Polysiloxane-encapsulated stationary phase for reversed-phase high-performance liquid chromatography

Summary Silica beads of 6-μm average diameter were silanized with methylvinyldiethoxysilane and then subjected to encapsulation with poly(methylvinylsiloxane). The resulting product is a new stationary phase for reversed-phase high performance liquid chromatography (RP-HPLC) which has superior ability for the separation of polar, non-polar and basic compounds. The chromatographic peaks are symmetric. Its stability has been studied; after continuous use for three months the carbon content and chromatographic behaviour of the phase were unchanged. on to the silica surface to given an uniform organic film. Material prepared in this way has both good chromatographic behaviour and superior selectivity. Because contact of the silica matrix with the mobile phase is avoided, the alkali-resisting ability of the stationary phase is increased. The non-specific adsorption of alkaline solutes on to the silica surface is also avoided because of the complete coverage of surface silanol groups. Reports of stationary phases encapsulated with polystyrene [6], polybutadiene [I] and octadecylsiloxane polymers have recently appeared in the literature [3]. In this paper we report the encapsulation of poly-(methylvinylsiloxane) (analogous to the phase SE-31 often used in GC) on to a silica matrix previously modified with methylvinyldiethoxysilane. The resulting phase has superior performance in reversed-phase HPLC.     

Microwave-immobilized polybutadiene stationary phase for reversed-phase high-performance liquid chromatography

Polybutadiene (PBD) has been immobilized on high-performance liquid chromatography (HPLC) silica by microwave radiation at various power levels (52-663 W) and actuation times (3-60 min). Columns prepared from these reversed-phase HPLC materials, as well as from similar non-irradiated materials, were tested with standard sample mixtures and characterized by elemental analysis (%C) and infrared spectroscopy. A microwave irradiation of 20 min at 663 W gives a layer of immobilized PBD that presented good performance. Longer irradiation times give thicker immobilized layers having less favorable chromatographic properties.     

Novel imidazolium stationary phase for high-performance liquid chromatography

A new imidazolium anion-exchange phase immobilized on silica is synthesized. HPLC separations of common inorganic anions (IO3-, Cl-, NO2-, Br-, NO3-, I-, SCN-) have been performed using a HPLC column (200 mm x 4.6 mm I.D.) packed with this stationary phase, with a phosphate buffer solution as the mobile phase and UV detection at 200 nm. The effects of pH and concentration of eluent on the separation of anions have been studied. Chromatographic parameters are calculated and the results show that the new stationary phase is of significant potential for the analysis of these anions. Successful separations of some ordinary organic anions have also been achieved with the said stationary phase. Meaningfully, organic and inorganic anions can be determined simultaneously and satisfactorily with several neutral compounds using the column. The separation of some organic compounds including hydroxybenzenes, bases and amines by this stationary phase with only water as the eluent has been investigated.     

Poly(2-N-carbazolylethyl acrylate)-modified silica as a new polymeric stationary phase for reversed-phase high-performance liquid chromatography

Poly(2-N-carbazolylethyl acrylate) having terminal trimethoxysilyl groups was newly synthesized by radical polymerization and immobilized onto the silica surface (Sil-CEA). The chromatographic property of Sil-CEA was examined by applying polycyclic aromatic hydrocarbons as solutes. Poly(4-vinylpyridine)-modified silica (Sil-VP) and monomeric octadecylated silica (ODS) columns were used as the reference columns. Less sensitivity to molecular hydrophobicity and enhanced molecular planarity selectivity were obtained with Sil-CEA compared to ODS. On the other hand, high retention factors for the analyzed solutes and an opposite elution order for linear and disc-shaped solutes were obtained with Sil-CEA compared with Sil-VP. In this paper, the application for separation of tocopherols was also described.     

