Reversed Phase High Performance Liquid Chromatography with Cetrimide Containing Eluents

Abstract

A radially compressed column, packed with micro particle, reversed phase (C 18) material, was used to study HPLC with cetrimide containing eluents. The amount of cetrimide adsorbed onto the stationary phase was measured; not the number of available adsorption sites, but rather the presence of micelles in the eluent appears to be the limiting factor for the uptake of cetrimide from the eluent.

The capacity factors, κ′, of several - mainly acidic - compounds were determined in this system, with varying pH and cetrimide concentration of the eluent (methanol-water, 50% w/w). The results obtained upon changing the pH of the eluent can not all be explained with an ion-exchange (or ion-pair) model.

Upon increasing the cetrimide concentration, maximum values in κ′ are reached at about the critical micelle concentration (cmc) of cetrimide in the eluent. The results of conductimetric experiments suggested, that the decrease of κ′ at cetrimide concentrations above this CMC, observed for most of the compounds, can be explained by partitioning of the solutes between the micelles and the bulk of the mobile phase. From these experiments it was also clear that ion-pair formation between cetrimide and solutes is possible.     

反相色谱多二元溶剂的选择性调整

从统计热力学方法推导的溶质保留规律及其相关参数与分子结构之间的关系式出发,探讨了１６种多环芳烃在甲醇／水、乙腈／水、异丙醇／乙腈３种二元溶剂体系下选择性的差异,为确立复杂化合物分离的溶剂选择原则奠定了基础。     

Surface Heterogeneity Effects in Liquid-Solid Chromatography with Mixed Eluents

Abstract

Equations describing liquid-solid chronatography (LSC) systems with ideal surface and bulk phases and heterogeneous adsorbents are derived and discussed. It is shown that for a nixed surface phase formed on a heterogeneous solid surface the dependence of In k_s on In x^l ₁ is linear for higher concentrations of the first solvent and its slope is a function of the ratio of molecular sizes of solute and solvents, heterogeneity parameters and equilibrium constants describing phase exchange between solute and solvent molecules. However, for complete coverage of the surface by molecules of the first solvent this linear dependence becomes the Snyder-Soczewiński relationship, in which the slope depends solely on the ratio of molecular sizes of the solute and solvents. These results and an analysis presented herein also demonstrate that a recently proposed interpretation of the Snyder-Soczewiński equation in incorrect.     

Reversed-Phase Liquid Chromatography with Mixed Eluents: Partition Model of Retention for Ionogenic Solutes

Abstract

Basing on the pure partition model of solute retention new theoretical equations for ionogenic solutes are discussed. These equations define dependence of the capacity ratio on the mobile phase composition, which is characteristic for the reversed-phase liquid chromatography.     

反相液相色谱中柱相比的影响因素

从理论上阐明了热力学观点所定义的柱相比（即溶质的保留自由能变为零时的κ′值）与溶质种类、柱温、固定相以及溶剂种类的依赖关系。通过研究3种配基链长不同的固定相对7种非极性苯的取代物溶质保留行为的影响，发现柱相比与固定相对溶质吸附力有关；通过对9种正链烷溶质在4种温度下的保留行为的研究，发现了柱相比随温度升高而增大，也发现了柱相比与同系物溶质的碳数无关；通过对3种正链醇同系物，3种正链酸同系物，以及丙酮、乙腈和异丙醇共9种置换剂对9种烷基醇同系物溶质色谱保留行为影响的研究，发现柱相比随溶剂极性增大而减小。     

An Integrated Theory of Adsorption and Partition Mechanism and Eash Contribution to Solute Retention in Reversed Phase Liquid Chromatography

