Adjusting selectivity in liquid chromatography by use of the thermally tuned tandem column concept

In this study, we propose the novel "thermally tuned tandem column (T3C)" concept for the optimization of selectivity in LC by continuous adjustment of the stationary phase. Two columns with distinctly different chromatographic selectivities (e.g., polybutadiene- and carbon-coated zirconia) are serially coupled and independently temperature-controlled. Selectivity is "tuned" by adjusting the individual temperatures of the two columns. The effect of changing column temperature is quite analogous to changing the relative column lengths, thereby altering the relative and absolute contribution each column makes to the overall retention time in T3C. The distinct selectivity differences between polybutadiene- and carbon-coated zirconia as well as the extraordinary thermal stability of zirconia-based phases (thermally stable to 200 degrees C) allow us to tune the overall chromatographic selectivity over a very substantial range. We have developed a simplified useful model, which characterizes retention and selectivity for the T3C system as a function of the two column temperatures. The model is in good agreement with the experimental results. We also describe a simple computer-assisted optimization strategy based on the window diagram method, which facilitates the optimization of the T3C system with only four or five initial runs.     

Separation of barbiturates and phenylthiohydantoin amino acids using the thermally tuned tandem column concept

There are many more choices of column type than of eluent type for method development in reversed-phase liquid chromatography. It is common to switch between different column types or between the same type from different suppliers to achieve the desired separations. The key difficulty in modulating band spacing by adjusting the column type is that it is a discontinuous, "hit or miss" proposition. The thermally tuned tandem column (T3C) concept effectively solves this problem by connecting two columns in series and independently controlling the two column temperatures. The columns are chosen to have distinctively different chromatographic selectivities (band spacing), so that the unresolved peaks on one column are separated by the other. The optimized separation in the T3C is achieved by simultaneously tuning the two column temperatures. In this study, we used the T3C combination of a carbon and a conventional bonded phase for the separation of barbiturates and phenylthiohydantoin amino acids (PTH-amino acids). Good peak shapes and comparable retention times were observed on the two phases at room temperature. The selectivities on the two phases are quite different. Baseline separations were easily achieved with the T3C set although neither column could individually resolve all the peaks. We further compared the separation of barbiturates optimized by the T3C approach with that optimized by adjusting the mobile phase. We found that T3C gave a better separation. We believe that the T3C combination of a carbon phase and a bonded conventional reversed-phase material provides a powerful and general method to optimize the separation of various mixtures.     

Separation of selected basic pharmaceuticals by reversed-phase and ion-exchange chromatography using thermally tuned tandem columns

The separation of basic pharmaceuticals is usually performed on C8 or C18 bonded silica supports. Silanolphilic interactions between basic analytes and surface silanol groups often lead to tailed peaks, poor efficiency, and irreproducible retention times. To solve these problems, many new types of silica-, zirconia-, and polymer-based columns, which provide unique selectivities, improved stability at high pH, or both, have been developed for the analysis of basic compounds. The essence of method development for the chromatographic analysis of basic compounds is to choose a system in which the band spacing can be varied dramatically, quickly, and conveniently while minimizing the tailing due to silanolphilic interactions. The thermally tuned tandem column (T3C) approach has been shown to provide an effective way to adjust stationary-phase selectivity for nonionic compounds. In this study, a tandem combination of an octadecylsilane (ODS) and a polybutadiene-coated zirconia (PBD-ZrO2) phase was used to separate nine antihistamines. Selectivity is tuned by independently adjusting the isothermal temperatures of the two columns. We found dramatic differences in the retention factors, elution sequences, and band spacing for the above set of basic drugs on the two types of columns. The T3C model has been used successfully to locate the optimal temperatures based on only four exploratory runs. The nine antihistamines were baseline separated on the tandem column combination even though they could not be separated on the individual phases. The effect of the buffer concentration on retention of the basic antihistamines was also studied. We conclude that cation-exchange interactions predominate on the PBD-ZrO2 phase, while reversed-phase interactions are more important on the ODS phase. Interestingly, an increase in column temperature causes a significant increase in the retention on the ODS column and a decrease of retention on the PBD-ZrO2 column. This can be explained by the change in the analyte's degree of ionization with temperature. The T3C combination of silica- and zirconia-based RPLC columns is demonstrated to be a powerful approach for the separation of this mixture of basic analytes.     

