Applicability of two-membrane reactors for reversible gas phase reaction. Effects of flow patterns and inerts

The objective of this study is a comparative analysis of single and two-membrane reactor performances for isothermal reversible gas phase reaction. The effects of flow patterns (ideal mixing, cocurrent and countercurrent plug flow) and the presence of inert components were investigated. It is shown by simulation that for the pure reactant feed in absence of inerts, the performance of a two-membrane reactor is not significantly affected by the flow patterns, providing the pressure ratio is kept close to zero. Concerning the conversion efficiency in the case when the reactant is the slowest permeating component, the advantage of a two-membrane reactor is evident, it being least significant for countercurrent plug flow. In the presence of inerts in the separation zone, the advantage of a two-membrane reactor is maintained, while it is diminished by increasing inert flow rate in the reaction zone.     

Separation of helium and hydrocarbon mixtures by a two-membrane column

The permeabilities to pure gases can be directly used in the calculation of mixed gas permeation through a rubbery membrane (silicone rubber), but the permeabilities of cellulose acetate membranes to mixed gases are considerably affected by the presence of hydrocarbons. The efficiency of separation increases with decreasing pressure ratio and reaches a maximum when the pressure ratio becomes zero. The enrichment of the less permeable gas can be easily achieved in a stripper. Combining two strippers made out of two different membranes, highly concentrated products (99%) are continuously obtained at both ends of the column. As a result, the overall separation factors are greatly increased.     

Column extraction chromatography of non-volatile platinum metals

Mixtures of Pd(II)-Pt(IV)-Ir(IV) and of Rh(IV)-Pd(II)-Pt(IV)-Ir(IV) have been separated by column chromatography on silica treated with a tri-n-octylammonium salt, by three-step elution with mixtures of hydrochloric acid (2.25M). The optimal conditions for separation were identified from preliminary paper-chromatographic data and the results of column experiments for the individual metals. Single bands for each non-volatile platinum metal were found for the proposed chromatographic system and satisfactory recoveries of single metals from mixtures were obtained. The simple method proposed requires only one column for the separation, which can be repeated at least three times on the same column. The separation needs about 2 hr elution time.     

Liquid chromatographic separation of proteins derivatized with a fluorogenic reagent at cysteinyl residues on a non-porous column for differential proteomics analysis

A wide-pore (30 nm) reversed-phase column (Intrada WP-RP, particle size 3 μm) was recently utilized for protein separation in differential proteomics analysis with fluorogenic derivatization-liquid chromatography-tandem mass spectrometry (FD-LC-MS/MS), and exerted a tremendous effect on finding biomarkers (e.g., for breast cancer). Further high-performance separation is required for highly complex protein mixtures. A recently prepared non-porous small-particle reversed-phase column (Presto FF-C18, particle size: 2 μm) was expected to more effectively separate derivatized protein mixtures than the wide-pore column. A preliminary experiment demonstrated that the peak capacity of the former was threefold greater than that of the latter in gradient elution of a fluorogenic derivatized model peptide, calcitonin. The FD-LC-MS/MS method with a non-porous column was then optimized and applied to separate liver mitochondrial proteins that were not efficiently separated with the wide-pore column. As a result, high-performance separation of mitochondrial proteins was accomplished, and differential proteomics analysis of liver mitochondrial proteins in a hepatitis-infected mouse model was achieved using the FD-LC-MS/MS method with the non-porous column. This result suggests the non-porous small-particle column as a replacement for the wide-pore column for differential proteomics analysis in the FD-LC-MS/MS method.     

GC with LC-like packed capillary columns

Capillary columns of 0.3–0.35 mm internal diameter and 0.3–7.7 m length, packed with 3 to 30 μm octadecylsilica stationary phases as used for liquid chromatography, were applied to gas chromatographic separation of low boiling hydrocarbons. Van Deemter plots for these columns showed the optimum column efficiency to occur at linear velocities of 4–5 cm/s. A short column was applied to the rapid separation of components of a natural gas and impurities in standard gases, while a long column was applied to the separation of complex mixtures.     

Ligand Exchange Gas Chromatography on PTFE Open Tubular Columns

Two kinds of capillary columns were prepared and tested as the stationary phases of ligand exchange gas chromatographic separation of dialkyl sulfides. The PTFE column wall-coated with silane-DTC-Cu but without the addition of silicone exhibits significantly better selectivity towards dialkyl sulfides than a column wall-coated with 10% silane-DTC-Cu in silicone. With the first column connected to a microsample injection valve and a microsample loop, the quantitative determination of dialkyl sulfides can be performed. The column also shows great promise for the separation of dialkyl sulfide-hydrocarbon mixtures.     

