Cellulose acetate as stationary phase in microcolumn LC

The retention characteristics of alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) have been examined in liquid chromatography on a microcapillary column packed with cellulose acetate. Particulate and fibrous cellulose acetate were used as the stationary phase. Fibrous cellulose diacetate was found to be of use as an alternative stationary phase for liquid chromatography, although the separation efficiency was low. The retention characteristics for planar PAHs were linearly correlated with the size of the molecules, but the retention behavior for alkylbenzenes and nonplanar PAHs was affected by exclusion. The retention order was strongly influenced by the addition of dimethylformamide or water to methanol in the mobile phase. The results suggested that the retention behavior is influenced by a slight change in the polymer matrix of cellulose acetate.     

Polyhedral oligomeric silsesquioxanes as functional monomer to prepare hybrid monolithic columns for capillary electrochromatography and capillary liquid chromatography

A simple approach to fabricate hybrid monolithic column within the confines of fused-silica capillaries (75 μm i.d.) was introduced. A polyhedral oligomeric silsesquioxanes (POSS) reagent containing a methacrylate group was selected as functional monomer, and copolymerized with bisphenol A dimethacrylate (BPADMA) or ethylene dimethacrylate (EDMA) in the presence of porogenic solvents via thermally initiated free radical polymerization. After optimization of the preparation conditions, two POSS-containing hybrid monoliths were successfully prepared and exhibited good permeability and stability. By comparison of the separation efficiencies of the resulting poly(POSS-co-BPADMA) and poly(POSS-co-EDMA) monoliths in capillary electrochromatography (CEC) and capillary liquid chromatography (cLC), it was indicated the former has better column efficiencies for alkylbenzenes, phenols, anilines and PAHs in CEC and cLC than the latter. Particularly, the hybrid poly(POSS-co-BPADMA) monolith is more suitable for separation of PAHs due to π–π interaction between the analytes and aromatic rings in the surface of monolithic stationary phase.     

腰果酚键合硅胶固定相的制备及其色谱性能北大核心CSCD

天然产物作为一种绿色低毒、来源广泛、功能位点丰富的单体,已被广泛应用于色谱固定相的研制与开发。该文以天然可再生资源腰果酚为配体,通过一步法开环反应将其接枝到由γ-缩水甘油醚氧丙基三甲氧基硅烷(KH-560)修饰的硅胶上,制备得到腰果酚键合硅胶固定相。利用傅里叶红外光谱、元素分析、热失重分析和N_(2)吸附脱附实验对固定相进行表征,结果表明成功制备了腰果酚键合硅胶色谱固定相。采用Tanaka实验试剂、烷基苯、多环芳香烃、苯酚类化合物和芳香族位置异构体为探针评价其分离性能和保留机制,并与C_(18)柱进行对比。研究发现,腰果酚键合固定相除疏水作用外,还具有π-π和氢键作用。基于上述保留作用,腰果酚键合硅胶固定相对测试探针表现出良好的分离性能。重复进样10次,各探针保留时间的RSD为0.052%~0.079%,峰面积的RSD为0.104%~0.847%,峰高的RSD为0.081%~0.272%,表明该色谱柱具有良好的重复性和稳定性。此外,腰果酚键合硅胶色谱柱对中药喜树果和吴茱萸果的粗提物具有良好的分离性能,验证了其在实际样品分析中的巨大潜力。将天然产物腰果酚用于色谱固定相的制备,为分离纯化喜树碱和吴茱萸提供了新的方法,同时拓展了腰果酚在色谱分离材料方面的应用。     

N-methylimidazolium-functionalized monolithic silica column for mixed-mode chromatography

The development of mixed-mode stationary phase to achieve multiple separation capabilities in one column is very important for high performance liquid chromatography. In this paper, a new specific stationary phase based on grafting N-methylimidazolium to a monolithic silica column was successfully prepared for performing capillary liquid chromatography. The characteristics of the column were evaluated by the separation of different types of compounds including inorganic anions, aromatic acids, nucleotides, polycyclic aromatic hydrocarbons, alkylbenzenes, and phenols. The mechanisms for the separation of these compounds were investigated and appeared to involve the mixed interactions including anion-exchange, hydrophilic, π-π, dipole-dipole, and hydrophobic interactions.     

