Composite Stationary Phase Research Articles

Micro gas chromatographic column with copper benzene-1,3,5-tricarboxylate modified by multilayer fluorinated graphene as a stationary phase

A composite material was synthesized at room temperature by performing modification of the copper benzene-1,3,5-tricarboxylate (HKUST-1) metal-organic framework material by multilayer fluorinated graphene (FG). The FG-HKUST-1 composite was used as a stationary phase for a micro gas chromatography column (μGCC) fabricated using micro-electro-mechanical system (MEMS) technology. The separation results showed that the μGCC with the FG-HKUST-1 composite stationary phase achieved a baseline separation of C1-C4 in 8 min. The retention factors for C2-C4 were 2.13, 7.14, and 12.04, respectively. The maximum relative standard deviation (RSD) of the retention times was 0.14 %. The difference in the retention time between methane and ethane was 1.11 min, with a resolution of 9.2 for methane and ethane. The retention factor of ethane and the resolution of methane and ethane were increased by 166 % and 114 %. Therefore, this μGCC is promising for separating light hydrocarbons with widely differing concentrations.

Micro gas chromatography column coated with ionic liquid/metal–organic framework composites as the stationary phase

In this paper, the μGC-IL/MOF and the μGC-IL were prepared using [P66614][NTf2]/ZIF-8 and [P66614][NTf2] as the stationary phase, respectively. [P66614][NTf2]/ZIF-8 composite stationary phase material has high specific surface area and porous structure, which increases the diffusion of gas molecules in the column. Compared to μGC-IL, μGC-IL/MOF can separate n-alkanes mixture (C5–C12) and lung cancer biomarkers (pentane, isoprene, acetone, benzene, 2-pentanone) with higher resolution, and the resolution (R) of pentane and isoprene was increased by 257.00% in particular. The μGC-IL/MOF can separate lung cancer biomarkers in about 5 min with optimal carrier gas velocity and column temperature. The retention times of pentane, isoprene, acetone, benzene, and 2-pentanone were 0.884 min, 1.246 min, 1.634 min, 2.204 min, and 3.049 min, respectively. The resolutions of adjacent peaks were 1.785, 1.525, 2.521, and 3.514, respectively. Which meets the requirements of quantitative analysis (R > 1.5). Therefore, the μGC-IL/MOF is expected to be integrated into portable devices for environmental monitoring and medical diagnosis in the future.

A new strategy for the preparation of core-shell MOF/Polymer composite material as the mixed-mode stationary phase for hydrophilic interaction/ reversed-phase chromatography

A facile method for efficient synthesis of core-shell composite material was proposed. In this method, the silica microspheres were co-modified with metal organic framework (MOF-235) and polyethylene glycol polymer (PEG) and used as mixed-mode stationary phase (MOF-235@PEG@silica) for high-performance liquid chromatography. Elemental analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Brunauer-Emmett-Teller etc. methods were used to investigate the properties of the core-shell composite material. The MOF-235@PEG@silica stationary phase showed flexible selectivity for the separation of both hydrophilic and hydrophobic compounds especially for the separation of nine alkaloids, which showed superior hydrophilic separation performance than previous MOF-based composite stationary phases. Some factors including the pH of buffer salt, the ratio of organic phase and water phase in the mobile phase have been investigated, suggesting that the chromatographic retention mechanism of the column was a mixed mode of hydrophilic and reversed phase. The composite material also showed excellent chromatographic repeatability with the RSDs of the retention time found to be 0.2%–0.6% (n = 10) and the standard addition test in the actual sample proved that it can be used for practical sample analysis. In short, it provided a general way for preparing MOFs-based composites as mixed-mode chromatographic stationary phases, and changed the current status of MOF-based composite materials as single mode chromatographic stationary phases.

