离子交换法从N-Ac-DL-Methionine的酶拆分液中分离制备L-Methionine和N-Ac-D-Methionine

依据N-Ac-DL-Methionine的酶拆分液及其组分特有的性质，采用强酸型阳离子交换柱成功地将拆分液中各组分进行分组．分析了流出液的pH和L-Met浓度的变化规律和原因；讨论并确定了柱的交换容量与所加拆分液中钠的含量的最佳比值范围．本实验方法不仅可以获得L-Met，且兼得N-Ac-D-Met，二者的收率在小试中分别达到85％以上75％左右．     

Some theoretical aspects of the use of isotopic exchange in a heterogeneous liquid system for radiochemical separations

Theoretical possibilities of the application of isotopic exchange in a heterogeneous liquid system to the separation of radionuclides have been investigated. With certain simplifying assumptions, equations were derived which enable the calculation of both the separation efficiency and volume concentration for a one-stage separation process under static or dynamic conditions. The relations obtained can be used in the choice of an appropriate method for the separation and simultaneous enrichment of trace amounts of radionuclides from large-volume liquid samples by equilibrium isotopic exchange.     

场放大进样-扫集胶束电动色谱法测定金银花中的咖啡酸与绿原酸

以场放大进样-扫集胶束电动色谱法( FASI - sweeping-MEKC)测定了金银花中的咖啡酸、绿原酸.考察了SDS浓度、进样电压、进水时间与进样时间比值、进样时间以及缓冲液组成对分离效果的影响.最佳分离条件为:采用未涂层熔融石英毛细管(50 cm × 50 μm,有效柱长33 cm),缓冲体系为100 mmol...     

The retention behaviour of amino acids in hydrophilic interaction liquid chromatography on zwitterionic stationary phases†

The retention behaviour of amino acids was studied in hydrophilic LC on zwitterionic stationary phases. Evaluation of the influences of acetonitrile/water content, ammonium acetate (NH₄Ac) concentration and mobile phase pH values was performed. Fourteen amino acids were tested and they were all retained to varying extents, with poorer retention in high water content eluents. The linear relationship between the logarithm of retention factor and log(water content) indicated that adsorption dominated or at least was partly involved in the separation mechanism. Electrostatic and hydrophilic interactions also contributed to the retention of these amino acids under different separation conditions with various mobile phase pH values and NH₄Ac concentrations. Thus, the overall retention mechanism could be explained as a combination of adsorption, electrostatic and hydrophilic interactions. The magnitude and contribution of each mechanism is dependent on the nature of the analyte and the separation conditions applied.     

Separation of acidic compounds by strong anion-exchange capillary electrochromatography

Separation of the acidic compounds in the ion-exchange capillary electrochromatography (IE-CEC) with strong anion-exchange packing as the stationary phase was studied. It was observed that the electroosmotic flow (EOF) in strong anion-exchange CEC moderately changed with increase of the eluent ionic strength and decrease of the eluent pH, but the acetonitrile concentration in the eluent had almost no effect on the EOF. The EOF in strong anion-exchange CEC with eluent of low pH value was much larger than that in RP-CEC with Spherisorb-ODS as the stationary phase. The retention of acidic compounds on the strong anion-exchange packing was relatively weak due to only partial ionization of them, and both chromatographic and electrophoretic processes contributed to separation. It was observed that the retention values of acidic compounds decreased with the increase of phosphate buffer and acetonitrile concentration in the eluent as well as the decrease of the applied voltage, and even the acidic compounds could elute before the void time. These factors also made an important contribution to the separation selectivity for tested acidic compounds, which could be separated rapidly with high column efficiency of more than 220000 plates/m under the optimized separation conditions.     

Multiobjective optimization of simulated moving bed and Varicol processes using a genetic algorithm

The size of the packing material, the total number of columns and the total feed concentration have significant impacts on the economics of a preparative chromatographic separation, through their effects on column pressure drop, column efficiency and thermodynamics. In this work, the role of these parameters on the performances of a simulated moving bed and a Varicol process is investigated on a chiral separation system from literature, using an equilibrium stage model. A multiple objective optimization technique based on a genetic algorithm is adopted, which allows to maximize simultaneously the purity of the extract and productivity of the unit. In this way, it is possible to optimize and compare the performances of both processes in a wide range of parameter values, so as to assess their relative potential under equally optimized conditions. The optimization results, i.e. the so-called Pareto sets, have been discussed in the frame of equilibrium theory and the roles of these three parameters have been clarified.     

