Optimization of St John's Wort flavonoid separation by reversed phase liquid chromatography on a silica-based monolithic column

Summary An optimization procedure for the separation of flavonoids from St John's Wort by reversed-phase high-performance liquid chromatography on monolithic stationary phase is described. Three-component mobile phase systems are studied using experimental design methodology. The starting experimental domain is a triangle, each vertex of which is a pure component. From preliminary isocratic experiments, truncations in the domain are performed leading to a quadrilateral shape working domain with no symmetry. To cope with both separation and analysis time, desirability functions are used. Optimal conditions are finally given by binary systems and the four flavonoids are separated in less than seven minutes.     

高效液相色谱氮杂冠醚键合固定相的合成及性能研究

我们曾用γ－氯丙基键合硅胶（ＣＰＳ），在氢化钠（ＮａＨ）作用下合成了３－（氮杂－１８－冠－６）丙基键合固定相（ＢＣＰ）［１］．该固定相对碱基、核苷酸、硝基苯酚等有较好的分离选择性，但由于ＮａＨ对硅胶基质腐蚀作用较大，导致ＢＣＰ柱效及渗透性较低．本文采...     

一种包覆型聚合物高效液相色谱固定相的制备与评价

当代应用最广的HPLC固定相中,硅胶基质填料化学稳定性较低,并且由于残存硅羟基而表现所谓第二效应,特别使碱性化合物的峰形拖尾;聚合物基质填料虽提高了化学稳定性,没有离子基团,但刚性降低,并且由于溶胀难于进行梯度淋洗;面包覆型聚合物填料则可综合二者的优点,本文对我们制备的这种固定相作初步报道。     

Stationary queues with one autonomous server

Given a stationary stochastic continuous demand of service σ(θ_tω) dt with ∫ σ(ω)P(dω) < 1, we construct real stationary point processes $\text{(T}{}_{\mathrm{n}}\text{, n ∈}\text{Z}\text{)[T}{}_{\mathrm{n}}\text{< T}{}_{\mathrm{n}}\text{+1, lim}{}_{\mathrm{\pm \infty }}\text{T}{}_{\mathrm{n}}\text{= ±∞]}$ such that

for a given constant D \2>0. These point processes correspond to a service discipline for which a single server services during the time intervals [T_n, T_n+1[ the demand of service accumulated during the proceding intervals [T_n?1, T_n[ and take a rest of fixed duration D.     

One-Step Synthesis of Monolithic Silica Nanocomposites in Fused Silica Capillaries

The ideal way to prepare efficient, yet robust stationary phases for microanalytical high-resolution methods such as capillary chromatography and electrochromatography remains to be defined. In this contribution a one step sol-gel process is proposed for the production of monolithic, macroporous nanocomposite phases in fused silica capillaries, which require no additional derivatization, since they already bear the interactive (C8) moieties. The effect of the catalyst, the water content, the pH, as well as that of certain additives on monolith formation and porosity is investigated. Volume shrinkage and a tendency to crack were the major obstacles to overcome. Homogeneous stationary phases could be produced by applying a pH gradient during sol formation, thereby changing the catalytic principle from acidic (0.1 M HCl) to basic (gradual formation of OH^– as a consequence of the hydrolysis of N-methylformamide). Gelation/coacervation of suchgels could be induced by the addition of N,N-diethylamine. The water content during sol formation was determined as decisive for pore formation, with 250% of the amount theoretically needed for complete hydrolysis of all precursors giving optimal results. The volume shrinkage problem during xerogel formation was resolved by integrating dialkyldialkoxysilane units (dimethyldiethoxysilane 35 mol%) into the silica network.     

高效液相色谱法拆分雷喏嗪

用高效液相色谱法(HPLC)在正相条件下,用自制的涂敷直链淀粉-三(3,5-基苯基氨基甲酸酯)(ADMPC)手性固定相直接拆分了高效低毒的抗心绞痛药物雷喏嗪外消旋体(Ranolazine),并考察了二元及三元流动相体系对样品分离的影响,结果表明,三元流动相中的拆分结果远远好于二元流动相,流动相中不同种类醇改性剂及含量对样品保留时间和立体选择性有不同程度的影响．     

New stationary phases of conjugated π-electron systems for HPLC—characterization of structure and dynamics by solid state NMR spectroscopy

Four new stationary phases for HPLC were prepared by modifying silica gel with a trifrnctional aminoalkyl silane. A conjugated π-electron system was linked to the amino group either directly or with a carboxylic anhydride as a spacer in between. Characterization and dynamic measurements of the new stationary phases were performed by solid state NMR spectroscopy. The results of the ²⁹si and ¹³C CP/MAS techniques were compared with the recently developed ¹H MAS-only technique. Despite strong homonuclear dipole-dipole interactions it was possible to obtain well resolved ¹H MAS spectra of those stationaru phases with a high degree of crosslinking. Limited mobility of the aromatic ligand fragments is common for all examined stationaryu phases. The chromatographic properties of the new phases were tested by their ability tio sepatate a mixture of eight PAHS. It could be shown that the π-π interaction mechanism is responsible for the separation of the eight PAHs, because the elution order of the PAHs did not changem despite the use of both a nonpolar mobile phase (n-heptane) and a polar mobile phase (methanol/ water mixture).     

Analysis of the Association Process Between a Series of Phenol Derivatives with Two Novel Fluorinated Stationary Phase Using the Cl− Anion as Retention Marker

Summary Lithium chloride (LiCl) effect on the retention process of a phenol derivative series was investigated on two types of fluorinated stationary phase (i.e. a silica grafted with fluorinated linear alkyl chain (L-FSP) and a silica grafted with fluorinated aromatic ring stationary phase (A-FSP)). The results showed that the solute retention is enhanced when the A-FSP was used instead of the L-FSP due to additional – interactions. For the two fluorinated stationary phases (FSPs), the phenol-FSP association process can be divided into two LiCl concentration domains demonstrated that it was important to take into account the adsorbtion of Cl^– anion on the FSPs. As well, enthalpy-entropy compensation revealed that the solute retention mechanism was independent of the solute molecular structure and confirmed a change on the solute retention mechanism at a critical LiCl concentration value around 0.02M.     

一种非晶硅膜改性弹性玻璃毛细管交联中等极性固定相色谱柱的制备

研究了非晶硅膜改性的弹性玻璃毛细管交联ＯＶ－１７０１中等极性固定相色谱柱。在适当温度下，采用过氧化二异丙苯（ＤＣＵＰ）游离基引发交联ＯＶ－１７０１固定液，成功地制备了交联ＯＶ－１７０１柱，该柱具有柱效高、惰性好、耐溶剂、抗腐蚀和耐高温等性能，是一种新型高性能的中等极性交联柱。