Stability studies of stationary phases from poly(methyltetradecylsiloxane) sorbed and immobilized onto metalized and unmodified silicas

Stationary phases for RP-HPLC were prepared from metalized (titanized and zirconized) and unmodified silica particles using sorbed and immobilized poly(methyltetradecylsiloxane) (PMTDS). Different immobilization procedures, such as gamma irradiation and thermal treatments, were used for the preparation of the immobilized PMTDS phases. The stabilities of these stationary phases were evaluated by passing alkaline (pH 10) mobile phase through 60 mm x 3.9 mm columns of the different phases, with periodic tests to evaluate chromatographic performance. The results show that higher stabilities were obtained with stationary phases based on PMTDS immobilized on zirconized silica, these phases being 50% more stable than their titanized silica counterparts and 400% more stable than those based on unmodified silica. These supports provide higher chemical stability to the laboratory-made stationary phases, when compared with chemically bonded silica-based phases.     

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.     

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.     

Preparation and characterisation of anion-exchange latex-coated silica monoliths for capillary electrochromatography

Silica monoliths coated with functionalised latex particles have been prepared for use in monolithic ion-exchange capillary electrochromatography (IE-CEC) for the separation of inorganic anions. The ion-exchange monoliths were prepared using 70 nm quaternary ammonium, anion-exchange latex particles, which were bound electrostatically to a monolithic silica skeleton synthesised in a fused silica capillary. The resulting stationary phases were characterised in terms of their chromatographic performance and capacity. The capacity of a 50 microm diameter 25 cm latex-coated silica monolith was found to be 0.342 nanoequivalents and 80,000 theoretical plates per column were typically achieved for weakly retained anions, with lower efficiency being observed for analytes exhibiting strong ion-exchange interaction with the stationary phase. The electroosmotic flow (EOF) was reversed after the latex-coating was applied (-25.96 m2 V(-1) s(-1), relative standard deviation (RSD) 2.8%) and resulted in anions being separated in the co-EOF mode. Ion-exchange interactions between the analytes and the stationary phase were manipulated by varying the ion-exchange selectivity coefficient and the concentration of a competing ion (phosphate or perchlorate) present in the electrolyte. Large concentrations of competing ion (greater than 1M phosphate or 200 mM perchlorate) were required to completely suppress ion-exchange interactions, which highlighted the significant retention effects that could be achieved using monolithic columns compared to open tubular columns, without the problems associated with particle-packed columns. The latex-coated silica monoliths were easily produced in bulk quantities and performed reproducibly in acidic electrolytes. The high permeability and beneficial phase ratio makes these columns ideal for micro-LC and preconcentration applications.     

聚合反应制备键合型纤维素-三(4-甲基苯基甲酸酯)衍生物类手性固定相

合成了带有甲基丙烯酰基的纤维素-三(4-甲基苯基甲酸酯)衍生物(CTMB),并通过聚合反应将其键合在具有双键的硅胶表面,得到手性固定相(CSP)。用所得到的CSP对9种对映体化合物(丁苯酞、酮基布洛芬、反-2,3-二苯环氧乙烷、安息香、安息香类似物、托葛尔碱、华法令、4,4′-二甲氧基-5,6,5′,6′-二次甲二氧基-2,2′-羰甲基甲酯联苯、4,4′-二甲氧基-5,6,5′,6′-二次甲二氧基-2-羰甲基甲酯-2′-羰甲基乙酯联苯)进行了拆分。考察了CSP制备过程中甲基丙烯酰氯的用量、键合方式以及硅胶     

手性选择体的固定量对固定相手性分离的影响

为研究手性选择体的固定量对固定相对映体分离能力的影响,将L-(-)-二苯甲酰酒石酸与苯甲醇反应,制备出单苄酯,再将此单苄酯的另一羧基转化为酰氯,得到手性选择体,将此选择体固定在氨丙基硅胶上,制备出选择体固定量较高的固定相,比较了此固定相与前期工作中选择体相同但选择体固定量较低的固定相在手性分离能力方面的差异,此外讨论了...     