Separation of positional isomers of mono-poly(ethylene glycol)-modified octreotides by reversed-phase high-performance liquid chromatography

The purpose of this study was to develop a reversed-phase high-performance liquid chromatographic method (RP-HPLC) for separating each positional isomer from low- to high-molecular-weight mono-PEGylated octreotides prepared by polyethylene glycol (PEG) derivatives with various molecular weights (2, 5, or 20 kDa). In the gradient elution using acetonitrile and 10 mM phosphate buffer at pH 7.0 on a Phenomenex Gemini C-18 column (250 mm × 4.6 mm id, 5 μm), each positional isomer of the mono-PEGylated octreotides was completely resolved with good resolution (PEG-2K: 7.6, PEG-5K: 6.6, and PEG-20K: 3.1). The optimal RP-HPLC condition also resolved the degradation products of mono-PEG-octreotide isomers in thermal stability studies at 55 °C and enzymatic stability studies with trypsin. In conclusion, the developed RP-HPLC method will be valuable for studying the effect of PEGylation site and the attached PEG size on the physicochemical and pharmacological properties of PEGylated octreotides.     

Determination of poly(ethylene glycol)s by both normal-phase and reversed-phase modes of high-performance liquid chromatography

A normal-phase HPLC system using an amino column has been developed to characterise oligomers of poly(ethylene glycol)s (PEGs) of average M_r 400 to 2000 with derivatisation by dinitrobenzoate. Normal-phase HPLC with gradient elution using ternary solvents of hexane, dichloromethane and methanol has produced a baseline resolution for oligomers of PEG 400, 600 and 1000, while PEG 1000 and 2000 were analysed by using binary solvents of acetonitrile and water. Mixtures of PEGs have been determined by these HPLC systems. PEG 400 in a textile finish has also been determined with satisfactory recovery. It has been found that the hydroxyl group of solvents in normal-phase HPLC plays an important role in resolution and retention of PEG oligomers. Derivatisation efficiency for PEGs by dinitrobenzoyl chloride and quantitative determination of derivatised PEGs by HPLC have been studied. A reversed-phase (RP) mode of HPLC was examined for determination of PEG 400 oligomers. The normal-phase system provided greater resolution for oligomers of PEGs.     

新型吡咯烷键合反相高效液相色谱固定相的制备与研究（英文）

正A new ionic liquid-based high-performance liquid chromatography stationary phase is reported.A derivative of N-methyl pyrrolidinium tetrafluoroborate was covalently immobilized on the surface of silica particles to prepare silica-based N-methyl pyrrolidinium tetrafluoroborate(SilprMP BF4)stationary phase.The obtained ionic liquid-modified silica was evaluated and confirmed by elemental analysis,infrared spectroscopy,and thermogravimetric analysis.A column was packed with the modified particles.The retention behavior of aromatic compounds,alkyl benzenes,and acidic and basic compounds on the SilprMP BF4 stationary phase was studied under reversed-phase liquid chromatography conditions.The effect of the eluent pH on the separation of the acidic and basic compounds was also studied.The new stationary phase involves multiple retention mechanisms,such as electrostatic,hydrophobic,ion-dipole,and anion-exchange interactions,which might lead to multipurpose separation media.     

New poly(ionic liquid)-grafted silica multi-mode stationary phase for anion-exchange/reversed-phase/hydrophilic interaction liquid chromatography

A new poly(ionic liquid)-grafted silica stationary phase was prepared and characterized. It was then applied for multi-mode chromatographies, including ion-exchange, reversed-phase, and hydrophilic interaction liquid chromatographies for the effective separation of anions, hydrophobic compounds, and small polar molecules, respectively.     