High-Pressure Ion Exchange Chromatography as Applied to the Separation of Complex Biochemical Mixtures

Interest in liquid column chromatography, including ion exchange chromatography, as a separation method has increased markedly in the past few years. Numerous new automated analytical techniques, as well as applications for preparative or production-scale separations, have been developed. This has been particularly true in the areas pertaining to separation and analysis of biochemical mixtures such as physiologic fluids. The recent trend in ion exchange chromatography has been toward achieving two goals: high-resolution analysis in the case of complex mixtures, and high-speed separation when simpler mixtures are involved. In either case, the use of small-diameter ion exchange resin particles coupled with high flow rates (and, in some cases, long columns) requires operation at relatively high column inlet pressures, since the pressure drop through the ion exchange column is dependent on factors such as resin particle size, flow rate, and column length.     

Fast temperature programming on a stainless-steel narrow-bore capillary column by direct resistive heating for fast gas chromatography

A direct resistive-heating fast temperature programming device for fast gas chromatography was designed and evaluated. A stainless-steel (SS) capillary column acted both as a separation column and as a heating element. A fast temperature controller with the deviation derivative proportional-integral-derivative (DDPID) control algorithm, which was suitable for ramp control using ramp-to-setpoint function, was used to facilitate the fast pulse heating. The SS resistive-heating column can generate linear temperature ramps up to 10 degrees C/s and can re-equilibrium from 250 degrees C down to 50 degrees C within 30s. With n-alkanes as the test analytes, the relative standard deviations (RSDs) of retention time were between 0.19 and 0.59% and the RSDs of their peak areas were less than 4% for all but one. The results indicated that this technique could be used for both qualitative and quantitative analysis. Phenolic and nitroaromatic compounds were also analyzed by using the SS resistive-heated system. The combination of a short narrow-bore SS column and rapid heating rates provides sufficient separation efficiency for relatively simple mixtures at drastically reduced analysis time. The total analysis time including equilibration time was less than 2 min for all test mixtures in this study.     

Liquid chromatographic retention and separation of phenols and related aromatic compounds on reversed phase columns

Summary Isocratic column liquid chromatographic systems with UV absorbance detection at 280 nm have been developed for the separation of 29 phenolics and related compounds.The selectivity was investigated on silica-, carbon- and polymer-based separation columns for the separation of phenolic type of components. The effects of various acetonitrile/buffer mixtures, and pH of the mobile phase, and their impact on the retention of the phenols was assessed. Tables of retention times on the four columns for the 29 phenols with two different acetonitrile/buffer mixtures, together with the retention times at three pHs from 6.5 to 2.3 with varying levels of organic modifier on the LiChrospher RP 18 column are presented.As an application, the analysis of real river water samples from the Ebro river is described using a solid phase extraction step prior to injection into the chromatographic system.     

以二甲亚砜/正十二醇为二元致孔剂的新型苯乙烯-二乙烯苯毛细管整体柱的制备与表征

首次以二甲亚砜/正十二醇为二元致孔剂,苯乙烯为单体,二乙烯苯为交联剂,过氧化苯甲酰为引发剂,通过原位聚合反应制备了苯乙烯-二乙烯苯聚合物型毛细管整体柱。结果表明,苯乙烯∶二乙烯苯∶二甲亚砜∶正十二醇的体积比为18.7∶15.3∶13.2∶52.8,即二甲亚砜占致孔剂的比例为20%,交联度为45%,致孔剂含量为66%为最优配比。所合成的整体柱实现了反相色谱模式下对小分子苯系物与生物大分子蛋白的快速分离。其中蛋白分离实验的流速达到104μL·min-1,线速度约为12 mm·s-1,而常规色谱柱的线速度为1~2 mm·s-1。该整体柱的渗透性好,可用于物质的高速分离,若对其进行化学修饰,有望用于其它色谱分离模式。     

Separation of natural product using columns packed with Fused‐Core particles

Three HPLC columns packed with 3 μm, sub‐2 μm, and 2.7 μm Fused‐Core (superficially porous) particles were compared in separation performance using two natural product mixtures containing 15 structurally related components. The Ascentis Express^TM C18 column packed with Fused‐Core particles showed an 18% increase in column efficiency (theoretical plates), a 76% increase in plate number per meter, a 65% enhancement in separation speed and a 19% increase in back pressure compared to the Atlantis T3^TM C18 column packed with 3 μm particles. Column lot‐to‐lot variability for critical pairs in the natural product mixture was observed with both columns, with the Atlantis T3 column exhibiting a higher degree of variability. The Ascentis Express column was also compared with the Acquity^TM BEH column packed with sub‐2 μm particles. Although the peak efficiencies obtained by the Ascentis Express column were only about 74% of those obtained by the Acquity BEH column, the 50% lower back pressure and comparable separation speed allowed high‐efficiency and high‐speed separation to be performed using conventional HPLC instrumentation.     