Titania-based stationary phase in separation of ondansetron and its related compounds

Improvements in stationary phase stability have been and remain a great task for research of new stationary phases. Metal oxide-based stationary phases appear as one of perspective alternatives to classical silica based stationary phases regarding to their similar effectiveness, different selectivity, different retention mechanism and mainly better chemical and thermal stability. In this study, the retention behaviour of ondansetron and its five pharmacopoeial impurities on TiO(2)-based reversed phase was investigated. The influence of buffer type, pH and concentration on retention was studied. Different types and amount of organic solvent in mobile phase were tested. The effect of temperature and flow rate on separation was investigated. The separation conditions were optimized and developed method validated. The retention parameters - retention time (t(R)), retention factor (k'), theoretical plate number (N), resolution between peaks due to nearby peaks (R(s)) and symmetry factor (A(s)) have been compared to parameters achieved on polybutadiene-coated zirconia column. The thermodynamic parameters of retention of analysed compounds - enthalpy, entropy and Gibbs free energy - were calculated and compared to those achieved on polybutadiene-coated zirconia column. This work proves similarity of retention behaviour of ondansetron and its five related compounds on zirconia-based and titania-based stationary phases and potential utilisation of polyethylene covered TiO(2)-based reversed stationary phase as an alternative to polybutadiene-coated ZrO(2) stationary phase in pharmaceutical analysis of ondansetron.     

Application of diaza-18-crown-6-capped beta-cyclodextrin bonded silica particles as chiral stationary phases for ultrahigh pressure capillary liquid chromatography

Two bonded chiral stationary phases (CSPs), 8-aminoquinoline-2-ylmethyl- and 8-aminoquinoline-7-ylmethyl-diaza-18-crown-6-capped [3-(2-O-beta-cyclodextrin)-2-hydroxypropoxy]propylsilyl silica particles (non-porous, 1.5 microm), have been prepared and evaluated using capillary liquid chromatography at high pressures (> or = 8000 p.s.i.). High column efficiency (up to 400 000 plates m(-1)) was achieved for chiral separations. These CSPs with two recognition sites, i.e. substituted-diaza-18-crown-6 and beta-cyclodextrin combined with high chromatographic efficiency provide good resolution of a variety of enantiomers and positional isomers in relatively short times under reversed-phase conditions. After inclusion of a Ni (II) ion from the mobile phase, the positively charged crown ether-capped beta-cyclodextrin facilitates specific static, dipolar, and host-guest complexation interactions with solutes.     

Immobilized metallacarborane as a new type of stationary phase for high performance liquid chromatography

A new type of high performance liquid chromatography (HPLC) stationary phase was prepared, and its chromatographic properties were evaluated. The sorbent was composed of metallacarborane covalently bound to silica. Because of the chemical structure of the immobilized metallacarborane, the synthesized stationary phase was able to interact with nonpolar analytes via hydrophobic interactions. The chromatographic behavior of several low-molecular-weight hydrocarbons on the sorbent under typical reversed-phase conditions was compared with octadecyl-, sulfo phenyl- and aminopropyl-modified silica stationary phases. Moreover, as a consequence of the synthetic protocol employed, the immobilization of the metallacarborane led to the development of a zwitterionic chemically bonded phase, which demonstrated excellent resistance to "phase collapse" in a 100% aqueous environment. Finally, preliminary experiments indicated that the new stationary phase has the potential for utilization in hydrophilic interaction chromatography (HILIC) mode for the separation of polar compounds.     

Immobilized stationary phase on the basis of polyethylene glycol cross-linked with pluriisocyanates of the Desmodur type

Summary The preparation of an immobilized stationary phase based on Carbowax 20M is described. The stationary phase cross-linking was carried out with Desmodur N 75 or Desmodur L 75, pluriisocyanates. The properties of the prepared stationary phases are compared.     

New stationary phases for high-performance liquid chromatography based on poly(methyltetradecylsiloxane) thermally immobilized onto zirconized silica

The modification of silica with zirconium oxide followed by sorption and thermal immobilization of poly(methyltetradecylsiloxane) (PMTDS) is used to prepare a reversed stationary phase for high-performance liquid chromatography. The thermal immobilization of PMTDS on zirconized silica was optimized using a central composite design. The new stationary phase was characterized by spectroscopic and chromatographic methods. Stationary phases with good reproducibility and good chromatographic performance for various compounds were obtained. PMTDS thermally immobilized on zirconized silica presented quite significant chemical stability at pH 10 and 50 degrees C.     