New composite stationary phase for chiral high-performance liquid chromatography

The new composite chiral stationary phase for high-performance liquid chromatography was prepared and characterized. Poly(styrene-divinylbenzene) microspherical particles with diameter of 3.3 micron were used as a matrix and coated with layer of 10 nm gold nanoparticles. Immobilized gold nanoparticles increased specific surface area of adsorbent and simplify covalent attachment of sulfur-containing compounds. In this work l-lysine conjugate with lipoic acid was synthesized, characterized and used for modification of gold nanoparticles. The prepared chiral selector was immobilized by the reaction of sulfur-containing groups from lipoic acid residue with gold surface of nanoparticles with formation of self-assembled monolayer. The prepared chiral stationary phase was characterized by nitrogen adsorption at low temperatures, diffuse reflection spectroscopy, scanning electron microscopy. The chromatographic retention of beta-blockers and profens was studied under conditions of reversed-phase HPLC. The possibility of enantiomers separation was demonstrated for flurbiprofen and ketoprofen racemates using 100 × 4.6 mm ID chromatographic column.

Synthesis and chromatographic evaluation of poly(pentabromostyrene)-silica composite: A versatile stationary phase for separating both polar and non-polar aromatic compounds

Polymer-silica composite materials have been witnessed as one of the most promising chromatographic packing materials. The demands of novel stationary phases are always existing due to the requirements for the separation of special samples. In our present work, the novel poly(pentabromostyrene)-silica composite stationary phases were successfully prepared by surface initial free-radical polymerization. The polymer chains bonding on the surface of the poly(pentabromostyrene) contain plenty of phenyl moiety, which provide hydrophobic and π-π interactions between the stationary phase and analytes. Besides, the bromide atoms, existing in the polymer, provide extra polar interaction with polar or easily polarized analytes. Compared with the typical C18 stationary phase, the novel stationary phase showed special separation selectivity. Samples, including polycyclic aromatic hydrocarbons, phenols, anilines, amino acids, halogenated benzenes, acetophenone derivatives, benzene homologous compounds, were all well separated by the new stationary phase. Also, the great stability (0.13% ≤ RSDs ≤ 0.98%, n = 5) of packed columns and the good synthesis repeatability were demonstrated. Finally, the new columns were applied to the separation of fullerenes. The loading ratio reached 2.67% (36 mg of fullerenes was loaded onto the column packed with 1.35 g stationary phase), with high yield (86.3%) of high pure C60 (>95%). This novel stationary phase has a great potential to be a complementary to traditional C18 column and a special column for fullerenes separation.

Graphene quantum dots-functionalized C18 hydrophobic/hydrophilic stationary phase for high performance liquid chromatography

Graphene quantum dots (GQDs) were chosen as functional material to improve the separation performance of C18 column since GQDs could provide multiple interactions such as hydrophilic, π-π stacking and hydrogen bonding interactions. In this study, a novel octadecyl modified GQDs-bonded silica (C18/GQDs/SiO2) stationary phase was prepared and applied in reversed-phase and hydrophilic interaction liquid chromatography. This column showed satisfactory separation performance for both hydrophobic, polar and hydrophilic compounds including polycyclic aromatic hydrocarbons, alkylbenzenes, anilines, phenols, aromatic acids, alkaloids, nucleosides and nucleobases. Through investigating the impact of organic solvent content on retention, it was found this new stationary phase had typical characteristics of hydrophobic/hydrophilic chromatography. Compared with commercial C18 column, this column showed better separation performance for polar aromatic compounds because the introduction of GQDs provided more interactions such as π-π stacking, hydrophilic and hydrogen bonding interaction with analytes. To get an in-depth understanding of the retention mechanism, linear solvation energy relationship model was established for both C18/GQDs/SiO2 and C18 columns, theoretically calculated data indicated that C18/GQDs/SiO2 column had higher π-π stacking and hydrogen-bonding acceptance ability. C18/GQDs composite stationary phase equipped with hydrophobic/hydrophilic properties has great prospect in separation science.

