Selective separation and purification of highly polar basic compounds using a silica-based strong cation exchange stationary phase

Compared to moderately and weakly hydrophilic bases, highly polar basic compounds are even more difficult to separate due to their poor retention in reversed phase (RP) mode. This study described the successful applications of a strong cation exchange (SCX) stationary phase to achieve symmetric peak shape, adequate retention and selectivity in the separation of very polar basic compounds. Salt and acetonitrile concentrations were adjusted to optimize the separation. Good correlations (R² = 0.998–1.000) between the logarithm of the retention factor and the logarithm of salt or acetonitrile concentration were obtained. Gradients generated by changing salt or acetonitrile concentration were compared for the analysis of different highly polar bases. Although all of the analytes were eluted more quickly with an acetonitrile gradient, the effect of the gradients tested on peak width and peak shape varied with respect to analyte. In addition, the effects of different types of cation and anion additives were also investigated. After separation parameters were acquired, the SCX-based method was utilized to analyze highly hydrophilic alkaloids from Scopolia tangutica Maxim with high separation efficiency (plate numbers > 32,000 m⁻¹). Concurrently, one very polar alkaloid fraction was purified with symmetric peak shape using the current method. Our results suggest that SCX stationary phase can be used as an alternative to RP stationary phase in the analysis and purification of highly hydrophilic basic compounds.     

强阳离子交换色谱分离多肽混合物的条件优化

以酵母全蛋白提取液的胰蛋白酶切产物为研究对象,对多维色谱分离中常用的强阳离子交换色谱的分离条件,包括上样量、盐的种类、调节缓冲液pH值的酸的种类及有机溶剂的比例进行了考察和比较。结果表明,在强阳离子交换色谱分离线性上样量范围内,在氯化铵溶液作为流动相,用磷酸调节流动相缓冲液pH值至2.7,且流动相中乙腈的体积分数为30%条件下进行梯度洗脱时,可获得最佳的分离结果。本结果可为采用二维色谱-质谱策略分析多肽混合物时的第一维强阳离子交换色谱分离条件的选择提供有益的参考。     

Effect of ion exchange by an organic cation on platinum immobilization on clays

Clay-supported platinum catalysts were prepared by ion exchange. The platinum precursor has been reduced either in the presence or in the absence of cinchonidinium cations introduced in the interlamellar space of the cationic clay. The samples were characterized by XRD and TEM. Reduction by NaBH₄ in the absence of cinchonidinium cations and the subsequent introduction of this latter ensured the formation of monodispersed, small platinum crystallites immobilized mostly between the clay sheets. On the other hand, reduction in the presence of the organic cations resulted in migration of the platinum particles on the external surface of the clay.     

强酸性阳离子交换树脂催化合成醋酸正丁酯的动力学研究

以强酸性阳离子交换树脂Amberlyst 15作为催化剂,研究了醋酸与正丁醇合成醋酸正丁酯的反应动力学;考察了搅拌速度、催化剂粒径、温度、催化剂用量,以及酸醇物质的量之比对醋酸转化率的影响;建立了拟均相动力学模型,对实验数据进行了拟合,并估算了相应的动力学参数.结果表明,由拟均相动力学模型得到的计算值与实验值吻合较好.     

The influence of exchangeable cation on thermal behaviour of ground vermiculite

Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect (escaping up to 150°C) and increased the second dehydration effect (150 to 500°C). The dehydroxylation was moved to lower temperatures and was only ΔM(500-1100°C)=3.7±0.3 % as compared to 5.5% in the parent vermiculite (V). Except ΔM(20-150°C), the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused the homogenization of the crystal structure of vermiculite [ΔM(150-500°C)=7.6±0.7%]. DTA curves after grinding and cation exchange indicate an important exothermal peak at 795-870°C, its temperature depending on exchangeable cation. It indicates the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795°C) was observed in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870°C) was found in V-gr-K, where almost only forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparative effect of cyclodextrin nanocavities versus organic solvents on the fluorescence of carbamate and indole compounds