Optimization of comprehensive two dimensional gas chromatography-flame ionization detection-quadrupole mass spectrometry for the separation of octyl- and nonylphenol isomers

In the present work, the separation of complex nonylphenol technical mixtures has been optimized using comprehensive two-dimensional gas chromatography coupled with a flame ionization detector and quadrupole mass spectrometer (GC×GC-qMS), using valve-based modulator. The optimization of GC×GC-qMS has been carried out using experimental designs and the optimal separation was obtained at the following conditions: 1st column flow: 1mL/min; 2nd column flow: 17.75 mL/min, oven temperature ramp: 1°C/min, modulation period: 1.5s and discharge time: 0.12s. These values have been used to determinate the previously synthesized 22OP, 33OP, 363NP and 22NP isomers in two different nonylphenol technical mixtures. Percentages obtained were as follows: 4.86% and 0.59% for 22OP, 4.91% and 2.82% for 33OP, 11.79% and 7.71% for 363NP and 2.28% and 1.98% for 22NP, in Fluka and Aldrich mixtures, respectively. The values obtained for NP isomers are in good agreement with the literature.     

A Novel Approach to Reversed-Phase Preparative High-Performance Liquid Chromatography of Peptides

Abstract

In this study, we describe a novel approach to preparative liquid chromatography which takes advantage of the different relative hydrophobicities of components of a sample mixture, so that when a column is optimally loaded with an aqueous solution of the sample mixture, there is competition among the sample components for the adsorption sites on the hydrophobic stationary phase. The more hydrophobic components compete more successfully for these sites than more hydrophilic components, which are displaced and immediately eluted from the column. Thus, the major separation takes place in water. Subsequent treatment with an aqueous organic modifier is only required to wash retained components off the column and takes no part in the major separation process. This approach was applied to the preparative purification of mixtures of closely-related peptides, representing the crude peptide mixtures typically obtained from solid-phase peptide synthesis. The excellent separation profiles and high yields of pure peptide products on analytical columns reported in this study demonstrate that this methodology has great potential for preparative separation of a major component from hydrophilic and/or hydrophobic impurities.     

Comprehensive two-dimensional capillary supercritical fluid chromatography in stop-flow mode with synchronized pressure programming

A comprehensive two-dimensional capillary supercritical fluid chromatography method was developed. The interface consisted of a ten-port valve, a capillary trap and two fused silica restrictors. The primary column was operated in stop-flow mode: the flow in the primary column was stopped during the separation of the second dimension. The pressure of the system was controlled with a single pump. The pressure program was synchronized with the sampling: the pressure was only ramped up during the sampling time, when the primary column effluent was transferred from the first dimension to the trap, and was maintained constant during the second-dimension separation. All of the operations were automated using in-house software. The separation characteristics of the present system can be readily regulated by changing the size of the restrictors and/or the programmed pressure rate. The use of synchronized pressure programming allowed the sampling duration and/or the second-dimension separation time (and therefore, the total analysis time) to be changed without affecting the separation pattern. Widely different selectivities were attained depending on the combination of the three columns with different polarities (such as the nonpolar DB-1, the medium-polarity DB-17 and the polar DB-WAX columns) used. The present system afforded improved separation and identification capabilities for analytes in complex mixtures.     

Separation characteristics of fatty acid methyl esters using SLB-IL111, a new ionic liquid coated capillary gas chromatographic column

The ionic liquid SLB-IL111 column, available from Supelco Inc., is a novel fused capillary gas chromatography (GC) column capable of providing enhanced separations of fatty acid methyl esters (FAMEs) compared to the highly polar cyanopropyl siloxane columns currently recommended for the separation of cis- and trans isomers of fatty acids (FAs), and marketed as SP-2560 and CP-Sil 88. The SLB-IL111 column was operated isothermal at 168°C, with hydrogen as carrier gas at 1.0 mL/min, and the elution profile was characterized using authentic GC standards and synthetic mono-unsaturated fatty acids (MUFAs) and conjugated linoleic acid (CLA) isomers as test mixtures. The SLB-IL111 column provided an improved separation of cis- and trans-18:1 and cis/trans CLA isomers. This is the first direct GC separation of c9,t11- from t7,c9-CLA, and t15-18:1 from c9-18:1, both of which previously required complimentary techniques for their analysis using cyanopropyl siloxane columns. The SLB-IL111 column also provided partial resolution of t13/t14-18:1, c8- from c6/c7-18:1, and for several t,t-CLA isomer pairs. This column also provided elution profiles of the geometric and positional isomers of the 16:1, 20:1 and 18:3 FAMEs that were complementary to those obtained using the cyanopropyl siloxane columns. However, on the SLB-IL111 column the saturated FAs eluted between the cis- and trans MUFAs unlike cyanopropyl siloxane columns that gave a clear separation of most saturated FAs. These differences in elution pattern can be exploited to obtain a more complete analysis of complex lipid mixtures present in ruminant fats.     

