated systematically. It should be noted that the incorporation of VBS functional monomer can provide π-π interactions, hydrophilic interactions, and ion-exchange interactions. Hence, the prepared poly(VBS-co-TAT-co-AHM) monolith can achieve efficient separation of thiourea compounds, benzene series, phenol compounds, aniline compounds and sulfonamides in RPLC or HILIC separation mode. The largest theoretical plate number for N,N'-dimethylthiourea reached 1.7 × 10⁵ plates/m. In addition, the poly(VBS-co-TAT-co-AHM) monolithic column showed excellent reproducibility and stability. This novel monolithic column has great application value and potential in capillary electrochromatography (CEC).

Poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith with bonded anthracenyl ligands for use in reversed-phase capillary electrochromatography based on hydrophobic and π-π interactions

In this research report, the post polymerization functionalization (PPF) of a carboxyethyl acrylate (CEA)-co-ethylene glycol dimethacrylate (EDMA) [poly-CEA-co-EDMA)] precursor monolith with 2-aminoanthracene was carried out in the presence of an organic solvent soluble carbodiimide, namely N,N´-dicyclohexylcarbodiimide (DCC), yielding the so-called anthracenyl-poly-CEA-co-EDMA monolith. This novel monolith proved to be an excellent monolithic stationary for reversed-phase capillary electrochromatography (RP-CEC) with hydrophobic and π-π interactions of a wide range of nonpolar solutes including those bearing aryl functional groups in their structures such as polycyclic aromatic hydrocarbons (PAHs), toluene derivatives and aniline derivatives as well as solutes carrying in their structures electron withdrawing substituents such as dinitrophenyl-amino acids (DNP-AAs) and di-DNP-AAs. The retention behaviors of the just mentioned solutes obtained on the anthracenyl-poly-CEA-co-EDMA monolithic column were compared to those obtained on octadecyl-poly-CEA-co-EDMA monolithic column prepared from the same carboxy-precursor monolith. The results demonstrated the superiority of anthracenyl column over the octadecyl column for the separation and enhanced selectivity for aromatic solutes since it provides not only hydrophobic interactions but also π-π interactions with aromatic nonpolar solutes.

Benzoic acid-modified monolithic column for separation of hydrophilic compounds by capillary electrochromatography with high content of water in mobile phase

Hydrophilic column combined with mobile phase containing high content of water is a green method for the separation of polar compounds, but there are few related studies, and the separation efficiency and performance of existing columns still needs to be improved. In this work, a novel monolithic column for separation of hydrophilic compounds under both high water content and HILIC condition, was prepared by in-situ polymerization using 4-vinylbenzoic acid (VBA) and 1-(Acryloyloxy)-3-(methacryloyloxy)-2-propanol (AMAP) as functional monomers. The poly(VBA-co-AMAP) monolithic column showed good separation performance towards various polar compounds under different chromatographic conditions based on the π-interaction, hydrophobic and hydrogen bonding interactions provided by 4-vinylbenzoic acid functional monomer. The highest column efficiency for adenine was over 2.15 × 10⁵ plates m^-1 (theoretical plate, N). In addition, the monolith showed good stability and reproducibility, the relative standard deviations (RSDs) of retention times within days (n = 5), between days (n = 5), between columns (n = 3) and between batches (n = 3) were 0.47-1.13%, 1.20-2.68%, 0.59-1.78% and 1.54-3.60%, respectively. This novel type of monolith has great application potential in the separation of hydrophilic compounds.