溴化1-乙烯基-3-十二烷基咪唑硅胶键合固定相制备及其色谱性能

膜脂作为细胞质膜的主要组成部分,在生命活动中扮演着重要的作用,其涉及多种重要疾病的发生和发展过程。发展适用于膜脂分离分析的新型色谱材料对于其后续结构和生物学功能研究具有重要的意义。该文选用具有潜在生物相容性的离子液体溴化1-乙烯基-3-十二烷基咪唑（1-vinyl-3-dodecylimidazole bromide,VDI）为功能单体,通过一步法点击反应将其接枝到巯基功能化硅球表面,制备得到了新型溴化1-乙烯基-3-十二烷基咪唑硅胶键合固定相（Sil-VDI）。利用傅里叶变换红外光谱仪和热重分析仪对Sil-VDI固定相材料的结构进行表征,结果证明Sil-VDI色谱固定相已被成功制备。保留机制研究显示填充Sil-VDI色谱柱具有典型的反相/离子交换混合模式保留特性。基于此,采用不同疏水性物质烷基苯、多环芳烃、苯胺、苯衍生物和无机阴离子BrO₃ ^- 、NO₃ ^- 和IO₃ ^- 为测试物,对所制备固定相的色谱性能进行了研究。结果表明,该固定相对4类疏水性物质和无机阴离子均有较好的分离选择性和良好的峰对称性。进一步研究了所制备的Sil-VDI色谱柱对鸡蛋黄磷脂和肺腺癌细胞提取膜脂的分离效果,结果显示Sil-VDI色谱柱对2种磷脂样品均显示出了良好的分离能力。该文所制备的Sil-VDI色谱固定相合成方法简便,具有良好的分离分析应用潜能,后续工作会进一步研究该固定相在生物样品中的分离分析性能。     

基于二醛微晶纤维素功能化C18的反相/亲水色谱固定相的制备

通过十八烷基胺的氨基与二醛微晶纤维素的醛基共价键合,制备了基于二醛微晶纤维素(DMCC)官能化C₁₈的新型反相/亲水色谱固定相(C₁₈-DMCC/SiO₂),该色谱固定相被用于反相色谱(RPLC)和亲水相互作用色谱(HILIC)模式。C₁₈-DMCC/SiO₂色谱柱展现了良好的疏水选择性和芳香选择性,在反相色谱模式下可分离烷基苯和多环芳烃(PAHs)。苯胺类、酚类和糖苷类等极性化合物被用于评估该色谱柱在反相色谱模式下的极性选择性,商品C₁₈柱作对照柱,色谱评价结果令人满意。核酸碱基被用于评估C₁₈-DMCC/SiO₂色谱柱的亲水色谱性能。通过考察有机溶剂含量对分析物保留的影响,发现该新型色谱固定相具有反相/亲水色谱的典型特征。     

Acrylic-based high internal phase emulsion polymeric monolith for capillary electrochromatography

The use of high internal phase emulsion polymers (polyHIPEs) for CEC applications has remained relatively unexplored. A few reports exist in the literature for the preparation of similar structures. In this study, polyHIPEs having high porosity, and interconnected open-cell structure, were introduced and evaluated as stationary phase for CEC. The polyHIPE monolithic columns were prepared by the in situ polymerization of isodecylacrylate (IDA) and divinylbenzene (DVB) in the continuous phase of a high internal phase emulsion (HIPE). Due to its well-defined polyHIPE structure with interconnected micron size spherical voids, the columns synthesized with different initiator concentrations were successfully used for the separation of alkylbenzenes. Furthermore, the columns indicated a strong electroosmotic flow (EOF) without any additional EOF generating monomer probably due to the presence of ionizable sulfate groups coming from the water-soluble initiator used in the preparation of polyHIPE matrix. The best chromatographic performance in the separation of alkylbenzenes was achieved by using 70% ACN in the mobile phase with high column efficiency (up to 200 000 plates/m).     

Study of triacontyl-functionalized monolithic silica capillary column for reversed-phase capillary liquid chromatography

A novel stationary phase triacontyl-functionalized monolithic silica capillary column was successfully prepared for reversed-phase capillary liquid chromatography. The performance of the monolithic silica capillary column coated with triacontyl chain for the separation of alkylbenzenes, xylene isomers, polycyclic aromatic hydrocarbons, and mixture of α- and β-carotenes was studied, which was compared to that using the monolithic silica capillary column coated with octadecyl chain. The comparison results showed that triacontyl-functionalized monolithic silica capillary column would be a promising media to be used for the separation of isomeric solutes with long chain in reversed-phase capillary liquid chromatography.     

