微乳电动色谱法的研究进展

微乳电动色谱(MEEKC)是一种以微乳为背景电解质,以电压为驱动力的分离技术。本文对MEEKC中的各调节参数进行了概述,重点归纳了MEEKC法在正辛醇-水分配系数测定、中药和手性化合物分离方面的应用,以及在操作技术上的新进展,如多路进样技术以及在线联用质谱检测技术等,并通过对相关文献的分析,对一直存有争议的MEEKC与胶束电动色谱(MEKC)的联系与区别进行了讨论,最后提出了MEEKC法未来的发展空间。     

微乳液相色谱测定药物的油-水分配系数的新方法研究

建立快速微乳液相色谱法(MELC)测定药物的油-水分配系数(log P)的方法. 选择5种模拟生物膜的微乳流动相体系, 以7个标准药物的log P对保留因子(log k)的回归线性方程, 计算被测药物的log P值. 并以药物文献的log P值对实验测得log k值的线性相关系数为参数, 对微乳体系的表面活性剂和油相的种类进行考察, 得到测定非同类的中性、碱性药物的油-水分配系数最佳流动相体系为6.0% Brij35-6.6%正丁醇-0.8%正辛醇-86.6%磷酸缓冲液(0.05 mol• L－1, pH 7.0), 其测得值与文献的实验值平均相差0.3个对数单位. 结果显示该方法可靠、高效、重现性好, 可用于药物的油-水分配系数log P的测定.     

微乳电动毛细管色谱分离山酮类化合物的影响因素

在优化微乳系统(如pH、缓冲液浓度、表面活性剂、助乳剂、油相及添加剂)的基础上,对影响微乳电动毛细管色谱(MEEKC)分离山酮类化合物的因素进行了系统研究。以正辛醇-水分配系数(疏水常数log P)、色谱峰对称因子和理论塔板数作为参数,研究了分离条件的改变对MEEKC分离性能的影响。结果表明,色谱条件的改变对疏水性山酮和亲水性山酮分离选择性的影响存在着显著差异,当微乳体系为50 mmol/L硼酸缓冲液(pH 9.5)、10%(体积分数)正丁醇、80 mmol/L正庚烷、120 mmol/L十二烷基硫酸钠和     

毛细管微乳电动色谱应用的研究进展

近年来毛细管微乳电动色谱(MEEKC)研究的范围不断扩大,其分离分析的化合物类型也不断增多。该文综述了2002年以来MEEKC应用的研究进展,指出了目前MEEKC研究中存在的一些问题,对今后的研究发展方向进行了展望。     

羧甲基纤维素系列高分子表面活性剂形成微乳液的研究

采用紫外光谱、相图、动态激光光散射、同位素示踪、光学显微镜、电导率等研究了羧甲基纤维素系列高分子表面活性剂与甲苯-水-异丙醇体系微乳液的形成过程,发现微乳液粒子大小均一,形态一致,其尺寸比低分子表面活性剂所形成的微乳液粒子大得多.醇分子插入到油水界面,改变了两相界面结构,促使微乳液的生成.电导率测定表明所形成的微乳液区均为水包油结构,即使在富含甲苯区域,亦不会有油包水的反相胶束形成.     

β-胡萝卜素微乳液的制备及其稳定性研究

通过绘制拟三元相图选择合适的微乳液组分,制备了β-胡萝卜素的Tween80/乙醇/丁酸乙酯/H2O的O/W型微乳液。考察了温度、盐度和pH对微乳液区域的影响:电导率法区分了微乳液的O/W、W/O和B.C(油-水双连续型)区域;对相同浓度β-胡萝卜素的微乳液和丁酸乙酯溶液进行了光、热稳定性研究,用紫外分光光度法测定样品中β-胡萝卜素的残存率。结果表明,温度升高和pH降低使微乳区稍有减小,盐度对微乳区基本无影响;微乳体系中水的质量分数大于61·5%时形成O/W型微乳液;β-胡萝卜素在微乳液和丁酸乙酯溶液中对光和热都比较敏感,但在微乳液中较稳定。     

毛细管微乳液电动色谱的原理及应用

综述了近年来毛细管微乳液电动色谱(MEEKC)的研究进展。对MEEKC的分离原理进行了阐述;对微乳液的组成和其他影响MEEKC分离的因素进行了总结;对MEEKC在各个领域的应用作以分类评述;并将MEEKC和胶束电动毛细管色谱(MEKC)予以比较。     