Preparation of Benzyl Quinine-modified Monolithic Column for Reversed-phase Capillary Electrochromatography

N-Benzylquininium chloride is a versatile functional monomer with quinoline and benzyl groups, which is beneficial for reversed-phase chromatography. In this study, a novel monolithic column with reversed-phase mode was synthesized using N-benzylquininium chloride as the monomer and 3-(acryloyloxy)-2-hydroxypropyl methacrylate as the cross-linker in a binary porogenic solvent consisting of PEG 400 and a 0.05 M sodium hydroxide aqueous solution. The alkaline solution were found to be useful for the improvement of the mechanical stability of the porous monoliths. The monolithic column showed excellent reversed-phase selectivity and various compounds, such as alkylbenzenes, phenols and polycyclic aromatic hydrocarbons, were separated successfully. The highest column efficiency was 1.75 × 10⁵ N m^-1. The relative standard deviations of the migration time for thiourea and four alkylbenzenes were all less than 5.0%, which indicates the monolithic column has good stability. The application of the monolithic column for the analysis of polycyclic aromatic hydrocarbons in spiked lake water samples illustrated its great potential for practical application.

Monolithic capillary columns consisting of poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) and their diol derivatives with incorporated hydroxyl functionalized multiwalled carbon nanotubes for reversed-phase capillary electrochromatography

Two types of monolithic stationary phases with incorporated hydroxyl functionalized multiwalled carbon nanotubes (OH-MWCNTs) were introduced and evaluated, namely, the poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monolith, denoted as poly(GMA-co-EDMA), and a diol derivative of the poly(GMA-co-EDMA) monolith. The diol derivative monolith was obtained by subjecting the poly(GMA-co-EDMA) monolith with physically incorporated OH-MWCNTs to an acid treatment with 0.1 M sulfuric acid at a moderate temperature of 50 °C for a total of 7.5 h. Also, the poly(GMA-co-EDMA) monolith with both physically and covalently incorporated OH-MWCNTs was prepared by subjecting the physically incorporated monolithic column to a Lewis acid catalyzed reaction in the presence of BF₃ in order to react some of the OH-MWCNTs with the epoxy rings of the poly(GMA-co-EDMA) monolith. In all cases, the OH-MWCNTs were subjected to high power sonication at an output power of 10 W for 15 min with the aim of better dispersing the incorporated nanotubes into the monoliths under investigation. In fact, high power sonication yielded columns with a relatively higher plate count (∼2 fold increase) when compared to low power sonication. While the incorporation of OH-MWCNTs into the poly(GMA-co-EDMA) monolith acted as an amendment boosting the nonpolar character of the monolith and providing additional π-π interactions, the diol derivative monolith with its polar backbone character acted nearly as a support for the OH-MWCNT stationary phase giving rise to a carbon nanotube sorbent providing hydrophobic and π-π interactions via the incorporated OH-MWCNTs. These two kinds of columns were evaluated using alkylbenzenes, toluene derivatives, aniline compounds, phenols and polyaromatic hydrocarbons.

Chromatographic behavior of new deazapurine ribonucleosides in hydrophilic interaction liquid chromatography

The chromatographic behavior of new biogenic purine nucleosides in hydrophilic interaction liquid chromatography was examined on three different stationary phases, namely bare silica, and amide- and cyclofructan-based stationary phases. The effects of buffer concentration, pH and acetonitrile-to-aqueous-part ratio in the mobile phase on retention and peak shape were assessed. The retention coefficients and peak symmetry values substantially differed with respect to analytes´ structures, stationary phase properties and mobile phase composition. The bare silica column was unsuitable for these compounds under the chromatographic conditions tested due to very broad and asymmetrical peaks. Furthermore, the cyclofructan-based stationary phase provided almost Gaussian peak shapes of all deazapurine nucleosides under most conditions tested. Therefore, the cyclofructan-based stationary phase is the most suitable choice for the chromatographic analysis of nucleosides.

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.

Recent developments in capillary and microchip electroseparations of peptides (2015-mid 2017)

The review brings a comprehensive overview of recent developments and applications of high performance capillary and microchip electroseparation methods (zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography) to analysis, microscale isolation, purification, and physicochemical and biochemical characterization of peptides in the years 2015, 2016, and ca. up to the middle of 2017. Advances in the investigation of electromigration properties of peptides and in the methodology of their analysis (sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, and detection) are described. New developments in particular CE and CEC methods are presented and several types of their applications to peptide analysis are reported: qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC methods to provide important physicochemical characteristics of peptides are demonstrated.

