RP-HPLC法丙交酯纯度的定量测定EI北大核心

建立了高效液相色谱(HPLC)测定丙交酯纯度的方法。解决了分析过程中丙交酯水解不稳定的问题。在HPLC分析过程中,无水的有机流动相不能实现丙交酯与其它杂质的分离,有机溶剂和水的混合溶液作流动相能有效改善丙交酯与其它杂质的分离效果。通过对实验条件的摸索,并对丙交酯水解动力学进行研究,发现丙交酯在选定的色谱条件下,在流动相中的水解反应具有准一级反应动力学的特征,由此可对丙交酯进行定量分析。实验表明,相对标准偏差RSD<1.0%,方法切实可行。     

气相色谱分析法在聚丙交酯合成中的应用

建立了用毛细管气相色谱法测定粗品丙交酯组分含量以及聚丙交酯中单体残留含量的方法。采用TP-5毛细管柱,以氢火焰离子化检测器检测,N2为载气,以校正面积归一化法计算粗品丙交酯中各组分的含量。在确定的色谱条件下,样品中各组分分离较好,分析周期仅为10 min;同时绘制丙交酯的标准曲线,测定了聚丙交酯中残留单体的含量,该方法可快速、准确地用于丙交酯的测定。     

HPLC法测定帕瑞昔布钠中有关物质的方法研究

建立以高效液相色谱法(HPLC)测定帕瑞昔布钠中有关物质的方法。色谱柱为C18柱(4.6 mm×250mm×5μm),乙腈-0.01 mol/L磷酸氢二钠溶液(用磷酸调节p H值至3.0)(47∶53,ν∶ν)为流动相,检测波长为215 nm,柱温40℃。经过优化色谱条件后,帕瑞昔布钠峰与6个已知杂质峰均可达到基线分离,样品主峰及各杂质的色谱峰的灵敏度和分离度均满足测定要求。采用HPLC法测定帕瑞昔布钠中的有关物质,专属性强,方法灵敏度高,结果准确可靠。     

对二氧环己酮与丙交酯共聚反应的~1H-NMR分析

由对二氧环己酮（PDO）和丙交酯（LA）单体,在不同温度下合成了PDO-co-LA共聚物,采用核磁共振（1H-NMR）研究了共聚反应动力学和共聚物分子链结构,提出了一种链段平均序列长度的计算方法。结果显示,丙交酯在共聚反应中的聚合能力要比对二氧环己酮强;实验条件下LA/PDO投料物质的量比为2/3时,共聚物中PDO与L...     

生物可吸收材料PDLLA的聚合条件研究

通过乳酸脱水合成出高纯度的D ,L 丙交酯。以辛酸亚锡为引发剂 ,进行丙交酯开环聚合为聚乳酸 (PDLLA)的实验研究。讨论了D ,L 丙交酯开环聚合的影响因素和PDLLA聚合条件     

乳酸钠催化合成丙交酯的研究

以乳酸钠为催化剂,研究了乳酸合成丙交酯过程中温度、压力、催化剂用量、脱水时间等因素对丙交酯产率的影响.用熔点测定仪和红外光谱仪对丙交酯进行了表征.对乳酸低聚物的形成和裂解作了分析.结果表明,乳酸钠具有良好催化效果,丙交酯初产率达81%,最佳反应条件分别是:催化剂用量1.5%,脱水阶段温度130℃、真空度-0.030MPa,脱水时间3h,裂解阶段应在230℃和-0.095MPa下反应3h.     

聚乳酸单体-丙交酯的合成

以D,L-乳酸为单体,无水氧化锌(ZnO)为催化剂,低真空条件下乳酸先缩聚后解聚制备了D,L-丙交酯.考察了脱水温度、脱水率、催化剂用量、解聚温度对丙交酯产率的影响.改进丙交酯的提纯方法,提高了丙交酯的重结晶收率.毛细管熔点法测定了产物的熔点,并用红外光谱、差示扫描量熟法、X-射线衍射分析对产物进行了分析表征.结果表明,所得产物为高纯的环状丙交酯.     

