Mixed Stationary Phases Research Articles

Tetraethylenepentamine-derived carbon dots and tetraethylenepentamine co-immobilized silica stationary phase for hydrophilic interaction chromatography

In this work, tetraethylenepentamine (TEPA) was used as precursor and reaction medium to prepare tetraethylenepentamine-functionalized carbon dots (TEPACDs), the resultant mixture was subsequently silanized and then grafted on the surface of bare silica. The obtained tetraethylenepentamine-functionalized carbon dots and tetraethylenepentamine co-modified silica stationary phase (Sil-TEPA/CDs) was characterized by multiple ways, such as Fourier transformed infrared spectroscopy (FTIR), elemental analysis and transmission electron microscope, which revealed the successful preparation of the mixed stationary phase and higher density of functional groups on co-modified stationary phase than precursor single-modified stationary phase. The synergistic effect of TEPACDs and TEPA was proved by comparing the separation performance of Sil-TEPA/CDs and Sil-TEPA toward amino acids, nucleosides, and nucleobases, which distinctly enhanced the selectivity of Sil-TEPA/CDs. Thus, 12 nucleosides and nucleobases and 11 amino acids was nicely separated on Sil-TEPA/CDs. By study the influences of the changes of mobile phase composition, mobile phase buffer concentration and buffer pH on the retention behaviors of Sil-TEPA and Sil-TEPA/CDs, it was found that both hydrophilic partitioning and adsorption of analytes on Sil-TEPA/CDs were enhanced benefit from the co-existence of TEPA and TEPACDs, which provided the analytes better separation performance. By comparing the column quality of Sil-TEPA/CDs with four commercially available columns, Sil-TEPA/CDs exhibited the best peak asymmetry of 0.98, and second best column efficiency of 43895 m−1 using guanosine as analyte. The RSD (n = 9) of the retention times of five selected analytes on Sil-TEPA/CDs were within 0.30–0.61% during 40 h of continuously elution, which implied excellent stability of prepared packing material.

Synthesis, characterization and application of carbon nanotube-bonded with silica as a high performance liquid chromatography stationary phase

In order to improve the retention ability of anthraquinones and flavonoids on high performance liquid chromatography (HPLC) column and improve chromatographic performance, multi-walled carbon nanotubes (MWCNTs) were bound to the surface of silica spheres via amide bonding using a chemical synthesis method. Three hybrid fillers were prepared by varying the amount of MWCNTs added, and the stationary phases were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The successful preparation of the mixed stationary phases was demonstrated by comparing the changes in the surface of silica spheres before and after bonding and the changes in the absorption peaks of specific functional groups. The mixed stationary phases were filled in the empty column of the HPLC. The results of this study indicate that the columns can be prepared by CNTs@SiO2 to improve or broaden the chromatographic performance of the stationary phase and obtain better separation of the compounds. This thesis provides an idea for improving chromatographic performance with a view to playing a better role in the application of compound separation.

Смешанные хиральные неподвижные фазы в хроматографии (обзор)

Обсуждается использование смешанных селекторов в газовой и высокоэффективной жидкостной хроматографии для разделения оптических изомеров. Они позволяют повысить универсальность хиральной фазы. В газовой хроматографии широко и успешно используются смеси модифицированного β-циклодекстрина. В ВЭЖХ наиболее изучены смешанные хиральные селекторы на основенизкомолекулярных селекторов и производных полисахаридов, в меньшей степени ̶ белков и макроциклических антибиотиков.

Mixed Stationary Phase for TLC:Separation of Components from Manjistha Root Extract

Thin layer chromatography owes its popularity to several advantages, being faster, easy to perform and ability to use a variety of mobile phase compositions because detection is post mobile phase removal. Silica gel is the most commonly employed stationary phase. This poses certain limitations in terms of selectivity, hence suitable modifications are attempted. Selectivity can be improved using modified silica but the process of modification can be tedious and non reproducible. We report here use of mixed bed stationary phase for separation of components in extract of roots of Rubia cordifolia L. (family Rubiaceae), a common medicinal plant used in the preparation of various formulations in Ayurveda. Microcrystalline cellulose (MCC) was prepared and used as a stationary phase with silica in the ratio 10 : 90 and 5 : 95 w/w respectively. Mobile phase composition was optimized and an additional component was separated, which was not observed on silica TLC plate. Moreover, characterization studies of prepared MCC were performed. The FTIR spectra obtained resembled the commercial MCC spectra with all the characteristic peaks obtained well in the prepared MCC. The dynamic light scattering data of the prepared MCC showed the mean particle diameter of 0.715 μm. The TGA-DTA data showed no deviations in the plot, even when the analysis was carried out in the presence of air instead of nitrogen.

