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1.
Summary In electrochromatography, electrolyte is driven along a narrow bore chromatographic column at typical HPLC linear velocities by applying a potential gradient of around 50,000 V m−1. Contrasting with pressure driven LC, the tube bore is limited to not more than 200 μm by self heating. Thus miniaturisation is mandatory in electrochromatography whereas it is optional in pressure driven LC unless very small particles (e.g. 1 μm diameter) are used. Because the velocity profile in open tubular electrochromatography is close to that of perfect plug flow, contrasting with the parabolic flow profile in pressure driven LC, open tube electrochromatography provides plate efficiencies limited only by axial diffusion, and comparable to those obtainable in open tubular gas chromatography. Contrasting with pressure driven open tubular LC there is no requirement for the tube bore to be very small (e.g. <10 μm). Although pure electrophoresis is applicable only to ionised solutes, and is not strictly a chromatographic method, neutral species can be chromatographed by partitioning them between two phases which move at different rates, for example by using micellar solutions or colloidal sols as the moving fluid, thereby retaining the high plate efficiency of electrophoresis. With packed tubes electrochromatographic separations of high efficiency can be obtained with 5 μm particles and extremely high efficiencies should be obtainable without sacrifice of eluent velocity by using submicron particles. In principle, electrochromatographic methods can provide a wide range of partitioning methods of extremely high plate efficiency, and will, in future, undoubtedly rival conventional HPLC.  相似文献   

2.
Cai Y  Janasek D  West J  Franzke J  Manz A 《Lab on a chip》2008,8(11):1784-1786
Shear stress has been exploited within a channel-free rotating plate system for the circular chromatographic separation of model analytes.  相似文献   

3.
The retention characteristics of some adamantane derivatives under conditions of normal-phase and reversed-phase high-performance liquid chromatography were examined. The values of the retention factor and relative retention factor for chromatographing with various eluents were obtained. The effects of the nature and elution strength of the mobile phase on the retention characteristic of adamantane derivatives were studied.  相似文献   

4.
Silica microspheres have been synthesized by phase separation and sol–gel transition coupled with emulsion method. The as-obtained material is characterized by scanning electron microscopy, nitrogen sorption, elemental analysis and particle size distribution measurements. The results demonstrated that the material featured with hierarchically porous structure, possessing both mesopores and penetrable macropores. The mesopores provide large surface area while the macropores traverse the silica particles, which may facilitate fast mass transfer as well as guarantee low backpressure when such materials are used for packed high-performance liquid chromatography (HPLC) column. Therefore, their preliminary applications as HPLC packings in fast separation and low-pressure separation have been attempted in the present study. Benzene, benzaldehyde and benzyl alcohol were separated within two minutes on the silica column at a flow rate of 7 mL min−1. Vitamin E mixtures can also be baseline separated at a high flow rate of 8 mL min−1. In addition, thirteen aromatic hydrocarbons were well separated on the octadecyl-bonded silica (ODS) column. In comparison with a commercial Kromasil ODS column, the pressure of the proposed column is much lower (<1/2) under the same chromatographic conditions, while comparable separation efficiency can be achieved.  相似文献   

5.
Summary A sensitive capillary gas chromatographic method is described for the simultaneous determination of lidocaine, tetracaine, procaine and dibucaine. The method was applied to the determination of anesthetics in tissue homogenates incubated at 38°C at doses between 10 and 400 mg/kg. In the liver tissue thein vitro metabolization of the studied anesthetics is most rapid for tetracaine, also fast for procaine, while for lidocaine and dibucaine the metabolization is very slow. In brain tissue thein vitro metabolization of anesthetics is very slow.The method shows good analytical parameters: linearity between 5 and 40 g/ml; day-to-day reproducibility ca. 8% for a concentration of 20 g/ml, precision ca. 7% for a concentration of 20g/ml. Accuracy is also very good.  相似文献   

6.
Important parameters to consider when developing a liquid chromatography/mass spectrometry (LC/MS) method are buffer type and concentration, and column geometry. In the work presented here the choice of buffer for the analysis of basic compounds using a polar embedded phase (HyPURITYtrade mark ADVANCE) is illustrated for the analysis of tricyclic antidepressants. Method transfer from a 4.6 mm i.d. column to a 2.1 mm i.d. column is demonstrated for the analysis of triazines and anabolic steroids and their metabolites, with no change in selectivity and with added speed of analysis. Analysis of eight beta-blockers is achieved in 65 seconds by using a short 30 x 4.6 mm C18 column.  相似文献   

7.
All the experimental parameters that the chromatographers are used to consider as constant (the column length and its diameter, the particle size, the column porosities, the phase ratio, the column hold-up volume, the pressure gradient along the column, the mobile phase density and its viscosity, the diffusion coefficients, the equilibrium constants, the retention factors, the efficiency parameters) depend on pressure to some extent. While this dependence is negligible as long as experiments, measurements, and separations are carried out under conventional pressures not exceeding a few tens of megapascal, it is no longer so when the inlet pressure becomes much larger and exceeds 100 MPa. Equations are developed to determine the extent of the influence of pressure on all these parameters and to account for it. The results obtained are illustrated with graphics. The essential results are that (1) many parameters depend on the inlet pressure, hence on the flow rate; (2) the apparent reproducibility of parameters as simple as the retention factor will be poor if measurements are carried out at different flow rates, unless due corrections are applied to the results; (3) the influence of the temperature on the equilibrium constants should be studied under constant inlet pressure rather than at a constant flow rate, to minimize the coupling effect of pressure and temperature through the temperature dependence of the viscosity; and (4) while reproducibility of results obtained at constant pressure and flow rate will not be affected, method development becomes far more complex because of the pressure dependence of everything.  相似文献   