Polysiloxane deactivated fused silica capillaries containing immobilized stationary phases

This article describes a method of preparing immobilized stationary phases which has arisen from the authors' work on polysiloxane deactivation of fused silica capillaries. Although acid treatment is often omitted with fused silica capillaries, there are good reasons for hydrothermal treatment of this column material. Use of Grob's peroxide method gave immobilized 0.25 μm films of SE-54; lowering of the immobilization temperature permitted immobilization of 0.1 μm films of the same phase.     

Facile synthesis of high-density poly(octadecyl acrylate)-grafted silica for reversed-phase high-performance liquid chromatography by surface-initiated atom transfer radical polymerization

To introduce high-density polymeric organic phase onto silica, initiator-modified silica was prepared and then surface-initiated atom transfer radical polymerization (ATRP) ("grafting-from" method) was carried out with octadecyl acrylate. The resultant polymer-grafted silica was characterized by diffuse reflectance infrared Fourier transform, suspension-state (1)H NMR, solid-state (13)C cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS-NMR), solid-state (29)Si-CP-MAS-NMR spectroscopies, elemental analysis and differential scanning calorimetry measurements. ATRP-based poly(octadecyl acrylate)-grafted silica (Sil-ODA(n)-1), was used as a stationary phase in high-performance liquid chromatography (HPLC) and the chromatographic behavior was evaluated by the retention studies of polycyclic aromatic hydrocarbons (PAHs) and aromatic positional isomers. Compared with previous poly(octadecyl acrylate)-grafted silica (Sil-ODA(n)), which was prepared by the "grafting-to" method, we have observed longer retention and greater selectivity for Sil-ODA(n)-1 towards PAHs event at higher temperature.     

Preparation and evaluation of a deoxycholic‐calix[4]arene hybrid‐type receptor as a chiral stationary phase for HPLC

We report the synthesis and enantioseparation characteristics of two novel covalently immobilized deoxycholic acid derivatives as chiral stationary phases for high‐performance liquid chromatography. In the structure of the first stationary phase, the 3‐position of deoxycholic acid is substituted with a 3,5‐dinitrophenylcarbamoyl group and the second one has an additional calix[4]arene attached to the carboxylic group of the deoxycholic acid. The chromatographic performance of the stationary phases was evaluated with enantioseparation of N‐(3,5‐dinitrobenzoyl)‐dl ‐leucine, N‐(3,5‐dinitrobenzoyl)‐dl ‐valine, omeprazole, diclofop‐methyl, dl ‐mandelic acid and (RS)‐pregabalin. Comparison of the performance characteristics of the prepared chiral stationary phases provided evidence for the active involvement of the calix[4]arene unit in the chiral recognition process. Both stationary phases are chemically bonded to the silica and can be used in both normal‐phase and reversed‐phase modes.     

Preparation and evaluation of a chiral HPLC stationary phase based on cone calix[4]arene functionalized at the upper rim with l‐alanine units

Here we report a new chiral stationary phase (CSP) immobilized on silica gel based on cone calix[4]arene functionalized at the upper rim with two l ‐alanine units as new chiral selector that has been used in high‐performance liquid chromatography. The CSP was prepared by covalently bonding the allyl groups at the lower rim of calix[4]arene to silica gel by thiol‐ene click chemistry reaction. Elemental analysis of the CSP showed that 120 μmol of chiral selector bonded per gram of silica gel. 1‐Hexene was used for end‐capping of unreacted mercapto groups on silica gel. Since the CSP is chemically bonded to the silica, it can be used in the normal‐phase and reversed‐phase mode and with halogenated solvents as mobile phases, if desired. The chromatographic performance of the CSP was evaluated in the enantioseparation of the 3,5‐dinitrobenzoyl derivatives of some amino acids, diclofop‐methyl and dl ‐mandelic acid.     

环果糖色谱柱分离4组结构类似物

考察了聚苯乙烯键合天然环果糖色谱柱MCI Gel CRS100、硅胶键合天然环果糖色谱柱Frulic N、硅胶键合异丙基氨基甲酸酯衍生环果糖色谱柱Larihc P、硅胶键合R-萘乙基氨基甲酸酯衍生环果糖色谱柱Larihc RN在正相模式下对免疫抑制剂、维生素E、姜黄类化合物、辣椒碱4组结构类似物的分离能力。考察了固定相支撑物、固定相功能基团、流动相组成等条件对色谱分离效率的影响。结果显示MCI Gel CRS100由于其固定相较强的疏水性适用于正相色谱而不适用于亲水作用色谱。衍生化的环果糖色谱柱Larihc P和Larihc RN比天然环果糖色谱柱Frulic N具有更高的选择性。三氟乙酸的加入对环果糖色谱柱在正相色谱中分离能力的影响较小。     