Speciation of 2′-deoxymugineic acid–metal complexes in top soil extracts by multi-modal stationary phase LC-ICP-MS

For the first time a mixed mode stationary phase was implemented for the speciation of 2′-deoxymugineic acid–metal complexes in soil related samples.

Characteristic variations of gas-chromatographic retention indices for phases of variable composition

On an example of mixtures of dinonyl phthalate and 2,2′-bis-(2-cyanoethoxy)diethyl ether, it was shown that the dependence of gas-chromatographic retention indices (RIs) on the composition (α) of mixed stationary phases can be both linear and with various abnormalities. These features of the dependence of RI-α can be explained by the existence of areas of homogeneity and disintegration of mixed phases. Another reason for the nonlinearity of the dependence RI-α is that the components of phases of variable composition are expressed in mole fractions, which is typical for polymethylphenylsiloxanes, widely used in contemporary gas chromatography. It is shown that the expression of composition in mass fractions enables the approximation of these dependencies in the homogeneity regions by linear regression equations with sufficient accuracy.

Physical Ionic Liquid/Polysiloxane Mixtures for Tuning the Polarity and the Selectivity of the Polysiloxane Stationary Phase for GC Analysis

Two novel room-temperature ionic liquids (RTILs), a mono-cationic (tetra-n-octylammonium) and a dicationic (bis-methylpiperidinium-butylidene) room-temperature ionic liquid with the bis[(trifluoromethyl)sulfonyl]imide anion, were individually mixed with OV-1701 polysiloxane to tune the selectivity and the polarity of stationary phases for GC. The interaction properties of the stationary phases were investigated on the basis of polarity calculations and the linear solvation energy relationship. The incorporation of the monocationic RTIL in the OV-1701 increased the dipolarity/polarizability capacities (s) and the hydrogen-bond basicity ability (a) allowing the separation of the m-chloroaniline/p-chloroaniline isomers and the m-xylene/p-xylene isomers which are not usually separated on polysiloxane stationary phase. The mixed stationary phases exhibited a greater selectivity than the OV-1701 phase for the majority of the aromatic compounds tested, demonstrating a kind of synergistic effect of the combination of polysiloxane and RTIL. The addition of RTIL proved to be an original method to modulate the polarity and the selectivity of the stationary phase of intermediate polarity in order to prepare stationary phases dedicated for specific separation with good durability (more than 20 months and more than 1,000 injections) and without any loss of thermal stability.

Preparation of mixed stationary phase of cellulose and polysiloxane ionic liquid for gas chromatography

Cellulose has been widely used to synthesize chiral stationary phases for liquid chro- matography, but it is still absent in the family of stationary phases of gas chromatography due to its poor film-forming property. Based on the unique dissolution characteristic, ionic liquids provide a great chance to solve this problem. In this paper, cellulose triacetate (CTA) was syn- thesized, and then mixed with the home-made polysiloxane ionic liquid (PIL-C12-NTf2) to pro- duce a novel mixed stationary phase (CTA@ PIL-C12-NTf2). After that, it was used to prepare a capillary column for gas chromatography. The column efficiency was measured to be 3,165 plates/m (110 °C, naphthalene, k = 4.95), demonstrating the excellent film-forming capability of this stationary phase, and then the solvation parameter model was employed to find out the interaction parameters of CTA@ PIL-C12-NTf2. In the aspect of selectivity, CTA was firstly demonstrated to be able to improve the resolutions of tri-substituted aromatic positional isomers and the six isomers of nonane (C9). Moreover, some mixtures of representative chemicals like di-substituted aromatic positional isomers, n-alkanes, alcohols, aliphatic esters and phthalates can also be separated well on CTA@ PIL-C12-NTf2. This work proposed a novel way for the application of cellulose modified stationary phase of gas chromatography, and revealed some features of this stationary phase in selectivity resulting from cellulose.