A novel composite stationary phase composed of polystyrene/divinybenzene beads and quaternized nanodiamond for anion exchange chromatography

An approach for preparation of a novel composite anion exchanger composed of polystyrene/divinylbenzene (PS/DVB) beads and quaternized nanodiamods (QND) were proposed. Oxidized nanodiamonds (OND) were quaternized by the condensation polymerization between methylamine (MA) and 1,4-butanediol diglycidyl ether (BDDE), which were characterized by Fourier transform infrared (FTIR) spectra, X-ray phtoelectron spectroscopy (XPS), thermogravimetric analysis (TGA). QND with layers of cationic polyelectrolyte was attached onto the surface of sulfonated PS/DVB beads electrostatically. Subsequently, hyperbranched reaction of QND agglomerated on the PS/DVB bead surface was performed by the alternate reaction between MA and BDDE to increase the exchange capacity. The composite anion exchanger showed good stability in organic solvent and a wide pH range. The surface of these microspheres was characterized by scanning electron microscopy. In addition, ion exchange selectivity and separation efficiency of the anion exchangers were assessed using the mixtures of anions (F−, Cl−, NO2−, Br−, NO3−, HPO42− and SO42−) with carbonate/bicarbonate as eluent, and the anion exchanger with high exchange capacity could be used to analyze chloride in aqueous solution with high concentration of fluoride. This work explores the potential of nanodiamods as an agglomerated material for ion chromatography stationary phases for the separation of inorganic anions.

Gold nanoparticle decorated graphene oxide/silica composite stationary phase for high-performance liquid chromatography.

In the initial phase of this study, graphene oxide (GO)/silica was fabricated by assembling GO onto the silica particles, and then gold nanoparticles (GNPs) were used to modify the GO/silica to prepare a novel stationary phase for high-performance liquid chromatography. The new stationary phase could be used in both reversed-phase chromatography and hydrophilic interaction liquid chromatography modes. Good separations of alkylbenzenes, isomerides, amino acids, nucleosides, and nucleobases were achieved in both modes. Compared with the GO/silica phase and GNPs/silica phase, it is found that except for hydrophilicity, large π-electron systems, hydrophobicity, and coordination functions, this new stationary phase also exhibited special separation performance due to the combination of 2D GO with zero-dimensional GNPs.

Amino-terminated ionic liquid modified graphene oxide coated silica composite stationary phase for hydrophilic interaction chromatography

IL@GO@SiO2 composite was synthesized and revealed good separation for three kinds of strong polar and hydrophilic compounds in HILIC mode.

A novel octadecylsilane functionalized graphene oxide/silica composite stationary phase for high performance liquid chromatography

An octadecylsilane functionalized graphene oxide/silica stationary phase was fabricated by assembling graphene oxide onto the silica particles through an amide bond and subsequent immobilization of octadecylsilane. The chromatographic properties of the stationary phase were investigated by reversed-phase chromatography with alkylbenzenes, polycyclic aromatic hydrocarbons, amines, and phenolic compounds as the analytes. All the compounds achieved good separation on the column. The comparison between a C18 commercial column and the new stationary phase indicated that the existence of π-electron system of graphene oxide allows π-π interaction between analyte and octadecylsilane functionalized graphene oxide/silica stationary phase except for hydrophobic interaction, while only hydrophobic interaction presented between analyte and C18 commercial column. This suggests that some analytes can be better separated on the octadecylsilane functionalized graphene oxide/silica column.