D,L-丙交酯的合成条件优化研究

制备了SO42-/Al2O3/La3 固体超强酸和辛酸亚锡复配作为丙交酯合成的催化剂.经多种催化剂的催化效率比较,进行多组实验发现该催化剂在较高反应压力下高产丙交酯的合成条件.结果表明,催化剂、反应温度、脱水时间等对丙交酯的产率有显著影响.     

精密而快速的色谱分析

超临界流体可以用做色谱的流动相，使混合物质在色谱柱上得到分离，这种分离方法被称为超临界流体色谱(Supercritical Fluid Chormatography，简称SFC)。与高效液相色谱(HPLC)相比，SFC一个显著的优点是分析／制备的快。     

单模聚焦微波作用下端炔基修饰的聚(L-丙交酯)的合成与表征

在单模聚焦微波辐射作用下,以辛酸亚锡为催化剂,炔丙醇为小分子引发剂引发L-丙交酯开环聚合合成了端炔基修饰的聚(L-丙交酯)。通过正交实验考察了各种反应条件对产物产率的影响,得出最佳的聚合反应条件如下:反应温度110℃,微波功率45W,辐照时间45min,催化剂用量0.1%。在此基础上,通过改变n(L-丙交酯)∶n(炔丙醇)投料比合成了一系列端炔基修饰的聚(L-丙交酯),通过FT-IR、1H NMR、DSC、XRD和GPC对其结构与性能进行了研究。结果表明,在微波作用下,快速、高效地合成了端炔基修饰的聚(L-丙交酯)目标产物,且产物的结构与性能可以通过改变n(L-丙交酯)∶n(炔丙醇)投料比在一定程度上进行调控,随着L-丙交酯投料量增大,产物的分子量逐渐增大,熔点逐渐升高。     

Effect of a variety of organic additives on retention and efficiency in micellar liquid chromatography

The effect of 21 organic additives (alkanols, alkane diols, dipolar aprotic solvents, alkanes) on the chromatographic behavior (retention, elution strength, efficiency) of probe solutes of widely differing hydrophobicity, such as benzene and 2-ethylanthraquinone, have been examined using a C18 stationary phase and sodium dodecyl sulfate (SDS) micellar mobile phases. The mobile-phase elution strength parallels the octanol-water partition coefficients of the additives or their ability to bind to the SDS micellar system, due to the increased solubility in the mobile phase and reduced affinity for the additive-modified surfactant-coated stationary phase. The comparison of the elution strength of micellar mobile phases with that of a reference acetonitrile-water system indicates that the elution strength is lower for micellar systems and depends on the nature of the eluted solute. The displacement of the solute-micelle and solute-stationary phase binding equilibria is quantified for several probe solutes eluted with micellar mobile phases in the presence of 1-propanol, 1-butanol, 1-pentanol, and acetonitrile. A correlation was also observed between the number of theoretical plates and the hydrophobicity of the alcohol additives: the efficiency initially increased steeply and reached a plateau. Compared to benzene, a more hydrophobic additive was needed to attain the maximum efficiency for the more hydrophobic 2-ethylanthraquinone analyte. Dipolar aprotic solvents appear to be somewhat more effective in enhancing the efficiency than alcohols. The results are rationalized in terms of the ability of the organic additives to alter the composition, structure, dynamics, and properties of the micelles and the surfactant-coated stationary phase.     

Chromatography with dynamically created liquid "stationary" phases: methanol and carbon dioxide

Liquid films composed of binary mixtures of carbon dioxide and methanol were created in empty capillary columns to produce effective stationary phases for chromatography. Under certain conditions of temperature, pressure, and stoichiometric composition, a binary mobile phase composed of CO2 and an organic liquid, such as methanol, can form two immiscible (gas and liquid) phases within a chromatographic column. The two phases can coexist in dynamic equilibrium with the liquid phase migrating through the column at a slower velocity than the gas phase. The liquid phase, composed of methanol saturated with carbon dioxide, acted as a chromatographic stationary phase while the gas phase, composed of carbon dioxide saturated with methanol, acted as a chromatographic mobile phase. The exact conditions necessary for the formation of two phase systems were determined from three-dimensional (P, T, XY) phase diagrams calculated from the Peng-Robinson cubic equation-of-state using one-parameter mixing rules. Separations of simple hydrocarbon mixtures are illustrated under various experimental conditions.     