Versatile chiral chromatography with mixed stationary phases of water-impregnated silica gel and reversed-phase packing

A novel chiral chromatographic scheme is proposed, which requires no organic syntheses in stationary phase preparation. A normal phase chiral chromatography stationary phase is prepared by simple passage of an aqueous solution of an appropriate chiral selector through e.g. a silica gel column. For this scheme, a mixed-bed of bare silica gel and octadecylsilanized silica gel (ODS) provides much better separation performance than a silica gel column. Isolation of silica gel particles in the column is important for successful chiral separation based on the present scheme.

Gas-chromatographic studies of the sorption thermodynamics of adamantanes on a carbon adsorbent modified with polyethylene glycol with β-cyclodextrin additives

The thermodynamic characteristics of sorption of adamantane and its derivatives on a mixed stationary phase consisting of a graphite-like solid substrate, polyethylene glycol, and β-cyclodextrin (βCD) were determined by gas chromatography. The introduction of β-CD additives to a polar polymer matrix was shown to considerably decrease the chromatographic retention of the sorbates, which is evidence of the macrocyclic effect. The presence of β-CD molecules was found to increase the selective properties of the mixed sorbent with respect to the structural isomers of adamantanes.

Study of Chiral Ionic Liquid as Stationary Phases for GC

Due to the synthetic flexibility and special enantioselectivity, chiral ionic liquids (CILs) have heightened interest and an increasing number of CILs has been designed and utilized. In this work, CIL named l-1-butyl-3-(2-propionic-1-ether) imidazolium bromide ([BAlaIM]Br) derived from natural amino acids was synthesized, with chiral center at cation moiety. Chiral stationary phases for gas chromatography were then prepared by mixing the CIL with polymeric ionic liquid ([PSOMIM][NTf2], homemade) at different ratios (4:1, 2:1, and 1:1). The column efficiency was measured to be about 3,200 plates m−1 (8 m × 0.25 mm i.d.) when the content of [BAlaIM]Br was 50 % (mass percent) in the mixed stationary phase. All columns were coated via the static coating method using 0.30 % (w/v) of stationary phases dissolved in methanol. The results showed that the CIL contributed to the selectivity of stationary phase toward positional isomers dichlorobenzenes, methylnaphthalenes and pinenes, etc. Meanwhile, [BAlaIM]Br showed better selectivity for enantiomers such as carvones, citronellals, limonenes and camphors. The interactions between chiral selector and enantiomers were also discussed.

Separation of hydrocarbon and sulfur-containing gases on a new poly-(1-trimethylsilyl-1-propyne)/poly-(1-phenyl-1-propyne) mixed stationary phase in the presence of water

The separation of hydrocarbons (methane, ethane, propane, n-butane, ethylene, and propylene) and sulfur-containing gases (hydrogen disulfide, sulfur dioxide, carbonyl sulfide) on a new mixed stationary phase poly-(1-trimethylsilyl-1-propyne)/poly-(1-phenyl-1-propyne) in the presence of water has been studied by gas chromatography. It has been demonstrated that the new mixed stationary phase outperforms the known polymeric adsorbents and stationary phases by resolution, asymmetry factor, and column efficiency.

Chromatographic and adsorption properties of poly(1-trimethylsilyl-1-propyne) and their stabilization by adding poly(1-phenyl-1-propyne)

The chromatographic and adsorption properties of poly(1-trimethylsilyl-1-propyne) (PTMSP), a high permeable glassy polymer, were studied in the course of long-term usage of the Chromosorb P NAW+10wt% PTMSP adsorbent on a packed column in the temperature range of 30–180°C. The structural changes in PTMSP related to a decrease in free volume and partial oxidation of the polymer were shown to substantially affect the adsorbent's properties. After the first 1.5 years (7000h) of the column operation, the elution order of compounds changed, peak symmetry and efficiency of the column increased, the retention parameters as well as heats of adsorption of light hydrocarbons showed considerable changes. In order to stabilize the chromatographic properties of PTMSP, another disubstituted polyacetylene, poly(1-phenyl-1-propyne) (PPP), was added to the initial polymer, and a new mixed stationary phase, 97% PTMSP+3% PPP, was obtained and characterized. The resulting adsorbent, Chromosorb P NAW+10wt% (97% PTMSP+3% PPP), is effective for solving a wide range of chromatographic problems, such as simultaneous detection of hydrocarbons and sulfur-containing inorganic gases, analysis of chlorine-substituted methanes in CCl4 and thiophene in benzene, separation of hydrocarbons and aromatic compounds. The chromatographic properties of the Chromosorb P NAW+10wt% PTMSP (97% PTMSP+3% PPP) adsorbent were shown to remain stable in the course of its long-term operation (for at least 1.5 years, or 7000h) on a packed column in the temperature range of 30–180°C.