Separation efficiency in protein zone electrophoresis performed in capillaries of different diameters

R-phycoerythrin (PHYCO, Mr 240 000), glucose-6-phosphate dehydrogenase (GPD, Mr 104 000) and two charge isomers of recombinant green fluorescent protein (GFP-1 and GFP-2, Mr 27 000) were subjected to capillary zone electrophoresis (CZE) in capillaries of 50, 100 and 150 microm inner diameter at various sample concentrations, electric field strengths, and lengths of the initial zone with the purpose of testing the hypothesis that protein - capillary wall interactions rather than thermal effects are predominantly responsible for the peak spreading of proteins in CZE. The efficiency of CZE was expressed in terms of the number of theoretical plates, N, or the plate height corrected by subtracting the contribution from initial zone length, H'. The latter has the advantage of solely reflecting contributions to the separation efficiency arising from intracolumn peak spreading in capillaries of different diameters. The separation efficiency measured varied widely, by two orders of magnitude, for these proteins under identical conditions, with GPD exhibiting the highest and PHYCO the lowest values of N. H' was found to be independent of sample concentrations within the concentration ranges studied, 1-100 microg/mL for PHYCO and 100-1000 microg/mL for GPD, while exhibiting a decrease with sample concentration for GFP, especially in 150 microm diameter capillaries, within the concentration range 1-100 microg/mL. H'was also found to be independent of electric field strength up to 300-400 V/cm for PHYCO and GFP. In all experiments, the CZE of proteins in 100 microm diameter capillaries provided a higher or, at least, equal efficiency, compared to that in 50 or 150 microm diameter capillaries. It may be concluded that the protein - capillary wall interactions and protein microheterogeneity are the dominant sources of peak spreading and their specific combinations are thought to be responsible for the wide variation in separation efficiency between proteins in CZE observed under identical conditions.     

Factors influencing performance in the rapid separation of aflatoxins by micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MECC) is applied to the high-speed analysis of aflatoxins. Baseline separation of the four common aflatoxins G(1), G(2), B(1) and B(2), is accomplished in less than 30 sec. Small (25 mum) internal diameter capillaries are found to be critical in maintaining high efficiency under rapid MECC separation conditions. Van Deemter-like plots are generated in order to study the effects of capillary diameter and organic solvent on efficiency under high electric field conditions. Other experimental parameters affecting efficiency are investigated, including buffer concentration, surfactant concentration, and detector time constant. Simple on-column laser-based fluorescence detection, employing helium-cadmium laser radiation at 325 nm for excitation, allows for limits of detection in the range of 0.05-0.9 femtomoles injected for underivatized aflatoxins. Considerations important in the analysis of aflatoxins in real matrices are presented.     

Selectivity differences of water‐soluble vitamins separated on hydrophilic interaction stationary phases

In this study, the retention behavior and selectivity differences of water‐soluble vitamins were evaluated with three types of polar stationary phases (i.e. an underivatized silica phase, an amide phase, and an amino phase) operated in the hydrophilic interaction chromatographic mode with ESI mass spectrometric detection. The effects of mobile phase composition, including buffer pH and concentration, on the retention and selectivity of the vitamins were investigated. In all stationary phases, the neutral or weakly charged vitamins exhibited very weak retention under each of the pH conditions, while the acidic and more basic vitamins showed diverse retention behaviors. With the underivatized silica phase, increasing the salt concentration of the mobile phase resulted in enhanced retention of the acidic vitamins, but decreased retention of the basic vitamins. These observations thus signify the involvement of secondary mechanisms, such as electrostatic interaction in the retention of these analytes. Under optimized conditions, a baseline separation of all vitamins was achieved with excellent peak efficiency. In addition, the effects of water content in the sample on retention and peak efficiency were examined, with sample stacking effects observed when the injected sample contained a high amount of water.     

Impact of a pressure drop on a monolithic capillary column on the efficiency and separation ability of the column

The impact of inlet and outlet column pressures on column separation properties was investigated for monolithic capillary column in gas chromatography. It was demonstrated that the classical Van Deemter equation does not allow us to make a clear choice of the optimal separation conditions. More relevant data can be obtained from the dependence of the height equivalent to a theoretical plate (HETP) on the inlet and outlet column pressures. The dependence ensures that the minimum HETP value can be achieved at high values of inlet and outlet column pressures, but the ratio of the pressures must approach 1. The efficiency of the column under these optimal conditions can exceed by 25–35% the column efficiency under the optimal conditions found using the classical Van Deemter plot. It was shown that a decrease in inlet and outlet column pressures even at a relative pressure close to 1 leads to an increase in HETP and the loss of column separation ability.     