Analysis of nicotine and its oxidation products in nicotine chewing gum by a molecularly imprinted solid-phase extraction

Chromatographic stationary phases showing exceptional selectivity for nicotine can be prepared by the technique of molecular imprinting. Such phases were used in the search for a rapid cleanup step for nicotine and some of its oxidation products in chewing gum formulations. Thus, using an organic mobile phase, the nicotine analytes from chewing gums dissolved in nonpolar solvent were retained, whereas the nonpolar matrix eluted close to the void peak. A subsequent switch to an acidic mobile phase resulted in elution of the analytes as one sharp peak. Due to weak binding of the less basic oxidation products, other imprinted polymers were tested, and the solid-phase extraction procedure was optimized. Polymers were prepared using various functional and cross-linking monomers, templates, porogens and thermal treatments. This resulted in phases that, when compared with a nonimprinted or a C18 reversed-phase column, showed significantly higher recoveries of the analytes. Furthermore, no bleeding of template from the phases could be detected. The cleanup step was coupled off-line to reversed-phase HPLC, and the efficiency of the analysis was compared with and without the cleanup step. Three out of four analytes were quantitatively recovered using the imprinted phase, whereas, using the nonimprinted phase, only nicotine was recovered. Without the cleanup step, none of the analytes could be determined using the reversed-phase HPLC method.     

Methylene Selectivity and Eluotropic Strength Variations in Subcritical Fluid Chromatography with Packed Columns and CO(2)-Modifier Mobile Phases

This work has consisted of better understanding the chro-matographic behavior in subcritical fluid chromatography with CO(2)-acetonitrile and CO(2)-methanol mobile phases. To that end, the changes of solute solubility in the mobile phase have been studied by determination of methylene selectivity of a homologous series. Moreover, eluotropic strengths have been calculated for mobile phases containing from 5 to 45% modifier. To carry out the studies in all ranges of the subcritical area, experimental designs have been used. The influences of analytical temperature (from 10 to 30 °C) and outlet pressure (from 10 to 20 MPa) have also been investigated both on solubility and on eluotropic strength. A more general comparison of elu-otropic strengths of subFC and HPLC has been achieved.     

Polar polymeric stationary phases for normal-phase HPLC based on monodisperse macroporous poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads

The effect of variables such as shape template size, porogen composition and percentage, content of cross-linking monomer, and polymerization temperature on the properties of uniformly sized 3-microm porous poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads prepared by the staged templated suspension polymerization technique has been studied. The porous properties of the beads including surface morphology, pore size distribution, and specific surface area have been optimized to obtain highly efficient stationary phases for normal-phase HPLC. A column packed with diol stationary phase obtained by hydrolysis of poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads affords an efficiency of 67,000 plates/m for toluene using THF as the mobile phase. The retention properties and selectivity of the diol beads are easily modulated by changes in the composition of the mobile phase. The performance of these beads is demonstrated with the separations of a variety of polar compounds including positional isomers, aniline derivatives, and basic tricyclic antidepressant drugs.     

Fluorous affinity chromatography for enrichment and determination of perfluoroalkyl substances

The adsorption behavior of four perfluoroalkyl acids, including the environmentally relevant perfluorooctanoic acid, has been investigated on a straight-chain perfluorohexyl adsorbent. The aim of this study was to probe the potential of perfluorinated materials for the analysis and enrichment of perfluoroalkyl analytes. Water/acetonitrile mixtures, to which formic acid had been added (generally, 0.1%), were employed as mobile phases. For all perfluorinated acids, a U-shaped retention profile was observed by changing the amount of acetonitrile in the mobile phase. This behavior has been correlated to the excess adsorption of the organic component on the adsorbent surface. The concept of perfluoromethylene selectivity has been defined as the ability of a chromatographic system to discriminate between molecules that differ by a single perfluoromethylene group. The contribution to the Gibbs free energy of phase transfer for the passage of a perfluoroalkyl carbon from the mobile to the stationary phase has been evaluated. This information, in addition to the traditional van't Hoff analysis, has also been used to estimate the analogous contribution for the transfer of a carboxylic unit. Finally, insights into the retention mechanisms of perfluoroalkyl acids on straight-chain perfluorohexyl sorbents are discussed.     