微乳液结构的研究

测定了十二烷基磺酸钠／正丁醇／２０％苯乙烯／水体系的相平衡，用冷冻刻蚀、ＥＳＲ、ＦＴ－ＩＲ研究了上述体系微乳液的结构，研究表明，苯乙烯含量恒定时，随着体系中水含量增加，电导确定的双连续结构的微乳液经历着从油包水到以连续再到水包油变化，ＦＴ－ＩＲ测定表明，Ｗ／Ｏ微乳兴较Ｏ／Ｗ微乳液的ＯＨ伸缩振动和弯曲振动频率有显著减小，说明Ｗ／Ｏ微乳兴中氢键缔合要比Ｏ／Ｗ强得多。ＥＳＲ测定表明Ｏ／Ｗ微乳液的旋转相关     

微乳液毛细管电动色谱-场放大富集法灵敏分析尿液中的9种麻醉剂类药物

建立了一种微乳液毛细管电动色谱(MEEKC)-场放大富集(FASI)分析尿液中多种麻醉剂(吗啡、可待因、纳洛酮、海洛因、蒂巴因、可卡因、哌替啶、芬太尼、美沙酮)的方法。考察了微乳液组成、分离电压等因素的影响,得到的最佳微乳液组成(质量分数)为0.6%十二烷基硫酸钠、1.2%正丁醇、0.6%乙酸乙酯和97.6% 10 mmol/L硼砂缓冲液(pH 9.5);分离电压为25 kV。在上述微乳体系中,9种化合物在15 min内得到了基线分离。采用场放大在线富集技术提高了分析灵敏度,检出限(S/N=3)低至0.3 μg/L。模拟尿样样品中9种麻醉剂的加标回收率介于79.4%～119.9%之间,日内相对标准偏差小于5.5%。将该方法应用于美沙酮大鼠体外代谢样品的测定,结果令人满意。     

O／W微乳液对Zn（Ⅱ）—PAR的增敏作用

研究了十六烷基三甲基溴化铵９ＣＴＭＡＢ）／正戊醇／正庾烷／水组成的阳离子型Ｏ／Ｗ微乳液对以４－（２－吡啶偶氮）间苯二醇（ＰＡＲ）为显色剂，光度法测定锌的增敏作用。结果，方法简便、快速，与相应的胶束体系为介质比较，提高了测定灵敏度，结果可靠。通过对显色剂在水－微乳液和在水－胶束相中分配系数的测定，初步了微乳液的增敏作用机理。     

具有油水分配系数测算功能的中药指纹图谱

建立了一种能同时测算中药中主要成分的油水分配系数Pow的功能化中药指纹图谱。采用微乳液电动色谱,以中药女贞子为例,对运行缓冲液浓度、pH值、十二烷基硫酸钠浓度等参数进行了优化。利用SPSS程序对磺胺等从女贞子中提取的6种标准化合物组分的迁移时间tm与其log Pow文献值进行非线性拟合,得到女贞子提取组分的标准方程线性关系良好（r=0.9880）。在相同的实验条件下测得化合物的log Pow与文献报道值较好的符合,证明该方法可靠。获得了能代表组分疏水化学特征的中药指纹图谱,测得女贞子的主要有效成分齐墩果酸的log Pow为3.63。该指纹图谱较为可靠地提供了女贞子中各种成分的log Pow,直观地反映出各组分油水分配性质的分布,对中药有效成分提取溶剂的选择、剂型的设计及制剂工艺的改进具有指导意义。     

Improvement of microemulsion electrokinetic chromatography for measuring octanol-water partition coefficients

Microemulsion electrokinetic chromatography (MEEKC) has been used to indirectly measure octanol-water partition coefficients (log P(ow)) of compounds. In order to obtain an accurate log P(ow) value, the electrophoretic mobilities of the microemulsion phase (mu(me)) and the analyte (mu(eff)) in MEEKC must be accurately required. However, in conventional MEEKC, the shortage of obtaining mu(me) with a tracing method was discovered, and the influences of concentration, injection volume of analyte, and high electric field on measuring mu(eff) were also found. In this paper, a novel method called improved MEEKC (I-MEEKC) was developed to avoid the problems mentioned above. In I-MEEKC, a nonlinearity fitting program was used to obtain mu(me) to avoid the error from tracing mu(me); the extrapolating method was used to eliminate the effects of concentrations and injection volumes of analytes on mu(eff) measurement, and an enough stable microemulsion was selected to eliminate the effect of high electric field on mu(eff )measurement. Then the novel method was applied to estimate log P(ow) of uncharged compounds and charged pharmaceuticals compared to the conventional MEEKC. The log P(ow) of all analytes obtained by I-MEEKC agreed with those obtained by classical shake flask or literature values, the errors between them were within 0.1 logarithm units, better than the ones by conventional MEEKC.     