Simultaneous Determination of Some Analgesic Drugs Using Mixed Mode Stationary Phase

A new HPLC method based on a mixed mode stationary phase Hypersil Duet C18/SAX was developed and applied for the simultaneous determination of acetaminophen, acetylsalicylic acid and codeine. Parameters, such as the composition of the mobile phase, the nature of the organic modifier, the buffer type and the flow rate were investigated to optimize the separation. The results obtained show that the new HPLC method is rapid, highly efficient and selective. The studied compounds are separated in 10 min, by means of a mobile phase containing phosphate buffer (pH 7.50) and methanol (65:35 v v−1). The retention mechanisms of each analyte were investigated using both the linear solvent strength theory and stoichiometric displacement model. The method was fully validated and showed good linearity for each compound for a concentration ranging between 2.0 and 40 μg mL−1. The limits of detection and quantification were determined and they are lower than 0.1 μg mL−1. The precision (RSD) of the method does not exceed 2 % for all studied compounds. The method was successfully applied for the assay of acetaminophen, acetylsalicylic acid and codeine in pharmaceutical formulations.

Transport Characteristics of Aromatic Acids in the Capillary Electrochromatography with Mixed Magnetic Nanoparticles Coating as Stationary Phase

In this paper, novel open-tubular electrochromatographic system with core/shell magnetic nanoparticles modified by amino and C18 functional groups as mixed stationary phase by using a series of permanent magnets to immobilize nanoparticles into the capillary were investigated. The new system showed high separation ability and efficiency due to high specific surface area of nanomaterial and mixing separation mechanism. The transport equations of aromatic acids using the open-tubular electrochromatographic column with magnetic nanoparticle coating as stationary phases were derived under isocratic and double stepwise gradient elutions, and the retention characteristics of organic acids separated by the columns were further investigated. The results showed that the electroosmotic flow gradually decreased with the increase of Fe3O4@SiO2-NH2 in the mixed stationary phases, and the direction of electroosmotic flow reversed eventually. The capacity factor was relevant to the ratio of ion-exchange and reversed-phase stationary phases. Furthermore, experiments confirmed that the capacity factor of solute had a good linear relationship with the ratio of mixed stationary phases, and the correlation coefficient was greater than 0.9166 after fitting. Under the double stepwise gradient elution condition, the migration time of solute can be predicted by its elution time under isocratic elution. After the solutes were eluted by phosphate buffer stepwise gradient elution, the relative errors between predicted retention time and actual retention time of solute were less than 8.0%. After they were eluted by organic modifier concentration stepwise gradient elution, the relative errors between two values of solute were less than 10%. After they were eluted by pH value stepwise gradient elution, the relative errors between two val- ues of solute were less than 5.8%. Rhizoma gastrodiae was separated by the constructed system under the optimized chroma- tographic condition, the main components of gastrodin, vanilla alcohol and citric acid were identified based on retention time of standards, and the relative errors between predicted value and actual value of citric acid was 11%. The open-tubular elec- trochromatographic system shows great potential in the method development of analysis of complicated samples. Keywords gradient elution; transport characteristic; mixed stationary phase 1 引言

The characteristics of open-tubular capillary electrochromatography columns with series/mixed stationary phases constructed with magnetic nanoparticle coating

Novel open-tubular capillary electrochromatography (OT-CEC) systems with core/shell magnetic nanoparticles modified by amino or C18 groups as stationary phase were constructed by immobilizing nanoparticles in the capillary with permanent magnets. Influence of preparation method of OT-CEC column with series stationary phases (continuous two-dimension) on column performance and effect of dispersant on capability of OT-CEC column prepared by stationary phases with mixed functionalities (mixed stationary phases) were investigated in details to achieve stable preparation. Organic acids were used to evaluate the OT-CEC systems, and the relative column efficiency of salicylic acid was 420,000 plates/m for series stationary phases, while that of benzoic acid reached 480,000 plates/m for mixed stationary phases. The excellent within-column and between-column repeatability (n=5) testified with the RSDs of retention time were less than 0.44% and 10.20% for series stationary phases and 1.65% and 4.29% for mixed stationary phases. The two OT-CEC systems were further applied to separation of the aqueous extract of Rhizoma gastrodiae. Comparing with normal OT capillary column, the new systems show extra high column efficiency due to large surface areas of nanoparticles and multiple separation mechanisms, and they have great potential in the method development for the analysis of complicated samples.