The effect of the addition of different amounts of organic solvents (S) on the fluorescence of aromatic compounds (C) and their inclusion complexes with β-cyclodextrin (βCD) and hydroxypropyl-β-cyclodextrin (HPCD) has been examined using steady-state measurements. Carbamate pesticides with different aromatic moiety, such as carbofuran (CF), promecarb (PC), carbaryl (CY) and bendiocarb (BC) were used, as well as indole derivatives with different polarity in their lateral chains, such as melatonin (M, neutral), 5-methoxytryptamine (MT, cation) and auxin (IA, anion). Their complexes in water show a fluorescence signal higher than that obtained for the free substrates in solvent:water mixtures (30%, v/v n-propanol or acetonitrile, and 50%, v/v methanol). The isofluorescent point (IF), the %IF and the F_85% are defined in order to evaluate the use of CD nanocavities as a non-polluting alternative for the analysis of the compounds analyzed.Apparent formation constants (K_AP, M⁻¹) for the complexes of C:HPCD at different solvent percentages were determined for CF and PC with methanol (MeOH), n-propanol (ProOH) and acetonitrile (ACN), and for indole compounds with ACN. A decrease in the K_AP values for the CF:HPCD (120–30) and PC:HPCD (2000–400) complexes occurs in accordance with the solvent affinities for CDs (MeOH < ACN < ProOH). Nevertheless, in the indolic series, the polar characteristics of MT, IA and M determine their behaviour in the presence of ACN. For the neutral substrate M, K_AP decreases with the increasing percentage of ACN (100–10). In contrast, for IA and MT (ionic substrates) K_AP increases (10–100).These results may be accounted for by two different mechanisms: the competition between C and S for the cavity of the receptor or the formation of ternary complexes C:S:CD with additional stabilization.     

Hydrophobic and cation exchange mechanisms in the retention of basic compounds in a polymeric column

A cation exchange retention mechanism concomitant with the well-known hydrophobic partition mechanism in a polymeric column has been observed and investigated. This exchange process is attributed to ionization of some acidic sites present in the polymer column at basic mobile phase pH values. Several drugs of different basicity have been chromatographed on a polymeric PLRP-S column with methanol-water and acetonitrile-water mobile phases. The cation exchange between the protonated basic drug and the buffer cations (Na+, K+ and BuNH4+) is observed at the pH range where the protonated drug and the ionized sites of the column coexist. This process produces a shift of the retention versus pH plot of the base to pH values lower than those expected from the pKa of the base as well as a maximum in the plot at basic pH values. These effects are more pronounced for acetonitrile-water mobile phases.     

The use of ligand exchange for the separation of aromatic acids on synthetic cation exchangers

Summary A very good separation of the mixture of eight aromatic acids has been obtained by ion-exchange chromatography using the ligand-exchange technique, on a column containing a synthetic cation exchanger and trivalent metal ion (Al³⁺, Fe³⁺, or Ce³⁺).     

无孔单分散亲水性中强阳离子交换树脂的制备及其在蛋白质快速分离中的应用研究

以3.0μm无孔单分散亲水性交联聚甲基丙烯酸环氧丙酯树脂为基质,将其表面经新的化学方法改性后制备了一种新型的无孔中强阳离子交换色谱填料。详细考察了该无孔填料对标准蛋白分离性能,有机溶剂、pH、流动相盐种类和流速等对蛋白质保留的影响。实验结果表明,在流速为4 mL/min时,线性梯度时间在2.0 min内可快速分离4种标准蛋白,蛋白质的保留符合阳离子交换色谱规律。将其应用于快速纯化鸡蛋清中的溶菌酶,取得较好效果。     

Preparation of magnetic strong cation exchange resin for the extraction of melamine from egg samples followed by liquid chromatography-tandem mass spectrometry