Recent applications of microemulsion electrokinetic chromatography

Compared to MEKC, the presence of a water-immiscible oil phase in the microemulsion droplets of microemulsion EKC (MEEKC) gives rise to some special properties, such as enhanced solubilization capacity and enlarged migration window, which could allow for the improved separation of various hydrophobic and hydrophilic compounds, with reduced sample pretreatment steps, unique selectivities and/or higher efficiencies. Typically, stable and optically clear oil-in-water microemulsions containing a surfactant (SDS), oil (octane or heptane), and cosurfactant (1-butanol) in phosphate buffer are employed as separation media in conventional MEEKC. However, in recent years, the applicability of reverse MEEKC (water-in-oil microemulsions) has also been demonstrated, such as for the enhanced separation of highly hydrophobic substances. Also, during the past few years, the development and application of MEEKC for the separation of chiral molecules has been expanded, based on the use of enantioselective microemulsions that contained a chiral surfactant or chiral alcohol. On the other hand, the application of MEEKC for the characterization of the lipophilicity of chemical substances remains an active and important area of research, such as the use of multiplex MEEKC for the high-throughput determination of partition coefficients (log P values) of pharmaceutical compounds. In this review, recent applications of MEEKC (covering the period from 2003 to 2005) are reported. Emphases are placed on the discussion of MEEKC in the separation of chiral molecules and highly hydrophobic substances, as well as in the determination of partition coefficients, followed by a survey of recent applications of MEEKC in the analysis of pharmaceuticals, cosmetics and health-care products, biological and environmental compounds, plant materials, and foods.     

磷脂微乳电动色谱的定量结构保留关系研究

以大豆磷脂为主要的表面活性剂,制备适合毛细管电动色谱使用的不同构成比的微乳体系, 应用溶剂化参数模型研究了中性溶质在其中的定量结构保留关系.使用动态涂层毛细管, 以二甲基亚砜和十二烷基苯分别作为电渗流和微乳液滴迁移的标记物, 测定了26个具有不同结构小分子中性化合物在17种微乳电动色谱体系下的保留因子, 建立了线性溶剂化能量关系(LSER)方程.通过比较两体系的LSER方程系数比较体系相似性.结果表明, 本研究建立的磷脂微乳电动色谱体系在线性溶剂化特征上和其它构成的微乳电动色谱体系相似.对溶质保留贡献较大的是溶质体积和有效氢键碱度, 油相种类及浓度对溶质的保留选择性无明显影响.     

Screening of octanol-water partition coefficients for pharmaceuticals by pressure-assisted microemulsion electrokinetic chromatography

A rapid screening assay for the determination of octanol-water partition coefficients (log P(OW)) of pharmaceuticals was developed by using pressure-assisted microemulsion electrokinetic chromatography (MEEKC). The microemulsion system contains 50 mM sodium dodecyl sulfate, 0.87 M l-butanol, 82 mM heptane, and 50 mM borate-phosphate (2:3) at pH 10. Ten standard compounds with known log P(OW) values from -0.26 to 4.88 were used for constructing the calibration curve of log P(OW) against the MEEKC retention factor, log k. The log P(OW) values of the compounds were calculated based on the log k values measured by MEEKC and the slope and intercept of the calibration curve. For 13 literature and 32 Roche compounds, about 90% of the log P(OW) values measured by MEEKC are within 0.5 log units of the values from the literature and potentiometric titration. The throughput is about 2 samples/h using +20 kV voltage plus 5 mbar air pressure for separation. This MEEKC method is applicable for log P(OW) screening of weakly basic, weakly acidic, and neutral pharmaceuticals with log P(OW) = 0-5 and pKa < or = 10.     