Preparation and characterization of poly(methyltetradecylsiloxane) stationary phases immobilized by gamma radiation onto zirconized silica

The preparation of stationary phases with enhanced chemical stability in alkaline eluents has been the principal objective of many chromatographers. New and improved silica substrates and advanced chemical modification methods are among the possibilities being investigated to reach this objective. The present work has evaluated these two possibilities for new stationary phases. First, the silica surface was modified by reaction with zirconium tetrabutoxide to produce zirconized silica particles having about 21% (w/w) of zirconium. Then poly(methyltetradecylsiloxane) (PMTDS) was immobilized onto this surface using different doses (50-120 kGy) of gamma radiation. These new phases were characterized using elemental analysis and infrared and solid-state (29)Si-nuclear magnetic resonance (NMR) spectroscopies. These new stationary phases presented column efficiencies of about 68,000 plates m(-1), symmetric peaks for apolar compounds and retention factors that depend on the irradiation dose and show improved stability in high pH mobile phases. The separation of several pharmaceuticals at pH 11 is presented.     

新型键合纤维素手性固定相的制备及其拆分性能评价

键合型多糖手性固定相因具有化学稳定性高和溶剂耐受性好的特点而受到研究者的极大关注。采用施陶丁格（Staudinger）反应将6-叠氮-6-脱氧纤维素-3,5-二氯苯基氨基甲酸酯键合到氨丙基硅胶上得到一种新的键合型手性固定相（ImCel）,研究了其手性分离性能,并探讨了非常规流动相（如氯仿、四氢呋喃等）的影响。结果表明,在20对手性化合物中,17对在合适的流动相下得到基线分离。ImCel在正相条件下的分离性能优于反相条件,且在含氯仿的流动相中仍对手性化合物表现出良好的分离能力。在分离一系列芴甲氧羰基（fmoc）-氨基酸衍生物时,ImCel与键合6-叠氮-6-脱氧纤维素-3,5-二甲基苯基氨基甲酸酯的手性固定相表现出互补性,出现了固定相改变引起的对映体洗脱反转现象。本研究丰富了键合型多糖手性固定相的种类和合成方法,为开发新的键合型手性固定相提供了参考。     

Some new selective stationary phases for RP-HPLC

At the present time, more complex analyses of apolar compounds with similar chemical structures or of polar compounds, especially basic ones, having diverse properties require more selective stationary phases having better stabilities. This paper describes several new stationary phases with directed selectivities that were prepared by immobilizing two different phenyl group-containing siloxanes and a trifluoropropyl-containing siloxane onto chromatographic silica and, in the case of the fluorinated siloxane, onto zirconized silica, using thermal treatment or microware radiation. The chromatographic properties and stabilities of these new phases were determined and several applications were evaluated. The phenyl-containing phases showed excellent characteristics related to the separation of several different types of aromatic compounds while the fluorinated phases, which present a more polar character, revealed selectivity for the separation of positional isomers as well as for a mixture of basic pharmaceuticals. Stability tests indicate that immobilization of the polysiloxanes increases column lifetimes by making the stationary phases less susceptible to dissolution, while the phases immobilized with microwave radiation were somewhat more stable than those immobilized by thermal treatments.     

1 μm硅胶颗粒固定相的加压电色谱分离性能

制备了1 μm无孔硅胶颗粒。通过电动填充法得到总长度为45 cm(固定相填充长度为20 cm)、内径为100 μm的毛细管色谱柱。以乙腈-水体系作为流动相,详细考察了碱性化合物在该色谱柱上的加压电色谱(pCEC)分离性能,讨论了流动相比例、缓冲液浓度、pH值及操作电压等因素对分离的影响。实验结果表明,裸硅胶柱在乙腈-水体系分离碱性样品中表现出典型的反相色谱分离性能;缓冲液浓度的改变则对分离影响不大。当pH值改变时,碱性化合物的解离程度发生变化,它们与固定相之间的作用力发生变化,使得分离度发生相应的变化。分离柱效随施加电压的增加而增加,在1 kV电压下,裸硅胶柱对邻甲苯胺的柱效为35000理论塔板/m。