Preparation of phosphorylcholine-based hydrophilic monolithic column and application for analysis of drug-related impurities with capillary electrochromatography

A hydrophilic monolithic CEC column was prepared by thermal copolymerization of zwitterionic monomer 2-methacryloyloxyethyl phosphorylcholine (MPC), pentaerythritol triacrylate (PETA), either methacrylatoethyl trimethyl ammonium chloride (META) or sodium 2-methylpropene-1-sulfonate (MPS) in a polar binary porogen consisting of methanol and THF. A typical hydrophilic interaction LC retention mechanism was observed for low-molecular weight polar compounds including amides, nucleotides, and nucleosides in the separation mode of hydrophilic interaction CEC, when high content of ACN (>60%) was used as the mobile phase. The effect of the electrostatic interaction between the analytes and the stationary phase was found to be negligible. The poly(MPC-co-PETA-co-META or MPS) monolithic columns have an average column efficiency of 40 000 plates/m and displayed with a satisfactory repeatability in terms of migration time and peak areas. Finally, the column was successfully applied to determine the impurities of a positively charged drug pramipexole which are often separated by ion pair RP chromatography due to their high hydrophilicity. All four components can be baseline separated within 5 min with BGE consisting of ACN/20 mM ammonium formate buffer (pH 3.0; 80/20).

Monolithic stationary phases with incorporated fumed silica nanoparticles. Part I. Polymethacrylate-based monolithic column with incorporated bare fumed silica nanoparticles for hydrophilic interaction liquid chromatography

Fumed silica nanoparticles (FSNPs), were incorporated for the first time into a polymethacrylate monolithic column containing glyceryl monomethacrylate (GMM) and ethylene dimethacrylate (EDMA) in order to develop a new monolithic column for hydrophilic interaction high performance liquid chromatography (HILIC). When compared to poly(GMM-EDMA) monolithic column without FSNPs, the same monolithic column with incorporated FSNPs yielded important effects on HILIC separations. The effects of monomers and FSNPs content of the polymerization mixture on the performance of the monolithic column were examined in details, and the optimized stationary phase was investigated over a wide range of mobile phase composition with polar acidic, weakly basic and neutral analytes including hydroxy benzoic acids, nucleotides, nucleosides, dimethylformamide, formamide and thiourea. The retention of these analytes was mainly controlled by hydrophilic interactions with the FSNPs and electrostatic repulsion from the negatively charged silica surface in the case of hydroxy benzoic acids and nucleotides. The electrostatic repulsion was minimized by decreasing the pH of the aqueous component of the mobile phase, which in turn enhanced the retention of acidic solutes. Nucleotides were best separated using step gradient elution at decreasing pH as well as ACN concentration in the mobile phase. Improved peak shape and faster analysis of nucleosides were attained by a fast linear gradient elution with a shallow decrease in the ACN content of the ACN-rich mobile phase. The run-to-run and column-to-column reproducibility were satisfactory. The percent relative standard deviations (%RSDs) for the retention times of tested solutes were lower than 2.5% under isocratic conditions and lower than 3.5 under gradient conditions.

Cardiovascular drug determination in bioanalysis: an update

The great impact of cardiovascular diseases in human health has led to the development of a huge number of drugs and therapies to improve the treatment of these diseases. Cardiovascular drug analysis in biological fluids constitutes an important challenge for analytical scientists. There is a clear need for reliable methods to carry out both qualitative and quantitative analysis in a short time of analysis. Different problems such as drug monitoring, analysis of metabolites, study of drugs interactions, drugs residues or degradation products, chiral separation, and screening and confirmation of drugs of abuse in doping control must be solved. New trends in sample preparation, instrumental and column technology advances in LC and innovations in MS are described in this work.