苯系物Lewis酸碱性的定量化尝试及估算

Lewis酸碱理论研究目前尚处于定性阶段,在环境化学上应用甚少,Gutmann等曾采用热力学与~(31)P NMR方法定量了少量有机溶剂的酸碱性,Kamlet等也利用~(19)F NMR测定了一些有机物的碱性.本文提出了一种利用多种溶剂/水分配系数来定量苯系物酸碱性的方法,该法简便、快速,有广泛的适用性。     

The microemulsion electrokinetic capillary chromatography combined with reversed‐electrode polarity stacking mode for enriching and quantifying lignanoids and ginsenosides in TCMs preparation Shengmai injection

An on‐line large volume sample stacking with polarity switching (LVSS) method was proposed for simultaneously determining lignanoids and ginsenosides in MEEKC. The parameters including the pH value and concentration of buffer solution, SDS, organic modifier, oil phase, running voltage, and temperature as well as injection time, sample matrix, stacking voltage, and time influencing separation and stacking were systematically optimized. The method was verified by performing precision, accuracy, stability, and recovery. Its reliability was proved by separating and quantifying two lignanoids and three ginsenosides in Shengmai injectionSMI. The sensitivity of these compounds was improved by MEEKC‐LVSS method for 6–11 times than conventional MEEKC. Thus, this developed on‐line MEEKC‐LVSS method was sensitive, practical, and reliable.     

Microemulsion electrokinetic chromatography as a suitable tool for lipophilicity determination of acidic,neutral, and basic compounds

In the present work, several MEEKC systems are studied to assess their suitability for lipophilicity determination of acidic, neutral, and basic compounds. Thus, several microemulsion compositions over a wide range of pH values (from 2.0 to 12.0), containing heptane, 1?butanol and different types and amounts of surfactant (SDS or sodium cholate: from 1.3 to 3.3%) are characterized using Abraham's solvation model. The addition of acetonitrile (up to 10%) is also studied, since it increases the resolution of the technique for the most lipophilic compounds. The system coefficients obtained are very similar to those of the 1?octanol/water, used as the reference lipophilicity index, allowing simple and linear correlations between the 1?octanol/water partition values (log P_o/w) and MEEKC mass distribution ratios (log k_MEEKC). Variations in the microemulsion composition (aqueous buffer, surfactant, concentration of ACN) did not significantly affect the similarity of the MEEKC systems to log P_o/w partition.     

Separation and determination of biphenyl nitrile compounds by microemulsion electrokinetic chromatography with mixed surfactants

A mixture of six biphenyl nitrile compounds and three related substances with high hydrophobicity and similar structures was successfully separated by microemulsion electrokinetic chromatography (MEEKC) within 30 min. The microemulsion system contained 100 mM sodium dodecyl sulfate (SDS), 80 mM sodium cholate (SC), 0.81% v/v heptane, 7.5% v/v n-butanol, 10% v/v acetonitrile, and 10 mM borate. The addition of SC, organic modifiers, sample preparation, and temperature all showed remarkable effects on the separation. The capacity factor (k) was calculated by using dodecyl benzene as the marker for microemulsion, and the calculated partition coefficient log P(o/w) of the solutes was in the range of 3.35-7.38. The log k values matched well with the log P(o/w) with a correlation coefficient of 0.96. In addition, the linear correlation coefficients of each compound between peak area and concentration were from 0.996 to 0.998 with the repeatability RSD value < 1.2% for migration time and < 4.8% for peak area, and the highest theoretic plate number was > 586000. MEEKC was compared with micellar electrokinetic chromatography (MEKC) indicating that the former method is more suitable for this separation and can be used for the quality control of biphenyl nitrile compounds in the synthesis of liquid crystals.     

Application of microemulsion electrokinetic chromatography to the analysis of a wide range of pharmaceuticals and excipients

Microemulsion electrokinetic chromatography (MEEKC) is a capillary electrophoresis (CE) technique in which solutes partition with moving oil droplets present in a microemulsion buffer. Ionised species will also separate by electrophoresis. In this paper MEEKC is shown to give highly efficient and relatively rapid separations for a wide range of pharmaceuticals, vitamins and excipients. A single set of operating conditions was used to resolve both water-soluble and insoluble compounds. The method was also used to separate both ionic and neutral compounds. The method was especially useful in the analysis of water-insoluble neutral compounds such as steroids and lecithin, which are difficult to analyse by CE. The method was found to be both quantitative and highly repeatable. The quality of the separation was found to be dependent upon the sample diluent used if large injection volumes are employed. The use of MEEKC for the determination of complex mixtures such as multi-ingredient formulations and drug-related impurities was successfully demonstrated. MEEKC offers significant advantages over many forms of CE and capillary electrochromatography (CEC) and should be considered as an extremely useful option in pharmaceutical analysis.