Preparation of Polysaccharide Derivatives-based Composite Chiral Stationary Phases and Their Chiral Recognition

Preparation of Polysaccharide Derivatives-based Composite Chiral Stationary Phases and Their Chiral Recognition

Chiral recognition of tryptophan enantiomers based on a polypyrrole‐flake graphite composite electrode column

AbstractA polypyrrole (PPy)‐flake graphite composite was synthesized by in situ polymerization of pyrrole on flake graphite surface, and the resulting organic–inorganic composite material was developed as the conductive stationary phase in an electrode column for enantioselective recognition of tryptophan (Trp) enantiomers. Compared with the stationary phase made up with conducting PPy, the conductivity of the composite stationary phase was enhanced significantly. As a result, satisfactory enantioselectivity of Trp enantiomers can be achieved easily by modulating the potential applied on the electrode column. Various important parameters influencing the performance of the composite electrode column were investigated to obtain the optimum recognition efficiency. A recognition efficiency of 3.7 could be achieved under the optimum conditions. Enantioselectivity of the composite material for Trp enantiomers is attributed to the reversible doping/de‐doping properties of PPy. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Layer-by-layer self-assembled graphene oxide/silica microsphere composites as stationary phase for high performance liquid chromatography

Graphene oxide (GO) has been layer-by-layer assembled onto silica microspheres to form a GO/SiO(2) composite stationary phase. All the characterizations of GO/SiO(2) by elemental analysis, Raman spectroscopy and Fourier transformed infrared spectrometry confirmed that with the increase of the assembled layer, GO gradually increases on the silica surface. The chromatographic properties of bare SiO(2) and GO/SiO(2) with different GO assembled layers show that the amount of GO plays an important role in the separation of analytes. Only the appropriate amount of GO on SiO(2) can perform a good chromatographic separation. The comparison between chromatographic performances of bare SiO(2) column, GO/SiO(2)-2 column and C18 commercial column clearly show that GO/SiO(2)-2 and C18 columns obtained a better separation; GO/SiO(2)-2 exhibits a large π-electron system and C18 exhibits hydrophobicity. The eluting order, peak width and resolution of analyte on GO/SiO(2)-2 column was highly dependent on the size of its π-electron system, while on the C18 column the decisive factor is its hydrophobic property.

Preparation of Polysaccharide Derivatives-based Composite Chiral Stationary Phases and Their Chiral Recognition Abilities

Abstract Two coated composite chiral stationary phases (CSPs) were prepared using tris(3,5-dimethylphenylcarbamate) of cellulose (CDMPC) and amylose (ADMPC) by coating the corresponding derivatives onto 3-aminopropyl silica gel separately and then mixing or by coating the mixed derivatives onto silica gel. The CSPs containing only CDMPC or ADMPC were also prepared for comparison. The mixing method does not significantly influence the enantioselectivities. The composite CSPs generally show chiral recognition abilities that are intermediate between those of the two individual phases, whereas some racemates were poorer and simultaneously, one pair of racemates were better resolved on the composite CSPs.

Characterisation of the chromatographic properties of a silica–polypyrrole composite stationary phase by inverse liquid chromatography

Silica–polypyrrole particles have been used as a composite stationary phase for liquid chromatography. Determination of capacity factors ( k′) of a wide number of polycyclic aromatic hydrocarbon (PAH) molecular probes allows the characterisation of the chromatographic properties of the silica–polypyrrole stationary phase. Capacity factors in the range of 0.10 up to 6.1 were determined, thus demonstrating the high affinity of the PAH probes towards the stationary phase. The selectivity of the composite stationary phase was also evaluated as a function of the planarity of the molecular probes injected. Capacity factors determined for PAHs (two-dimensional molecular probes) are higher than those measured for phenyl-substituted PAHs (phenyl-PAHs, three-dimensional molecular probes). Determination of capacity factors, dependence on the composition of the mobile phase demonstrates the reverse α-phase properties of the composite stationary phase. The acid–base properties of the composite silica–polypyrrole stationary phase were investigated using benzene derivative molecular probes (i.e., toluene, phenol, benzoic acid and aniline). Capacity factors in the range of 0.45 to 1.0 were determined. This study clearly demonstrates that this composite stationary phase exhibits selective interactions towards PAHs and phenyl-substituted PAHs and strong acid–base properties depending on the structure, the geometry and the acid–base properties of the molecular probes eluted.