With the combination of the the stoichiometric displacement model for retention (SDM-R) in reversed phase liquid chromatography (RPLC) and the stoichiometric displacement model for adsorption (SDM-A) in physical chemistry,the total number of moles of the re-solvated methanol of stationary phase side.nr,and that of solute side in the mobile phase,q,corresponding the one mole of the desorbing solute,were separately determined and referred as the characterization parameters of the contributions of the adsorption mechanism and partition mechanism to the solute retention,respectively.A chromatographic system of insulin,using mobile phase consisting of the pseudo-homologue of alcohols(methanol,ethanol and 2-propanol)-water and trifluoroacetic acid was employed.The maximum number of the methanol layers on the stationary phase surface was found to be 10.6,only 3 of which being valid in usual RPLC,traditionally referred as a volume process in partition mechanism.However,it still follows the SDM-R.Both of q and nr of insulin were found not to be zero,indicating that the retention mechanism of insulin is a mixed mode of partition mechanism and adsorption mechanism.When methanol is used as the organic modifier,the ratio of q/nr was 1.13,indicating the contribution to insulin retention due to partition mechanism being a bit greater than that due to adsorption mechanism.A linear relationship between q,or nr and the carbon number of the pseudo-homologue in the mobile phase was also found.As a methodology for investigating the retention mechanism retention and behavior of biopolymers.a homologue of organic solvents as the organic modifier in mobile phase has also been explored.     

Reversed Phase High Performance Liquid Chromatography Using Carboxylic Acids in the Mobile Phase

Abstract

This report describes the use of different carboxylic acids as mobile phase modifiers. The effect on retention of acid chain length, pH, and eluent composition for a series of phenylalkanols, phenol, and the amines aniline, N-methylaniline, and benzylamine is discussed. The retention of both neutral and positively charged compounds is influenced by the dissociation equilibrium of the carboxylic acid in the mobile phase. By using l-pentanol to coat excess exposed silanol groups on the reversed phase column used, the inflection in the retention of both neutral and charged solutes as pH is changed occurs at the pK_a of the acid in the mobile phase. In addition, by using an acid and amine with the same or similar pK_a values, selective ion-pairing of this pair over others with dissimilar pK_a values can be promoted. Application of this technique to the selective retention of amino acids and peptides was unsuccessful.     

Ethylammonium Acetate as a Mobile Phase Modifier for Reversed Phase Liquid Chromatography

We have synthesized the low melting hygroscopic ionic liquid ethylammonium acetate (EAA) and characterized a concentrated solution of EAA as a reversed phase mobile phase replacement for organic solvents like methanol. This solution of EAA acts like an organic solvent with a polarity parameter (P=6.0) similar to methanol (P=5.1) but less than water (P=10.2). A test mixture of salicylate, nitrofurantoin, and acetophenone was separated in this order on C1, C4, and C18 columns using an EAA modified aqueous mobile phase. On a C-18 column, the reduction in retention factor for acetophenone from about 20 to 2 as the % EAA is raised from 20–80% is similar to the same trend found using methanol. However, the retention order using methanol is first nitrofurantoin, then salicylate, and finally acetophenone. Log retention factor (k) versus the volume fraction of either EAA or methanol plots were linear indicating the solvent strength parameter for EAA was about 85% of that for methanol. Despite the relatively high viscosity of EAA, plate count values averaged only about 15% less for EAA as compared to methanol using the same mobile phase composition and could be raised by either working at a temperature above ambient or reducing the flow rate. EAA as a modifier allowed for faster separations of water-soluble vitamins on a reversed phase column designed for totally 100% aqueous mobile phases.Acknowledgements This work was supported by a grant from the Miami University Committee on Faculty Research. We thank ES Industries for the gift of the AquaSep column.     