Quinolinium ionic liquid-modified silica as a novel stationary phase for high-performance liquid chromatography

A novel stationary phase based on quinolinium ionic liquid-modified silica was prepared and evaluated for high-performance liquid chromatography. The stationary phase was investigated via normal-phase (NP), reversed-phase (RP), and anion-exchange (AE) chromatographic modes, respectively. Polycyclic aromatic hydrocarbons, phthalates, parabens, phenols, anilines, and inorganic anions were used as model analytes in chromatographic separation. Using the newly established column, organic compounds were separated successfully by both NP and RP modes, and inorganic anions were also separated completely by AE mode. The obtained results indicated that the stationary phase could be applied in different chromatographic modes, with multiple-interaction mechanism including van der Waals forces (dipole–dipole, dipole–induced dipole interactions), hydrophobic, π–π stacking, electrostatic forces, hydrogen bonding, anion-exchange interactions, and so on. The column packed with the stationary phase was applied to analyze phthalates and parabens in hexane extracts of plastics. Tap water and bottled water were also analyzed by the column, and nitrate was detected as 20.1 and 13.8 mg L^?1, respectively. The results illustrated that the stationary phase was potential in practical applications.

Determination of poly(ethylene glycol) 300 in long chain free fatty acid mixtures by reversed-phase high-performance liquid chromatography

A rapid sensitive method has been developed for the detection and quantitation of poly(ethylene glycol) 300 (PEG 300) in long-chain free fatty acid mixtures that requires minimal sample preparation. The PEG 300 was separated from the free fatty acids by RP-HPLC using a water–tetrahydrofuran gradient. PEG and the free fatty acids were detected using evaporative light scattering detection. The minimum detectable level of PEG in a free fatty acid mixture was 0.0125%.     

Development of some stationary phases for reversed-phase high-performance liquid chromatography

The availability of a variety of stable organic stationary phases for columns has been a key factor in the development of HPLC as a major scientific tool. This paper explores the history and rationale used in the development of some important stationary phases and attempts to identify some of the strengths and limitations of these materials. Some of the author's experiences in stationary phase development illustrate approaches leading to present-day columns that exhibit a broad range of selectivity coupled with a high degree of reproducibility. Suggestions also are made for additional stationary phases that may be needed to complete column selectivity potential for HPLC separations.     

Determination of iodide in seawater and edible salt by microcolumn liquid chromatography with poly(ethylene glycol) stationary phase

An ion chromatography method for rapid and direct determination of iodide in seawater and edible salt is reported. Separation was achieved using a laboratory-made C30 packed column (100 mm x 0.32 mm i.d.) modified with poly(ethylene glycol) (PEG). Effects of eluent composition on retention behavior of inorganic anions have been investigated. Both cation and anion of the eluent affected the retention of analyte anions. The retention time of anions increased with increasing eluent concentration when lithium chloride, sodium chloride, potassium chloride, sodium sulfate, magnesium sulfate were used as the eluent, while it decreased with increasing eluent concentration when ammonium sulfate was used as the eluent. The detection limit for iodide obtained by injecting 0.2 microl of sample was 9 microg/l (S/N = 3). The present method was successfully applied to the rapid and direct determination of iodide in seawater and edible salt samples. Partition may be involved in the present separation mode.     

Poly(1-allylimidazole)-grafted silica,a new specific stationary phase for reversed-phase and anion-exchange liquid chromatography

A new specific stationary phase based on poly(1-allylimidazole)-grafted silica has been synthesized and characterized, by infrared spectra, elemental analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. The results of test showed that poly(1-allylimidazole) can effectively mask the residual silanol groups and reduce the adverse effect of residual silanol. Using this stationary phase, phenol compounds, aniline compounds, and polycyclic aromatic hydrocarbons were successfully separated with symmetric peak shapes in the reversed-phase chromatography. Inorganic anions (IO₃⁻, BrO₃⁻, Br⁻, NO₃⁻, I⁻, SCN⁻) were also separated completely in the anion-exchange chromatography using sodium chloride solution as the mobile phase. The effects of pH and the concentration of eluent on the separation of inorganic anions were studied. The separation mechanism appears to involve the mixed interactions of hydrogen bonding, hydrophobic, π–π, electrostatic, and anion-exchange interactions.     