SORPTION PROPERTIES OF THE MIXED STATIONARY PHASE ”POLYDIMETHYLSILOXANE-/beta-CYCLODEXTRIN” IN GAS CHROMATOGRAPHY

Sorption and selective properties of the mixed stationary phase based on polydimethylsiloxane and methylated-beta-cyclodextrin were studied by gas chromatographic method in the temperature range 60–180С. It is also established that introduction of macrocyclic adding in polymeric immovable phase results in increasing sorption of organic compounds of different classes (apart from n-alkanes C6-C10 and cyclogegsan) and showing of enantioselectivity, more pronounced for cyclic compounds with polar substituents. A greater role of entropy factors acting in the mixed polymer phase on the sorption of sorbates redistribution

Chemometric Study of Retention on Binary Stationary Phases in Gas Chromatography

Using gas chromatography, data analysis is performed on a dataset consisting of 486 retention indices, 27 standards (ramified alkanes, aliphatic alcohols, and aromatic compounds), 6 pure and binary stationary phases, and three temperatures. The behavior of the pure stationary phases (OV-3, OV-225, OV-61-OH, and OV-1701-OH) and the binary stationary phases (OV-3/OV-225 and OV-61-OH/OV-1701-OH) at different temperatures (60°C-100°C) is investigated with factor and topological analysis. The influence of temperature and the nature of the mixed stationary phases on the retention indices is studied by correspondence factor analysis (CFA). The non-additivity of the retention properties of the pure phases used as mixed phases is clearly established by CFA. The topological analysis of the substituent's effect is investigated with a DARC/PELCO procedure and shows the particular influence of the stationary phase composition on the retention. The substituent effect is measured for the pure and binary stationary phases at various temperatures. The evolution of the substituent effect from the pure stationary phases to the binary phases is discussed.

Chromatographic and adsorption properties of the mixed stationary phase poly(1-trimethylsilyl-1-propyne)/poly(1-phenyl-1-propyne)

Adsorption and chromatographic properties of the mixed stationary phase poly-(1-trimethylsilyl-1-propyne)/poly(1-phenyl-1-propyne) (PTMSP/PPP) composed as 97: 3 by weight have been investigated by methods of low-temperature nitrogen adsorption and gas chromatography on packed columns. The resultant phase has uniform mesoporous structure. The chromatographic properties of the mixed phase are significantly different from the properties of the original porous polymers PTMSP and PPP. The adsorbent obtained by modifying Chromosorb P NAW with a mixture of polymers provides the selective separation of chlorosubstituted, saturated, and aromatic hydrocarbons.

Ionic liquid‐bonded polysiloxane as stationary phase for capillary gas chromatography

Ionic liquid (IL) stationary phase is especially suitable for separation of complex samples, owing to the "dual nature" of IL. In this study, a synthetic method of ionic liquid-bonded polysiloxane (PSOIL) as stationary phase of GC was proposed. Then, the PSOIL was used to prepare an 8 m capillary column by static method. The column efficiency was measured to be about 4000 plates/m (k=3.55, naphthalene) after the column had been conditioned at 210°C. The durability of PSOIL column was better than that of the mixed stationary phase of IL and OV-1. Moreover, the Abraham solvation parameter model was employed to characterize the PSOIL. The result revealed that the PSOIL had stronger dispersion force (l) than neat IL and stronger hydrogen bond basicity (a) than DB-1. That meant the PSOIL might offer good selectivity for both polar and non-polar analytes. The column exhibited unique selectivity for various organic substances, such as the homologous compounds of alkanes, esters, alcohols and aromatic compounds. It was also found that some aromatic positional isomers could be separated better on the PSOIL column than on the DB-1 column. Furthermore, the stationary phase was suitable for separation of high-boiling point compounds such as polycyclic aromatic hydrocarbons, phthalic esters, etc. All of these demonstrated that the PSOIL offered good selectivity and high separation efficiency for a wide range of analytes.