Construction and development of a new single-column simulated moving bed system on the laboratory scale

Simulated moving bed (SMB) chromatography combines high productivity and high purities with reduced buffer consumption. We have developed a laboratory scale single column SMB (SC-SMB) unit with all four separation zones in one column. Distributors embedded within the chromatographic medium allow introduction and withdrawal of liquid between the zones. This single column unit exhibits homogenous packing in all zones, reduced headspace, less complex tubing, fewer valves, and almost undisturbed plug flow between the separation zones. The separation performance of the column was investigated with two different binary model mixtures. Furthermore, the SC-SMB unit is operated with a modified AKTA Explorer workstation, which has been specifically developed for the handling of biological fluids.     

原位合成分子筛膜毛细管色谱柱的研制

吸附型多孔层毛细管柱既耐高温又对气体及烃类异构体有选择性，同时又具有毛细管色谱快速、高效等优点，是解决难分离组分的重要柱型．常用作气一固吸附色谱固定相的有强极性的硅、中极性的氧化铝、非极性的碳质及特殊吸附作用的分子筛．其中分子筛以其独特的吸附作用，在永久性气体和烃类碳数族组成分析中有重要地位．Pruecell和Soulages[1，2]等制备了涂渍型5A和13X型分子筛的毛细管柱，对低碳烃类化合物显示了良好的分离能力，分析柱温较填充柱降低约100℃．邹乃忠等[3～5]也先后制备了分子筛层的毛细管柱用来作直馏汽油的分析．由于通…     

Separation of coumarins from Archangelica officinalis in high-performance liquid chromatography and thin-layer chromatography systems

Complex, multicomponent mixtures are difficult to separate in a single chromatographic run. Therefore, the possibility to separate twelve coumarins from Archangelica officinalis was studied by combining a HPLC and a TLC system. HPLC optimized by the use of DryLab for Windows software was performed on RP-18 column and TLC was performed on silica plates. Fractions from the RP column were evaporated, applied on silica plate and developed in non-aqueous solvent. Possibilities of complete separation of investigated coumarins were discussed in RP and NP systems. The result of their complete separation was presented by HPLC chromatograms, DryLab simulated chromatograms and a video scan of TLC plate.     

Separation of low-boiling hydrocarbons by capillary gas chromatography with glass columns treated with hot alkaline solution

Summary Soda-lime glass-capillary columns treated with 1M sodium hydroxide at 40–60°C for two days were employed for the gas chromatographic separation of low-boiling hydrocarbons. A 70.5 m×97 m I.D. column produced 780,000 to 930,000 theoretical plates for early-eluting components. Use of steam-doped carrier gas improved peak shape and column efficiency. The system was successfully applied to the separation of complex mixtures.     

Electrochromatographic performance of conventional and polar-embedded C16 silica monolithic stationary phases

A novel monolithic silica column that has a polar‐embedded amide‐secondary amine group linking with C16 functionality for RP‐CEC is described. The amide‐secondary aminealkyloxysilane was synthesized by the reaction of 3‐(2‐aminoethylamino) propyltrimethoxysilane with hexadecanoyl chloride. Then, the silylant agent was bonded to the silica monolith matrix to produce hexadecanamide‐secondary amine bonded silica (HDAIS) monolithic column. The electrochromatographic performance of HDAIS monolithic column for the separation of neutral, basic and polar solutes was studied, which was compared to that using the hexadecyl bonded silica monolithic column. The HDAIS monolithic column displayed reduced hydrophobic retention characteristics in the separation of five hydrophobic n‐alkylbenzenes and four polar phenols when compared to the hexadecyl bonded silica monolithic column. A very much reduced silanol activity of HDAIS monolithic column was observed in the separation of test basic mixture including four aromatic amines, atenolol and metoprolol with 10 mM borate buffer (pH 7.5) containing 30% v/v ACN as the mobile phase. The comparison results indicate good performance for both polar and basic mixtures on HDAIS monolithic column in RP‐CEC, and also show promising results for further applications.