Band broadening caused by the multiple labeling of proteins in micellar electrokinetic chromatography with diode laser-induced fluorescence detection

When a labeling reagent is used, in the determination of proteins by capillary electrophoresis with laser-induced fluorescence detection, the multiple labeling of proteins frequently occurs, which can degrade the separation efficiency. In order to understand the influence of the multiple labeling of proteins on separation efficiency, the band broadening caused by a labeling reaction between bovine serum albumin (BSA) and a cyanine fluorescent dye (Cy5) was investigated using micellar electrokinetic chromatography in conjunction with diode laser-induced fluorometry. With the aid of an internal standard, methylene blue, the height equivalent to the theoretical plate (HETP) ratio of BSA to methylene blue was used as an indicator for band broadening under optimum separation conditions. Labeling conditions, including reaction buffer pH, reaction time, and initial concentration of Cy5 to bovine serum albumin, were found to influence the HETP ratio. The separation efficiency for the labeled protein was degraded by experimental conditions employed in the labeling, which indicates an increase in the heterogeneity of the final products.     

一种简单的制备反相电色谱柱的方法

 采用简便易行的方法自制内径为100 μm的电色谱柱,并考察了其性能,同时研究了磷酸盐缓冲液浓度、乙腈体积分数、电压、柱温对中性化合物保留行为的影响。     

高速离子交换色谱法分离重金属离子及铜和锌的测定

本文使用国产SY-202高速离子交换色谱仪(库仑检测器)以及国产YSG-SO₃Na型阳离子交换树脂研究了铜、锌、镍、钴、镉、铅和锰等七种二价离子在酒石酸盐、乳酸盐及柠檬酸盐体系洗脱液中的分离情况,考察了洗脱液及其流速对保留时间和柱效的影响以及不同离子和不同进样量对电解效率的影响。测定了黄铜和废水样品中的铜和锌。     

Separation of131I by isotopic and non-isotopic liquid ion exchange

A study is presented on the use of isotopic and non-isotopic ion exchange in a heterogeneous liquid-liquid system for the separation of¹³¹I from water. The method is based on the reaction between radioiodide in the aqueous phase and trioctylmethylammonium iodide or chloride in the organic phase. The effect of some important experimental parameters on the separation efficiency is discussed. It has been found that under optimum conditions the method of isotopic ion exchange can be used for the radiochemical determination of iodine in water.     

Preconcentration neutron activation analysis of lanthanides by cloud point extraction using PAN

Summary Methods for the simultaneous preconcentration of lanthanides by cloud point extraction and their determination using neutron activation analysis have been developed. The preconcentration method involves the use of a nonionic surfactant and a chelating agent. A fairly small volume of surfactant-rich phase was obtained under optimized experimental conditions, leading to detection limits between 0.3 and 3.0 ng ^. g^-1. Critical parameters that influence extraction efficiency were solution pH and concentration of chelating agent, and to a lesser extent, ionic strength and temperature. Most of the chelates were quantitatively extracted (>90%) at high pH values. Selective separation can be achieved by varying some of the experimental conditions.     

Experimental design optimization of the capillary electrophoresis separation of leucine enkephalin and its immune complex

To optimize the capillary electrophoretic separation conditions for leucine enkephalin (LE) and the immune complex of the LE and anti-LE reaction, an analysis using a three-level, three-factorial Box-Behnken design was performed. Three separation parameters, buffer pH (X(1)), buffer concentration (X(2)), and applied voltage (X(3)), were chosen to observe the effect on separation responses. The responses were theoretical plate number, migration time of the LE peak, and resolution between the peaks. The optimum conditions and process validation were determined using statistical regression analysis and surface plot diagrams. The capillary electrophoresis optimum separation conditions were established to be 75 mM phosphate buffer at pH 7.00 with an applied separation voltage of 15 kV. By using the analysis technique, the prediction of responses was satisfactory and process verification yielded values within the +/-5% range of the predicted efficiency.     

青枯雷尔氏菌特征菌株高效离子交换色谱快速分离条件的优化

建立了高效离子交换色谱和紫外检测系统快速分离青枯雷尔氏菌的细菌色谱方法。通过比较青枯雷尔氏菌悬浮在哌嗪-HCl缓冲体系和双蒸水后的菌体数变化及细胞形态变化,分析该缓冲液对青枯雷尔氏菌生长活性及细胞表面特性的影响。结果表明,青枯雷尔氏菌悬浮在平衡缓冲液、洗脱缓冲液和双蒸水中的菌体数量无明显差异,分别为6.467×10⁹、6.267×10⁹和6.233×10⁹ cfu/mL。透射电镜观察发现,3种溶液处理后,青枯雷尔氏菌均保持完整的细胞结构。研究了缓冲液pH值、流速及菌体细胞浓度对青枯雷尔氏菌色谱分离效果的影响,确定青枯雷尔氏菌的最佳色谱分离条件为：缓冲液pH值为8.0,流速为2 mL/min,菌体浓度大于1.0×10⁸ cfu/mL且小于1.0×10¹⁰ cfu/mL。该分离条件缩短了分离时间,提高了分离效率,为快速分离青枯雷尔氏菌提供了一种有效的手段,同时也为细菌等微生物的分离提供了新途径。     