RETENTION BEHAVIOR OF BASICA SOLUTES ON ZIRCONIA-SILICA COMPOSITE STATIONARY PHASE SUPPORTS IN NORMAL PHASE LIQUID CHROMATOGRAPHY

Impregnation of sodium iodide into the matrix of zirconia-silica composite stationary phases during calcination was shown to improve the band profiles of basic compounds analysed using these surfaces. These compounds (pyridine and aniline) displayed severe band distortion associated with interactions between Lewis acid sites or residual hydroxyl groups on columns that were not subjected to the sodium-iodide impregnation. On the sodium iodide impregnated stationary phase, pyridine and aniline eluted with band shapes similar to neutral solutes, such as benzene. Stationary phase materials of this nature may prove to be useful for the separation of basic solutes that are unstable in aqueous environments, and hence, demand normal phase separations in which residual hydroxyl groups are often a significant component of the stationary phase surface.

Retention behavior of basic compounds on alkylphosphonate-modified magnesia-zirconia composite stationary phase in RPHPLC

The chromatographic properties of an alkylphosphonate-modified magnesia-zirconia composite stationary phase have been investigated by reversed-phase high-performance liquid chromatography with basic compounds as probes. The influence of organic modifier composition and mobile phase pH was studied. The new stationary phase, similar to a silica-based reversed-phase stationary phase, has hydrophobic properties, but greater pH stability. Use of the phase results in more symmetric peaks for basic compounds. A possible mechanism of retention of basic solutes on the new stationary phase is discussed. The chromatographic behavior of the basic solutes depends mainly on hydrophobic interactions between the solutes and the hydrophobic moiety of the stationary phase. Bronsted acidic and basic sites on the surface of the new stationary phase play an important role in the retention of ionized solutes by ion-exchange interaction. Promising separations of some basic compounds have been achieved by use of methanolic TRIS buffer, pH 10.0, as the mobile phase.

PREPARATION AND CHARACTERIZATION OF SILICA-ZIRCONIA SUPPORTS FOR NORMAL-PHASE LIQUID CHROMATOGRAPHY

Two silica-zirconia composites with different silica molar ratio (3.4% and 15.8%, respectively) were prepared as rigid-micro spheres by means of a sol-gel process. Scan electron micrograph, X-rays diffraction, nitrogen adsorption, and potentiometric titration were used to characterize the silica-zirconia composites and, for the comparison, bare zirconia. Addition of the silica into the zirconia prevented the formation of monoclinic zirconia. The silica-zirconia composites show larger specific surface area and more ideal pore structure than the bare zirconia. The normal phase chromatographic performance was studied by using isopropanol/cyclohexane, dichloromethane/cyclohexane and chloroform/cyclohexane as mobile phases. Basic solutes gave symmetrical peaks, and the acidic solutes exhibited better peak shape on the composite stationary phases than on the bare zirconia.

The Development of Stationary Phase Supports For Liquid Chromatography. I. Examination of the Pore Structure of Zirconia-Silica Composites Using Size Exclusion Chromatography

In this first part of a two part series, the pore structure of zirconia-silica composite stationary phase supports was examined using size exclusion chromatography. The study found that the pore structure was more complex than pure zirconia surfaces. With these composite materials, the pore dimensions are primarily dependent on the concentration of the silicon doping, the temperature of calcination, and the presence of salts during calcination. Silicon concentration influences the phase crystallization which, in turn, alters the temperature at which micropores transform to mesopores. Calcination in the presence of sodium chloride increased the surface area and pore volume of the support.

Determination of the phase ratio by means of reaction kinetics in a liquid chromatographic reactor

The on-column rate constants in an octadecylsilane (ODS) bonded liquid chromatographic reactor with methanol mobile phase were used to determine the phase ratio and catalyst distribution coefficient. A concentration factor and the extent of ODS participation were introduced to treat the contribution of the non-polar alkyl ligands to solute retention in the composite stationary phase. The results obtained from this operational approach which can be expanded to other systems are quite comparable to literature values, and the discrepancies are discussed.