In the work, magnetic strong cation exchange (MSCX) resins were prepared using hydrophobic Fe₃O₄ magnetite as the magnetically susceptible component, styrene and divinylbenzene as polymeric matrix components, acetyl sulfonate as the sulfonation agent. The resins were successfully applied to the extraction of melamine (MEL) from egg samples. The extraction procedure was carried out in a single step by blending and stirring the sample, extraction solvent and the magnetic resins. The MEL was extracted from the sample matrix then adsorbed onto the resins directly through ion-exchange interaction. When the extraction was completed, the resins with adsorbed analyte were easily separated from the sample matrix by applying an appropriate magnetic field. Main factors affecting the extraction of MEL such as the amount of MSCX resins, extraction time, washing and eluting conditions were optimized. The MEL eluted from the resins was determined by liquid chromatography-tandem mass spectrometry. The linearity of quantification obtained by analyzing matrix-matched standards is in the range of 10-1000 ng g⁻¹. The limit of detection and quantification obtained are 2.6 and 8.8 ng g⁻¹, respectively. The relative standard deviations of intra- and inter-day ranging from 1.6% to 6.5% and from 2.1% to 7.2% are obtained. The recoveries of MEL are in the range of 77.2-99.3%. The proposed method was successfully applied to determine MEL in eggs obtained from different local markets. MEL was detectable with the contents of 43.5 and 234.1 ng g⁻¹ in two samples.     

强阳离子交换毛细管液相色谱-反相加压毛细管电色谱二维系统的构建及其在中药黄柏提取物分离中的应用

加压毛细管电色谱(pCEC)具有电泳和液相色谱的双重分离机理,其柱效高、选择性强、分辨率高和分离速度快并可进行梯度洗脱。我们在此基础上加入离子交换色谱模式,构建了强阳离子交换-反相加压毛细管液相色谱(micro strong cation exchange liquid chromatography/reversed phase pressurized capillary electrochromatography, μ-SCXLC/RP-pCEC)二维系统,并对中药黄柏的提取物进行了优化分离。第一维μ-SCXLC采用线性盐梯度分离,样品被切割成11个馏分洗脱收集后进入第二维,第二维脱盐后,采用RP-pCEC进行分离分析,梯度洗脱。以中药黄柏提取物为样品,此二维系统的分辨率和峰容量都较一维系统有很大提高,理论峰容量可达900左右,证明构建的二维体系非常适合复杂样品的分离分析。     

Microcalorimetric study of the adsorption of PEGylated lysozyme on a strong cation exchange resin

Adsorption of native as well as mono-, di-, and tri-PEGylated lysozyme on Toyopearl Gigacap S-650M in sodium phosphate buffer is studied by isothermal titration calorimetry and by independent adsorption equilibrium measurements at pH 6 and 25°C. The production and separation of PEGylated lysozyme is discussed. Two different PEG sizes are used (5 kDa and 10 kDa) which leads to six different forms of PEGylated lysozyme which were systematically studied. The sodium chloride concentration is varied according to the elution conditions in the production process. The specific enthalpy of adsorption Δh(p)(ads) is determined from the calorimetric and the adsorption equilibrium data. It was found to be exothermal and constant with increasing adsorber loading for native lysozyme. For all PEGylated forms there is an influence of the adsorber loading on Δh(p)(ads) which is found to become more important with increasing PEGylation degree (total molecular weight of conjugated PEG). At low loadings the adsorption of all PEGylated lysozyme forms is exothermal. With increasing loading the adsorption becomes less exothermal and for the species with higher PEGylation degree also endothermal effects are observed at higher loadings. A thermodynamic analysis is carried out by which the enthalpic and entropic contributions to the binding constants are quantified. The findings are discussed on a molecular level. The results provide insight into the adsorption mechanisms of polymer-modified proteins on chromatographic resins.     