Complete enantiomeric separation of phenylthiocarbamoylated amino acids on a tandem column of reversed and chiral stationary phases

The enantiomeric separation of phenylthiocarbamoyl derivatives of amino acids (PTC-AAs) was studied on a series of reversed phase HPLC columns coupled to the chiral phase HPLC columns. First, the five chiral phases (native, 0.2, 3.3, 7.5 and 16.9 phenylcarbamoylated/β-cyclodextrins, Ph/CD) were newly prepared by modification of β-cyclodextrin with phenyl isocyanate and were examined for the enantiomeric separation of PTC-AAs. Among them, the 3.3Ph/CD phase gave the best enantiomeric separation (α ≥ 1.04). However, the separation of the individual PTC-AAs was not sufficient. Next, these separations were investigated on various reversed phase HPLC columns, and octyl silica was selected in terms of the suitability of the mobile phase adopted for the enantiomeric separation mentioned above. The effects of the column temperature, the ion-pairing reagent, and the final content of methanol were also studied on the tandem column of octyl silica and the 3.3Ph/CD phase. Under the best conditions (100 mM ammonium acetate (pH 6.5) containing 1 mM butanesulfonate with 0-40% methanol as the mobile phase), all the individual PTC-AAs were well separated within 150 min. The applicability of the method was demonstrated by the sequence/configuration analysis of a peptide containing a d-amino acid ([d-Thr(2)]leucine enkephalin-Thr).     

Fabrication of stem cell chip with peptide nanopatterned layer to detect cytotoxicity of environmental toxicants

A stem cell chip with peptide nanopatterned layer was fabricated to detect the effects of environmental toxins on human neural stem cells (HB1 x F3) electrochemically. The cell chip was recently developed as in vitro monitoring tool for determining the cell viability simply and rapidly compared to the conventional methods. However, cell chip composed of neural stem cells have not been reported due to the difficulties for maintaining its stemness and cell attachment on the artificial electrode surface, which is critical for sensitive detection of cell viability electrochemically. In this study, we fabricated peptide nanopatterned layer on gold electrode for increasing the affinity between the stem cell and an artificial electrode surface by self-assembly technique. After the confirmation of fabricated nanopatterned surface, neural stem cells were immobilized on chip surface and the viability was measured by electrochemical method. Thereafter, neural stem cells were treated with two kinds of common environmental toxins, and the intensities of reduction peak obtained by cyclic voltammetry (CV) were decreased with the increase of concentrations of environmental toxins. These electrochemical results were validated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Our newly developed stem cell chip can be used as useful label-free analysis tool for detecting drug effects or for assessing the toxicity electrochemically.     

A tandem column ensemble with an atmospheric pressure junction-point vent for high-speed GC with selective control of peak-pair separation

A series-coupled (tandem) ensemble of two capillary GC columns using different stationary phases and a pneumatically actuated low-volume valve connecting the column junction point to an atmospheric-pressure vent line is used to adjust the ensemble separation of selected pairs of target compounds. The valve is normally closed, and the pressure at the column junction point assumes the value that would occur in the absence of any other connections. The valve can be opened for brief periods of time, thus producing pulses of atmospheric pressure at the column junction point. If a component pair is separated by the first column but coelutes from the column ensemble, the ensemble separation can be increased if a pulse occurs when one of the components has migrated across the column junction but the second component is still on the first column. All of the mixture components that are on the same column during the time that the valve is open (pulse duration) will be shifted to either larger or smaller retention times, but the pattern of peaks (elution order) for these components from the column ensemble will be relatively unaffected by the pressure pulse. Multiple pulses can be used to enhance the separation of different component pairs, which sequentially reach the column junction point. Performance of the valve-operated system is described. Time-of-flight mass spectrometry with time-array detection is used to examine the effects of pulse duration on the separation achieved for different component pairs.     