HPLC retention behaviors of poly-aromatic-hydrocarbones on Cu(II)-octabromotetrakis(4-carboxyphenyl)porphine derivatives-immobilized aminopropyl silica gels in polar and non-polar eluents

As one of approaches of developing novel HPLC stationary phases, we prepared Cu-octabromotetrakis(4-carboxyphenyl)porphine derivative-immobilized silica gels (Cu-OBTCPP(D)), and evaluated the availability of the resultant Cu-OBTCPP(D) as a stationary phase for separation of poly-aromatic-hydrocarbons (PAHs) and their related compounds. A Cu-OBTCPP(D) column was revealed to have an ability to separate simple PAHs and be useful as a stationary phase in both polar and non-polar eluents. The retention property of the Cu-OBTCPP(D) column was evaluated in various comparative experiments using commercially available columns. In comparison with 2-(1-pyrenyl)ethyl dimetylsilyl silica gel column (PYE column) regarding the retention behavior for PAHs etc., the Cu-OBTCPP(D) column showed stronger interactions involving pi electron in non-polar eluent than PYE column. In comparison with a pentabromobenzyloxy propylsilyl silica gel column (PBB column) regarding the influence of bromination, the Cu-OBTCPP(D) column was affected differently from the PBB column. In comparison with nitrophenylethyl silica gel column (NPE column) regarding the retention behavior for compounds having a dipole in a non-polar eluent, the Cu-OBTCPP(D) column showed electrostatic interactions such as dipole-dipole interaction equivalent to or larger than the NPE column.     

Porous layer open-tubular column with styrene and itaconic acid-copolymerized polymer as stationary phase for capillary electrochromatography–mass spectrometry

Enhancing the specific surface area of stationary phase is important in chromatographic science, especially in open-tubular column in which the coating only exists on the inner surface. In this work, a porous layer open-tubular (PLOT) column with stationary phase of styrene and itaconic acid-copolymerized polymer was developed. Thermal-initiated polymerization method with strategies like controlling the ratio of reaction reagents to solvents and reaction time, confinement by the narrow inner diameter of capillary were used for preparing the stationary phase with uniform structure and relatively thick layer. Due to the high separation efficiency and capacity, the PLOT column was used for capillary electrochromatography (CEC) separation of multiple groups of analytes like alkylbenzenes, phenyl amines, phenols, vanillins, and sulfonamides with theoretical plates (N) up to 1,54,845 N/m. In addition, due to high permeability of the CEC column and large electroosmotic flow mobility generated by abundant carboxyl groups in the coating material, the PLOT-CEC column was successfully coupled with mass spectrometry (MS) through a sheath flow interface. The developed PLOT-CEC-MS method was used for the analysis of antiseptics like parabens and herbicides like pyridines.     

Preparation of spherical silica hydroxyl-functionalized covalent organic polymer composites for mixed-mode liquid chromatography

Covalent organic polymers are an emerging class of amorphous microporous materials that have raised increasing concerns in analytical chemistry due to their unique structural and surface chemical properties. However, the application of covalent organic polymers as mixed-mode stationary phases in chromatographic separations has rarely been reported. Herein, novel spherical silica hydroxyl-functionalized covalent organic polymer composites were successfully prepared via a layer-by-layer approach. The structure and morphology of the materials were carefully characterized by elemental analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, Brunauer-Emmett-Teller, and contact angle measurements. Baseline separations of various alkylbenzenes, polycyclic aromatic hydrocarbons, and nucleosides and bases were achieved on the prepared stationary phase under reversed-phase/hydrophilic interaction mode. The column efficiencies of 23 853 and 36 580 plates/m were obtained for butylbenzene and uracil, respectively, and the relative standard deviation of the retention time for continuous injections was less than 1.38% (n = 10), suggesting satisfactory column efficiency and repeatability. Additionally, this novel stationary phase realized the complete separation of the endocrine-disrupting chemicals in river water. This work affords a new route for synthesizing covalent organic polymers-based mixed-mode stationary phase and further reveals their great potential in chromatographic separation.     

Simple interface of high-performance liquid chromatography-atomic fluorescence spectrometry hyphenated system for speciation of mercury based on photo-induced chemical vapour generation with formic acid in mobile phase as reaction reagent

In this study, we introduce an attractive stationary phase, poly(4-vinylpyridine)-grafted silica (VP(n)) for normal-phase high-performance liquid chromatography. The retention behavior of polycyclic aromatic hydrocarbons (PAHs) was investigated with VP(n) column under n-hexane/2-propanol mixture as mobile phase. Conventional octadecylated silica, aminopropyl-bonded silica, bare silica and poly(styrene)-grafted silica columns were used as reference columns. Extremely high retention factors were observed for PAHs but not for alkylbenzenes and distinct higher selectivity towards PAHs was observed for the detailed molecular shape such as planarity and aspect ratio. The reason for these results seems to be a multiple interaction effect including an inductive interaction between the pyridyl and aromatic rings.     