Electrochemical Behavior of Cu Electrode and Its Application in CE Determination of Polyols

The electrochemical behavior of a copper (Cu) electrode and its application in capillary electrophoresis determination of polyols was investigated in order to understand the redox property of Cu and achieve better separation efficiency. Electrochemical measurements were performed using a Cu electrode (fresh or oxidized) in buffer solutions having different pH values (7.8–13.0) by cyclic voltammetry. The Cu electrode showed higher electroactivity under stronger alkaline conditions. Further, the Cu electrode was found suitable for detecting weak oxidizing or reducing polyhydroxy compounds because of the redox reactions among Cu, Cu(I), and Cu(II) species. Thus, the Cu electrode was used in capillary zone electrophoresis (CZE) for separation and determination of propanediol and glycerol, weak electroactive polyols, using different separation (pH 8.7) and detection (pH 11.04) buffers. Separation and detection buffers with different pH values in CZE technology could offer efficient separation efficiency and detection limits at the same time.     

Characterization of enhanced-fluidity liquid hydrophilic interaction chromatography for the separation of nucleosides and nucleotides

Hydrophilic interaction chromatography (HILIC) is a liquid chromatographic separation mechanism commonly used for polar biological molecules. The use of enhanced-fluidity liquid chromatography (EFLC) with mixtures of methanol/water/carbon dioxide is compared to acetonitrile/water mobile phases for the separation of nucleosides and nucleotides under HILIC conditions. Enhanced-fluidity liquid chromatography involves using common mobile phases with the addition of substantial proportions of a dissolved gas which provides greater mobile phase diffusivity and lower viscosity. The impact of varying several experimental parameters, including temperature, addition of base, salt, and CO₂ was studied to provide optimized HILIC separations. Each of these parameters plays a key role in the retention of the analytes, which demonstrates the complexity of the retention mechanism in HILIC. The tailing of phosphorylated compounds was overcome with the use of phosphate salts and the addition of a strong base; efficiency and peak asymmetry were compared with the addition of either triethylamine (TEA), 1,4-diazabicyclo [2.2.2] octane (DABCO) or 1,5-diazabicyclo [4.3.0] non-5-ene (DBN). DBN and DABCO both led to increased efficiency and lower peak asymmetry; DBN provided the best results. Sodium chloride and carbon dioxide were added to enhance the selectivity between the analytes, giving a successful isocratic separation of nucleosides and nucleotides within 8 min. The retention mechanism involved in EFL-HILIC was explored by varying the temperature and the mole fraction of CO₂. These studies showed that partitioning was the dominant mechanism. The thermodynamics study confirmed that the solvent strength is maintained in EFLC and that a change in entropy was mainly responsible for the improved selectivity. The selectivity using methanol/water/carbon dioxide varied greatly compared to that obtained with acetonitrile/water. Finally while this study highlights the optimization of EFL-HILIC for the separation of nucleosides and nucleotides under isocratic conditions, this is also an example of the broad range of polarities of compounds that EFL-HILIC can separate.     

Stepwise capillary electrophoretic separation of DNA fragments using poly(ethylene oxide) solutions in the presence of electroosmotic flow.

Single-base resolution in the separation of DNA markers V and VI was achieved in the presence of electroosmotic flow (EOF), using poly(ethylene oxide) (PEO) solutions containing ethidium bromide (EtB) under isocratic conditions. Furthermore, a new approach called stepwise capillary electrophoresis (SCE) has been developed for DNA analysis, including stepwise changes in PEO concentration, EtB concentration as well as both PEO and EtB concentrations, wherein the EOF was used to introduce different PEO solutions into the capillary during the separation. DNA fragments smaller than 80 bp were both detected under isocratic conditions using 20 micrograms/ml EtB, and SCE using 1 and 20 micrograms/ml EtB, but not under isocratic conditions using 1 microgram/ml EtB. Resolution and speed of the DNA separation in SCE were different from those obtained from isocratic means, indicating that DNA underwent different concentrations of PEO and EtB in SCE. For example, DNA fragments with 458 and 504 base pairs (bp) were partially resolved in SCE, but not under isocratic conditions. The results further suggest that it is worth developing gradient techniques for widening the separation range and enhancing resolution in DNA analysis.