Detection of the effect of environmental toxicants on the synthetic peptide modified neural cell chip

A cell based chip was designed to differentiate and to detect the effects of environmental chemicals on the neurite outgrowth in PC12 cell. To fabricate platform of cell chip, gold surfaces were modified by RGD based synthetic oligopeptide. Nanoscale controlled self-assembled peptide layer was investigated by Atomic Force Microscopy (AFM). On the fabricated cell chip, PC12 cell was immobilized and the differentiation of neurite outgrowth in PC12 cells was done by neurite growth factor (NGF). Differentiation of PC12 cell was confirmed by immunofluorescence study. Further the differentiation and the length of neurite was confirmed by confocal microscopy study. Voltammetry behavior of the neurite induced PC12 and the electrochemical behavior of the environmental toxicants effect on the neurite outgrowth was measured by cyclic voltammetry (CV). Self-assembled layer mediated cell immobilization technique and voltammetric signal analysis system can be applied to construct the neural cell chip for the detection of large number of environmental toxins and various neurotoxicants.     

多套空分设备综合优化运行的实践与探索

结合南钢制氧厂的成功经验,从自动变负荷技术的运用、空分设备处于经济性较高的负荷段运行、优化开/停车时的操作、氮压机一拖二模式运行、提高氩提取率、减少自用氮气消耗和液化装置合理运行7方面,论述了多套空分设备综合优化运行的实践。     

Application of disclination concept to solid structures

Disclinations together with dislocations represent a class of linear defects in solids. Disclinations are characterized by typical singularities and the property of multi-value of the fields of displacement and rotation associated with the defects. We present an introduction to and overview of recent achievements of the disclination approach in physics and mechanics of solid structures. In the development of F.R.N. Nabarro ideas, the use of the disclination approach in materials science is demonstrated. The following milestones of the disclination concept are given and discussed: (i) definitions and designations for Volterra dislocations, Frank (rotation) vector of a disclination, wedge and twist disclinations; (ii) geometry of disclinations in structure-less and crystalline solids; (iii) the properties of screened low-energy disclination configurations, e.g. loops, dipoles, defects at the vicinity of a free surface, including the methods and results of calculation of their elastic fields and energies. Then using the properties of screened disclinations a number of qualitative and quantitative models for the structure formation and evolution in plastically deformed materials, is considered. Disclination theory of grain boundaries and their junctions in conventional polycrystals is presented. The bands with misorientated crystal lattice in metals and other materials are described as a result of partial wedge disclination dipole motion. Disclination approach is applied to the study of work-hardening at large strains. For nanocrystals, disclination approach allows to explain the peculiarities of the flow stress dependence on the grain size. The contribution of disclinations to relaxation of mechanical stresses in lattice mismatched thin layers placed on the bulk substrate is examined and linked to the appearance of domain patterns. Finally, disclination models for the structure and properties of nanoparticles are presented. These models treat the pentagonal symmetry of micro- and nanoparticles and nanorods of materials with FCC crystal structure and explain stability and relaxation phenomena in such pentagonal objects.     