The selection of optimal conditions in HPLC II. The influence of column dimensions and sample size on solute detection

Summary The responding signals of eluted components can be enhanced by using high performance small volume columns with long lengths generating more plates than required for a separation with a preset resolution in combination with instruments which show very small external bandbroadening. The excess number of plates is then consequently erased by maximizing the injection volume of the sample until the preset resolution is reached. Equations, describing the dilution, relative signal enhancement and maximum injection volume as a function of the process parameters are derived and experimentally verified. Theory and experiment are in agreement only if variances of response functions are calculated as their second normalized central moments.     

Comments on the separation efficiency of asymmetrical flow field-flow fractionation in channels of constant channel and crossflow velocities leading to constant separation efficiency

It is shown theoretically that a claim in the literature about the overall separation efficiency of asymmetrical flow FFF channels being improved by geometries that permit a uniform channel flow velocity throughout the channel length is untrue.     

Study on the influence of humic acid of different molecular weight on basic ion exchange resin's adsorption capacity

In this paper, humic acid (HA) was ultra-filtered into different molecular weight sections and was characterized by multi-element analysis, UV₂₅₄/TOC, FT-IR and three-dimensional fluorescence spectrometric. Since humic acids of different molecular weights have different hydrophilic and molecular size, the maximum adsorption capacity of basic ion exchange resins appears on the humic acid whose molecular weight ranges from 6000 to 10,000 Da.     

基于微阵列聚焦电泳的糖尿病血样临床阳离子交换高效液相色谱图中血红蛋白A3峰位置推测

血红蛋白A1c(HbA1c)是糖尿病诊断的关键生物标志物,目前其常用的分析方法为阳离子交换高效液相色谱法(CX-HPLC,5/50 mm分离柱),此方法虽然具有稳定、快捷与自动化等众多优点,但临床CX-HPLC(VARIANTⅡsystem)谱图中仍存在未知峰,尤其干扰HbA1c准确测定的谷胱甘肽化血红蛋白A3(HbA...     

The chromatographic behavior of arsenic compounds on anion exchange columns with binary organic acids as mobile phases

Summary Identification and quantification of arsenic compunds was performed with high- performance liquid chromatography (HPLC) and flame atomic absorption spectrometry (FAAS) as element-specific detector. Arsenous acid, methylarsonic acid, dimethylarsinic acid, arsenic acid, arsenobetaine, and arsenocholine were separated on two anion-exchange columns (Synchropak Q 300 and PRP-X 100) with different binary organic acids as mobile phases. The infleunce of chromatographic parameters, such as pH and the concentration of the mobile phase were investigated. An unusual chromatographic behavior of arsenous acid was observed when tartaric acid was used as mobile phase.     

The effect of the exchangeable metallic cation on the colloid properties of laponite treated with acridine orangea spectrophotometric study

The adsorption of the cationic dye acridine orange (AO) by different monoionic laponites leads to changes in the colloid properties of this synthetic mineral in aqueous solutions. The organic cation is adsorbed by the mechanism of cation exchange. Small amounts of adsorbed dye keep the clay in a peptized state with all metallic cations. Greater amounts of AO result in the neutralization of the electric charge of the clay, and its flocculation. In excess AO the charge of the clay platelets becomes positive and the clay is peptized. The colloid properties are studied by absorbance curves in which the absorbance is described as a function of the degree of saturation with constant clay concentrations or with constant dye concentrations. In the absorbance curves three regions can be identified. The transition between the first and second or the second and third regions depend on the exchangeable metallic cation initially present in the clay. The spectrophotometric method is useful in identifying the presence of tactoids and flocculation mechanism, whether it results in card-house or in book-house flocs.     

The effect of aqueous organic solvents on the dissociation constants and thermodynamic properties of alkanolamines

The dissociation constants of protonated monoethanolamine and N-methyldiethanolamine have been determined in methanol–water, ethanol–water, and t-butanol–water solvents. The alcohol mole fractions were ranging from 0.2 to 0.95 and the temperatures from 283 to 323 K, 283 to 333 K, and at 298.15 K, respective to the different solvents. The experimental results are reported with the standard state thermodynamic properties. The basic strength of the protonated alkanolamine decreases with decreasing dielectric constant and increasing temperature of the solvent.