Determination of Neomycin in Milk by Reversed Phase Ion-Pairing Liquid Chromatography

Abstract

A fluorometric high performance liquid chromatographic (HPLC) method has been developed for the determination of neomycin in milk. Whole or shelf milk was defatted by initial centrifugation at 4°C. The resulting skim milk was deproteinated with trichloroacetic acid and centrifuged again. The neomycin was determined directly in the supernate by HPLC. The HPLC conditions consisted of an ion-pairing mobile phase, a reversed-phase column, post-column derivatization with o-phthalaldehyde (OPA) reagent and fluorescence detection. The overall recovery of neomycin was 94% (coefficient of variation 6.5%), in whole milk spiked at 0.15–10 ppm and 99% (coefficient of variation 6.4%) in shelf milk spiked at 0.15–5 ppm. The method was used to detect neomycin in milk obtained from cows dosed intramuscularly with neomycin (10 mg/kg). The neomycin concentrations in milk at 8 and 24 h after dosing were 0.3 and 0.2 ug/ml, respectively.     

蛋白质的反相液相色谱保留方程研究

要以胰岛素、细胞色素C、溶菌酶、转铁蛋白和肌红蛋白5种标准蛋白为研究对象,将6种浓度的标准蛋白在反相色谱(Waters Symmetry 300 C4、Waters Symmetry 300 C18、C8 HC)的保留时间非线性拟合(CSASS软件),获得了5种蛋白质在3种色谱柱的lnk=α+cCB方程,15个方程的回归系数均大于0.999,证实方程Ink=a+cCB可准确地描述蛋白质在反相色谱的保留规律.运用该方程可预测蛋白质在其它梯度条件下的保留时间,预测值和实验值的相对误差均小于5％.该方程还可用于蛋白质混合物的梯度分离的优化,20 min内可实现5种标准蛋白的基线分离.     

聚合物涂敷反相高效液相色谱固定相

对聚合物涂敷反相高效液相色谱固定相的制备及其特性进行了综述。根据制备方法对固定相进行了分类,并指出该类固定相对色谱峰拖尾现象的改善引人注目,且就涂敷物对基质孔径及色谱性能的影响进行了讨论。另外,对该类固定相的稳定性进行了阐述。     

反相液相色谱中同系物保留过程中的等焓点

依据液相色谱中溶质计量置换保留模型,从理论上分别推导了出在反相高效订色谱（ＲＰＬＣ）中同系物端基和重复结构单元对Ｚ（１ｍｏｌ溶剂化溶质被固定相吸附时,在其接触表面释放出溶剂的摩尔总数）与绝对温度倒数间的线性关系式。也从分子结构参数推荐导出了同系物端基对总变的贡献△Ｈ,和同系物非端基（或键长）对总焓变的贡献△ＨｓＮｃ的表达式。从而建立了等焓点的坐标方程,阐明了等点的纵坐标相是溶质在等点处的变为零,等     

反相液相色谱对多肽的分离、纯化与制备

用反相高效液相色谱（RPLC）对两种化学合成多肽－－32肽和21肽进行了分离、纯化和制备。在用分析型RPLC色谱柱对多肽样品的制备过程中，对其进样量和洗脱梯度进行了选择。每次进样量为5mg，在最优化色谱条件下，用RPLC一步就可对21肽进行分离纯化，其纯度达到98.6%。而32肽由于样品组分更加复杂，RPLC一步纯化后其纯度仅有80％。通过对色谱分离条件的再次优化，对32肽进行二次分离纯化，纯度达杂，RPLC一步纯化后其纯度仅有80％。通过对色谱分离条件的再次优化，对32肽进行二次分离纯化，纯度达到96.4%。在其最优化条件下，通过多次样品收集和冷冻干燥，分别制备了高纯度的21肽和32肽各100mg。     

On the Determination of the Hold-Up Time in Reversed Phase Liquid Chromatography

Abstract

The determination of the hold-up time in reversed phase liquid chromatography has been studied extensively for the mobile phase system methanol-water. Hold-up times obtained by static methods, linearization of homologous series and so-called “unretained compounds” are discussed and mutually compared. Several n-alkyldimethylsilyl bonded phases have been used for this investigation.

A rough estimate of the hold-up time can be obtained by using components of the mobile phase or highly concentrated salt solutions, but only for mobile phase compositions around 60% (v/v) methanol. Hold-up times accurate to 1% can be obtained over the complete range of mobile phase compositions from the linearization of net retention times of homologous series.     