膜分离技术在染料行业中的应用

介绍了近年来膜分离技术在染料行业中的应用现状 ,在生产方面 ,膜分离技术作为清洁生产工艺取代传统的生产工艺已实际可行 ,在废水治理方面 ,用膜法处理染料废水尚处在研究应用阶段     

Application of the multi-level current reinjection concept to HVDC transmission

The self-commutating multilevel current reinjection (MLCR) reduces the converter current waveform to zero during the valves commutations and, thus, removes the converter dependence on line commutation. This property provides the conventional thyristor converter with the same flexibility as the self-commutating multi-level schemes in terms of reactive power control and harmonic elimination. This paper describes the structure and control of a current source HVDC transmission scheme using MLCR converters. Extensive EMTDC simulation is carried out to demonstrate the improved controllability of the proposed HVDC configuration     

热致相分离法制备共聚物微孔膜研究进展

阐述了热致相分离法(TIPS)制备微孔膜的研究现状。介绍了混合共聚物膜及共聚物微孔材料的制备条件及其性能,包括等规聚丙烯/聚丁烯、聚偏氟乙烯/聚甲基丙烯酸甲酯、乙烯/三氟氯乙烯共聚物、乙烯/丙烯酸、乙烯/乙烯醇和乙烯/乙烯醇/乙烯缩丁醛等,并对TIPS方法制备共聚物微孔膜的研究方向进行展望。     

在线分析在空分中的应用

介绍了空气分离中典型的分析点及在线分析所需要配置的分析仪器。阐述了空气分离分析系统的预处理     

Effects of the concentration-dependent density on liquid separation in a thermal-diffusion column

An analysis is given for the solution to a system of equations describing the separation in a liquid thermal-diffusion column. Similarity numbers are derived for the effects of concentration and thermal expansion on the separation. A method is given for calculating the thermal-diffusion constant that eliminates the effects of concentration on the density.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 12, No. 5, pp. 790–794, May, 1970.     

等离子体技术在膜分离领域的应用

综述低温等离子体技术在高分子分离膜研究过程中的应用与最新进展 ,结合超滤、渗透汽化、气体分离等具体膜过程的膜材料性能强化 ,指出等离子体技术作为分离膜材料表面改性的强有力手段 ,将会得到普遍重视和深入研究 .     

改造10000m~3/h空分上塔增产氧气

哈尔滨气化厂空分分厂1^#10000m^3／h空分设备是1991年杭州制氧机(集团)有限公司生产的，为全低压切换板翅式流程。1995年由于主冷微爆，对主冷进行过修复，并焊死部分通道。设计氧产量为10000m^3／h，纯度为98％O2。后因煤质变化和造气炉需要，氧纯度需提高到99.5％O2，生产能力     

Monolithic column HPLC separation of intact proteins analyzed by LC-MALDI using on-plate digestion: An approach to integrate protein separation and identification

A method is developed to integrate a protein separation by monolithic capillary reversed-phase high-performance liquid chromatography to on-probe tryptic digestion for subsequent analyses by MALDI-TOF MS and MALDI-TOF/TOF MS. The method provides a means of directly interfacing separations to MALDI-MS, reducing the amount of time required for traditional procedures involving in-solution enzymatic digestion and sample cleanup prior to MALDI-MS analysis. When used with pI-based fractionation as a first dimension, it provides a means of analyzing complex mixtures of proteins with minimal sample handling and cleanup. The use of monolithic capillary columns sufficiently resolved intact proteins so that peptide mass fingerprinting analysis by MALDI-TOF MS resulted in the identification of close to 40 unique proteins from 120 ng of sample obtained from a prefractionated MCF10 cell line at pH 6.34, where the identifications of several of these proteins were also confirmed by intact MW and tandem mass spectrometric analysis. The reproducibility of this method has been demonstrated to be sufficient for the purpose of protein identifications. Experimental values of protein intact MW are obtained and compared to that expected for each protein identified.     

精馏意识在空分系统操作中的运用

介绍精馏意识在空分系统操作中运用 ,举例说明了一种从全局角度考虑问题的方法 ,使操作更有预见性 ,保持精馏工况的稳定性。     

空分设备上塔进油分析及处理

介绍KDON-6000/18000型空分设备在进行裸冷及3#膨胀机试车过程中,大量润滑油(约200L)进入精馏塔系统,试车工作被迫中断。对上塔带油的原因和膨胀机漏油现象进行分析,提出处理措施及试车中应该注意的事项。