Synthesis and characterization of novel polar-embedded silica stationary phases for use in reversed-phase high-performance liquid chromatography

We have developed a series of new C₁₀ dipeptide stationary phases via a simple and effective synthetic method. The preparation of the new phases involves the synthesis of silanes and the surface modification of silica. Chromatographic evaluations of these columns were performed using the Engelhardt, Tanaka, and Neue test mixtures. The applicability of these new stationary phases was also evaluated using a series of diagnostic probes including acids, bases or neutral compounds and several generic applications. These new C₁₀ dipeptide stationary phases showed excellent hydrolytic stability over a wide pH range. Like other existing amide-embedded columns, these new stationary phases exhibit higher retention for polar and hydrophilic compounds and different selectivity as compared to conventional C₁₈ columns. These new phases are compatible with 100% aqueous mobile phases, and also provide high column efficiency and good peak shapes for both acidic and basic compounds.     

Column packing for gas chromatography containing immobilized poly(ethylene glycol) stationary phase

Summary Carbowax 20M poly(ethylene glycol) stationary phase was immobilized on Chromosorb W by cross-linking with pluriisocyanate. The properties of the prepared packing material were investigated. Column efficiencies of 10,960 and 7,510 theoretical plates/meter were obtained for n-pentadecane and 1-heptanol, respectively.     

N-Methylimidazolium anion-exchange stationary phase for high-performance liquid chromatography

In this paper, the preparation of a new anion-exchange phase based on N-methylimidazolium immobilized on silica is described. HPLC separations of common inorganic anions, including an iodate, chloride, bromide, nitrate, iodide, and thiocyanate, were performed using a HPLC column (200 x 4.6mm I.D.) packed with the said phase, and phosphate buffer solution and acetate buffer solution as the mobile phases respectively, with UV detection at 200 nm. The effects of pH and the concentration of the eluent on the separation of anions were studied. With the efficiency and resolution of the column calculated, the results showed that this new phase can be used in the analysis of these in organic anions with great prospects. At the same time, successful separations of some organic anions, amines and nucleotides have also been obtained respectively using this new phase. The phase displayed a main strong anion-exchange mechanism and a coexistent reverse-phase interaction, etc.     

Preparation of a polybutadiene stationary phase immobilized by gamma radiation for reversed-phase high-performance liquid chromatography

Polybutadiene (PBD) has been immobilized on HPLC silica by gamma radiation doses in the range from 5 to 180 kGy. Columns prepared from these reversed-phase materials, as well as from similar non-irradiated materials, were tested with standard sample mixtures and characterized by elemental analysis (% C) and infrared spectroscopy. A low dose of 5 kGy is sufficient to produce a layer of immobilized PBD which functions as an efficient and stable stationary phase. Higher doses give thicker immobilized layers having less favorable chromatographic properties.     

Preparation and characterization of a magnesia-zirconia stationary phase modified with β-cyclodextrin for reversed-phase high-performance liquid chromatography

A new stationary phase of magnesia-zirconia composite matrix for high-performance liquid chromatography was first prepared by modification of β-cyclodextrin (β-CD) via fosfomycin as a spacer. Various modification procedures were attempted for achievement of successful modification. The modified composite was characterized by using coloration, elemental analysis, diffused reflectance FT-IR, surface area and pore size distribution. The separation of alkylbenzenes, polycyclic aromatic hydrocarbons, positional isomers of some acidic, basic and amphoteric disubstituted benzenes was studied on the new stationary phase. The effect of pH and methanol content in the mobile phase on retention and separation selectivity for the positional isomers were investigated. The chromatographic performance of CD modified magnesia-zirconia was compared with fosfomycin modified magnesia-zirconia as intermediate material and bare magnesia-zirconia as raw material. The results show that various retention mechanisms such as hydrophobicity, inclusion complexation and hydrogen bond interaction exist in the chromatography process of the packing modified with CD. The β-CD played the major role in the chromatographic property of this new stationary phase. The modified magnesia-zirconia exhibits superiority of separation for basic aromatics and high stability above pH 11.