Octyl-functionalized hybrid silica monolithic column for reversed-phase capillary electrochromatography

Hybrid silica monolithic stationary phase functionalized with octyl groups was synthesized by a two-step acid/base-catalyzed hydrolysis/co-condensation of tetraethoxysilane (TEOS) and n-octyltriethoxysilane (C(8)-TEOS). The influences of determining factors in the sol-gel process such as the monomer ratio and water content on the monolith formation were systematically investigated. An increase in the TEOS/C(8)-TEOS ratio in the polymerization mixture shifted the pore size distribution towards smaller pore diameter with larger pore volume. The optimal TEOS/C(8)-TEOS volume ratio was found to be 90/50, under which condition the median pore diameter of the monolith was around 1.0 microm with pore volume of 3.25 cm(3)/g. The chromatographic characteristics of the monolithic column prepared with the optimized fabrication condition were studied. Some aromatic compounds including alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs) and phenols were successfully separated on the octyl-functionalized silica monolithic column with high column efficiency up to 180,000 plates/m.     

Development of a new C14 monolithic silica column containing embedded polar groups for pressurized capillary electrochromatography

Monolithic columns have been prepared with a novel bonded silica stationary phase, tetradecylamine bonded silica (TDAS), and used in pressurized capillary electrochromatography (pCEC). The monolithic silica column matrix was prepared by a sol-gel process and then chemically modified with the spacer (3-glycidoxypropyl)trimethoxysilane and tetradecylamine. The introduced embedded polar amine groups dominated the charge on the surface of the monolithic stationary phase and generated an EOF from cathode to anode under acidic conditions. The tetradecyl hydrophobic chains in TDAS provide chromatographic interactions. The chromatographic characteristics of the prepared monolithic column were studied. Some aromatic compounds including alkylbenzenes, aromatic hydrocarbons, phenols, and anilines were successfully separated on the TDAS monolithic column in pCEC mode. As expected, the TDAS monolithic stationary phases exhibit typical reversed-phase electrochromatographic behavior toward neutral solutes due to the introduced tetradecyl groups. Hydrophobic as well as electrophoretic migration processes within the monoliths were observed in the separation of basic anilines. Symmetrical peaks can be obtained for anilines because the embedded polar amine groups on the surface can effectively shield the adsorption of positively charged analytes onto the stationary phase.     

Gas chromatographic analysis of high-molecular-mass polycyclic aromatic hydrocarbons II. Polycyclic aromatic hydrocarbons with relative molecular masses exceeding 328

Three columns were used for the gas chromatographic analysis of polycyclic aromatic hydrocarbons (PAHs) with relative molecular masses (M_r) up to 450. Two of the columns were commercially available, coated with a 50% methyltrifluoropropyl-substituted polysiloxane a 5% diphenyl-substituted methylpolysiloxane. The third column was laboratory made, coated with a biphenyl-substituted silarylene-siloxane copolymer. All three columns were utilized for the analysis of high-M_r PAHs as regards both thermal stability of the stationary phases, i.e., low bleeding rate, and chromatographic efficiency. The column coated with a trifluoropropyl-substituted stationary phase showed, however, a low separation efficiency, possibly owing to low solute stationary phase compatibility. The biphenyl-substituted stationary phase, on the other hand, showed a very high separation efficiency, but the retention of the PAHs was significantly higher on this column compared with the other two, leading to the demand for higher oven temperatures. Different retention mechanisms were observed on these columns, as shown by differences in the retention indices of the PAHs measured in a system using PAHs as retention index markers. A comparatively faster elution of non-planar PAHs was observed on the columns coated with the trifluoropropyl-substituted stationary phase and the biphenyl-substituted stationary phase compared with the column coated with the 5% diphenyl-substituted polymer. The usefulness of the columns for separations of high-M_r PAHs is demonstrated by gas chromatograms of carbon black extracts and a coal tar extract standard reference material.     