The use of deuterium oxide as a mobile phase for structural elucidation by HPLC/UV/ESI/MS

The use of deuterium oxide as a mobile phase in the routine analysis of pharmaceutical compounds was investigated. The deuterium exchange of labile hydrogen atoms aids in structural confirmation and elucidation of unknown impurities and degradation products. Although deuterium oxide as a mobile phase does in some cases change the retention times, the changes in retention times do not interfere with the analysis. A study of the high-performance liquid chromatography system shows that equilibration times for the deuterium-containing mobile phases are similar to equilibration times with changes of other mobile phases. The use of this technique in the analysis of pharmaceutical compounds and other small molecules is presented.     

Retention mechanism of weak polar solutes in reversed phase liquid chromatography

The retention mechanism of a weak polar solute, a series of 10 benzodiazepines in reversed phase liquid chromatography, was investigated over a wide range of mobile phase compositions. The values of enthalpy (ΔH°) and entropy (ΔS°) of transfer from the mobile to the stationary phases were determined. The method studied each factor (water fraction Φ in the acetonitrile (ACN)/water mixture and column temperature) controlling the retention mechanism. The changes in ΔH° and ΔS° as a function of the water fraction Φ in the ACN/water mixture were examined. These variations are explained using the organization of organic modifier (ACN) in clusters in the ACN/water mixture. A change in the retention mechanism thus indicated when the ACN/water mixture was used instead of the hydrogen-bonded mobile phase such as CH(3)OH/water. Enthalpy-entropy compensation revealed that the retention mechanism was independent of the water fraction Φ but showed that differences between the molecular structures of the benzodiazepines contributed more significantly to changes in the retention process in the CH(3)OH/water mixture than in the ACN/water mixture.     

Feasibility of supercritical fluid chromatography/mass spectrometry of polypeptides with up to 40-mers

Supercritical fluid chromatography (SFC) provides a number of advantages over traditional HPLC such as speed, practical use of longer columns, a normal-phase retention mechanism, and reduced use of organic solvents. Yet, it has been a technique traditionally limited to relatively nonpolar compounds. The nature of SFC mobile and stationary phases did not allow the elution of ionic compounds or of peptides, except, in the latter case, for the most hydrophobic peptides. The characterization of peptides is critically important for drug discovery and development in the pharmaceutical industry, as well as for a variety of other important applications. Here, for the first time to our knowledge, we show that relatively large peptides (at least 40 mers), containing a variety of acidic and basic residues, can be eluted in SFC. We used trifluoroacetic acid as additive in a CO2/methanol mobile phase to suppress deprotonation of peptide carboxylic acid groups and to protonate peptide amino groups. A 2-ethylpyridine bonded silica column, which was specifically developed for SFC, was used for the majority of this work. The relatively simple mobile phase was compatible with mass spectrometric detection.     

The effect of stationary-phase pore size on retention behavior in micellar liquid chromatography

One of the limitations that has restricted the applicability of micellar liquid chromatography (MLC) is the weak eluting power of micellar mobile phases compared to conventional hydro-organic mobile phases used in reversed-phase liquid chromatography. This may be the result of Donnan or steric exclusion of the micelles from the pores of the stationary phase, within which nearly all (> or = 99%) of the stationary phase resides and the analytes spend most of their time. To determine whether wide-pore stationary phases would overcome this limitation in MLC, several C8 and C18 stationary phases ranging from 100 to 4000 A were investigated using a diverse set of test solutes and micellar solutions of anionic, neutral, and cationic surfactants as mobile phases. With the larger pore size stationary phases, the eluting power of the MLC mobile phases was enhanced with all surfactant types, the greatest effect being with the neutral surfactant. Differences in retention behavior were observed between various solute types and between the C8 and C18 stationary phases. These differences appear to be related to the relative hydrophobicity of the solutes and to differences in the surfactant-modified stationary phases. Partitioning behavior of representative solutes on the large-pore C8 and C18 columns was shown to follow the three-phase partitioning model for MLC. Methylene group selectivity data showed only minor differences in the stationary-phase characteristics between the small- and large-pore size C18 columns. The true eluting power of micellar mobile phases was revealed with wide-pore stationary phases and was demonstrated by the separation and elution of an extended series of alkylphenones on C18 columns.