Isocratic Separation of Some Food Additives by Reversed Phase Liquid Chromatography

In recent years, concern about food safety has been growing. The use of food additives in different countries is limited by specific regulations. Therefore, analytical methods that simultaneously determine artificial sweeteners and preservatives are advantageous. High performance liquid chromatography has been the most popular choice for the determination of food additives. In this study, reversed-phase liquid chromatography was developed for the separation of α-aspartame, sodium saccharin, acesulfame-K, vanillin, sorbic acid and benzoic acid. The effects of the proportion of the organic modifier on the chromatographic separation were investigated in order to separate these additives. The results showed that optimum chromatographic separation for these compounds takes place when the acetonitrile content in the mobile phase was 15% containing ammonium acetate buffer (0.005 M). It was concluded that the best separation was obtained with YMC-ODS pack column by using this mobile phase at pH 4.0. All additives were separated within 40 min. The RP-HPLC-UV method was validated in terms of LOD/LOQ, linearity, recovery and repeatability. This method was used for the determination of α-aspartame, acesulfame-K and benzoic acid in cola and instant powder drinks.     

反相高效液相色谱法分离蛋白质的研究

采用反相高效液相色谱法考察了几种大孔硅胶烷基键合固定相在等度淋洗条件下进行蛋白质分离的色谱性能。研究了冲洗剂中有机溶剂异丙醇的浓度、离子对酸（ＴＦＡ）浓度对蛋白质保留时间的影响。探讨了蛋白质在ＲＰ－ＨＰＬＣ中的保留机理。结果表明,大孔硅胶（２０～３０ｎｍ）短链（Ｃ４和Ｃ８）烷基键合固定相适合蛋白质的分离。     

Determination of Ticarcillin in Serum by Reversed Phase High Performance Liquid Chromatography

Abstract

Ticarcillin is a semi-synthetic penicillin useful against several Pseudomonas species. In order to easily quantitate this drug, a new procedure was developed whereby ticarcillin in serum is converted to its free acid form by the addition of citric acid and, subsequently, extracted into ethyl acetate. The organic extract which contains the nonionized form of ticarcillin is dried under nitrogen, the sample is reconstituted with mobile phase and analyzed by high performance liquid chromatography. Elution is completed in less than five minutes. The assay is linear from 1 mg/L through 100 mg/L. The correlation coefficient of ticarcillin concentration to peak area (r) was 0. 999 over this concentration range. The small sample volume (100 yl) makes this assay particularly suitable for pediatric patients.     

葡萄酒中游离氨基酸的高效液相色谱法测定

采用邻苯二甲醛衍生化法衍生葡萄酒中的游离氨基酸，以反相高效液相色谱法对葡萄酒中１８种氨基酸进行了测定，方法简单、迅速，２５ｍｉｎ即可完成１８种氨基酸的分离。精密度及回收率实验结果令人满意。     

固相萃取反相高效液相色谱法测定人血清中洛美利嗪浓度

实验建立了固相萃取反相高效液相色谱法测定血清中洛美利嗪的浓度。采用W aters Oasis HLB萃取小柱对血清样品进行固相萃取,以氟桂利嗪为内标,在W aters高效液相色谱系统上,C8为固定相,乙腈-水(67∶33,含0.2%三乙胺,磷酸调节pH至6.5)为流动相,流速:1 mL/m in;检测波长:223 nm;柱温:30℃;实验结果显示洛美利嗪和内标物洗脱时间分别为9.9 m in和10.8 m in,与血中内源性杂质得到良好分离。方法的相对回收率为99.6%~106.1%;绝对回收率为61.8%~86.5%;日内日间变异RSD范围分别为3.6%~5.3%和2.7%~6.9%;线性范围为5~320μg/L(n=7,r=0.9998)。当S/N=3时,洛美利嗪最低检出浓度可达5μg/L。所建方法准确、灵敏,可满足血药浓度监测和药代动力学参数测试的需求。