Incorporation of graphene oxide nanosheets into boronate‐functionalized polymeric monolith to enhance the electrochromatographic separation of small molecules

Graphene oxide (GO) nanosheets were incorporated into an organic polymer monolith containing 3‐acrylamidophenylboronic acid (AAPBA) and pentaerythritol triacrylate (PETA) to form a novel monolithic stationary phase for CEC. The effects of the mass ratio of AAPBA/PETA, the amount of GO, and the volume of porogen on the morphology, permeability and pore properties of the prepared poly(AAPBA‐GO‐PETA) monoliths were investigated. A series of test compounds including amides, alkylbenzenes, polycyclic aromatics, phenols, and anilines were used to evaluate and compare the separation performances of the poly(AAPBA‐GO‐PETA) and the parent poly(AAPBA‐co‐PETA) monoliths. The results indicated that incorporation of GO into monolithic column exhibited much higher resolutions (>1.5) and column efficiency (62 000 ～ 110 000 plates/m for toluene, DMF, formamide, and thiourea) than the poly(AAPBA‐co‐PETA). The successful application in isocratic separation of peptides suggests the potential of the GO incorporated monolithic column in complex sample analysis. In addition, the reproducibility and stability of the prepared poly(AAPBA‐GO‐PETA) monolith was assessed. The run‐to‐run, column‐to‐column and batch‐to‐batch reproducibilities of this monolith for alkylbenzenes’ retention were satisfactory with the RSDs less than 1.8% (n = 5), 3.7% and 5.6% (n = 3), respectively, indicating the effectiveness and practicability of the proposed method.     

Photo‐polymerized lauryl methacrylate monolithic columns for CEC using lauroyl peroxide as initiator

Lauryl methacrylate (LMA)‐ester based monolithic columns photo‐polymerized using lauroyl peroxide (LPO) as initiator were prepared, and their morphological and CEC properties were studied. The composition of the polymerization mixture (i.e. ratios of monomers/porogenic solvents, 1,4‐butanediol/1‐propanol and LMA/crosslinker) was optimized. The morphological and chromatographic properties of LMA columns were evaluated by means of SEM pictures and van Deemter plots of PAHs, respectively. The polymerization mixture selected as optimal provided a fast separation of a mixture of PAHs with excellent efficiencies (minimum plate heights of 8.9–11.1 μm). Satisfactory column‐to‐column (RSD<4.5%) and batch‐to‐batch reproducibilities (RSD<6.3%) were achieved. The LMA columns photo‐polymerized with LPO were compared with those prepared with AIBN. Using PAHs, alkylbenzenes and basic compounds for testing, the columns obtained with LPO gave the best compromise between efficiency, resolution and analysis time.     

Temperature optimization for the separation of PAHs on micropacked LC ODS columns

The effect of column temperature on the separation of the sixteen polycyclic aromatic hydrocarbons (PAHs) of mixture SRM 1647a of the US Environmental Protection Agency has been studied on different micropacked ODS columns. Isothermal temperature optimization was successfully used for complete separation of the PAHs on a polymeric ODS stationary phase, whereas temperature programmed conditions were selected for separation on a monomeric ODS stationary phase.     

基于聚倍半硅氧烷微球的亲水/反相混合模式色谱填料的制备与评价

亲水/反相混合模式色谱应用广泛,但pH使用范围有限,不利于碱性药物的分离。该工作利用巯基-烯基点击化学合成了单分散多孔的半胱氨酸改性乙烯基功能化聚甲基倍半硅氧烷(C-V-PMSQ)微球。元素分析表明半胱氨酸成功键合在微球表面。C-V-PMSQ微球为介孔结构,单分散性好且具有优良的化学稳定性。以几种常见的核苷和核酸碱基作为测试样品,考察其色谱保留行为,溶质的保留因子随流动相中水相含量的变化呈现典型的U型曲线,表明C-V-PMSQ固定相具有亲水/反相的双重保留特征。使用该固定相可以分离苯的同系物及一系列亲水性与疏水性化合物。另外在高碱性流动相条件下利用亲水和反相模式成功分离了中药苦参中的3种主要活性成分,表明它在分离碱性药物方面具有较大的优势。     

Preparation and Evaluation of 1,3-alternate 25,27-Bis-[p-nitrobenzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene-bonded Silica Gel Stationary Phase for LC

A novel 1,3-alternate 25,27-bis-[p-nitrobenzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel stationary phase has been prepared and used for separating various selected analytes by HPLC. The effect of organic modifier and pH of the mobile phase on retention and selectivity were studied using aromatic positional isomers as an example. Application examples have been provided for separation of alkylbenzenes, PAHs, xanthine derivatives, and purine and pyrimidine bases. A selectivity comparison of the novel phase versus CalixBz and Backerbond PhenylEthyl phases has been performed.