8.
In this study, ultra performance liquid chromatography (UPLC) using pressures up to 1,000 bar and columns packed with sub-2 microm particles has been combined with high temperature mobile phase conditions (up to 90 degrees C). By using high temperature ultra performance liquid chromatography (HT-UPLC), it is possible to drastically decrease the analysis time without loss in efficiency. The stability and chromatographic behavior of sub-2 microm particles were evaluated at high temperature and high pressure. The chromatographic support remained stable after 500 injections (equivalent to 7,500 column volumes) and plate height curves demonstrated the capability of HT-UPLC to obtain fast separations. For example, a separation of nine doping agents was performed in less than 1 min with sub-2 microm particles at 90 degrees C. Furthermore, a shorter column (30 mm length) was used and allowed a separation of eight pharmaceutical compounds in only 40s.  相似文献   

9.
Summary The normal-phase chromatographic retention behaviour of polyesters on bare silica and on a polymer-based polyamine (PA) column has been studied with a variely of binary mobile phases under isocratic conditions. The dependence of experimental retention data on the degree of polymerization (p) and on mobile phase composition (φ) was characterized by to an approach developed by Jandera et al. The bulky repeating unit and the relatively highly polar end groups of the polyesters both had a large influence on retention behaviour. The two effects in combination explain the molar-mass-independent retention observed experimentally at a particular mobile phase composition for all the mobile phase—stationary phase combinations investigated. These conditions were found to be independent of the type of end group. End group separation on a silica column improves when the polarity of the less polar solvent is increased. End group separation is better on the PA column because of a greater difference between the adsorption energy of the alcohol and acid end groups. Better prediction of retention data on the PA column was achieved by use of an approach which assumes two different types of adsorption site. Results enabled further understanding of retention behaviour in normalphase gradient polymer-elution chromatography (NPGPEC) and explained both the dependence of the order of elution onp and differences between the end-group selectivity of different systems.  相似文献   

10.
The preparation of stationary phases for HPLC using polymers deposited on silica usually includes an immobilization step involving cross-linking by free radicals induced by ionizing radiation or by other radical initiators. The present paper reports changes which occur at ambient temperature in the character of poly(methyloctylsiloxane) deposited on porous silica particles as a function of the time interval between particle loading and column packing. Column performance and retention factors increase with time and these changes are attributed to rearrangement (self-assembly) which result in "self-immobilization" of the polymer molecules on the silica surface.  相似文献   

11.
Pressure driven liquid chromatography (LC) is a powerful and versatile separation technique particularly suitable for differentiating species present in extremely small quantities. This paper briefly reviews main historical trends and focuses on more recently developed technological approaches in miniaturization and on-chip integration of LC columns. The review emphasizes enabling technologies as well as main technological challenges specific to pressure driven separations and highlights emerging concepts that could ultimately overcome fundamental limitations of conventional LC columns.  相似文献   

12.
Hydrophilic interaction chromatography has been applied for the separation of epirubicin and its analogues using high-purity silica column with aqueous-organic mobile phase. Parameters affecting the chromatographic behavior of the solutes such as organic modifier, buffer pH, ionic strength and sample size, have been investigated. Of utmost importance for successful separation of these analogues is the choice of organic modifier, since it impacts both the solvent selectivity and the ionization of silica silanols as well as buffer solution, and consequently the retention behavior of solutes. Acetonitrile was shown to offer superior separation of these analogues to methanol, isopropanol or tetrahydrofuran. Results of the effects of organic modifier, buffer pH and ion strength indicate that the retention mechanism is a mixed-mode of adsorption and ion exchange. In addition, an irreversible adsorption of these compounds was found on silica in the weakly acidic or neutral mobile phases, and the effect of various factors on irreversible adsorption was also preliminarily discussed. More significantly, these basic compounds have exhibited peaks with a slanted front and a sharp tail, a typical overloading peak profile belonging to the behavior of competitive anti-Langmuir isotherm by increasing the sample size at the experimental conditions.  相似文献   

13.
Two different strategies for coupling liquid chromatography with atmospheric pressure matrix assisted laser desorption/ionization (AP MALDI) are presented. The first method is flow-injection liquid AP UV-MALDI. Compared with previous similar research, the detection limit was improved 10 times to 8.3 fmol using a solution of 50 nM peptide with 25 mM α-cyano-4-hydroxycinnamic acid. The applicability of this method to measure oligosaccharides, actinomycin antibiotics, antibiotics, phosphopeptides, and proteins is demonstrated. The upper mass limit achieved with the current instrumentation is 6,500 Da (doubly charged cytochrome c). The feasibility of a second strategy based on single-droplet IR AP MALDI is demonstrated here. Aqueous peptide solutions were successfully measured by this method.  相似文献   

14.
This paper describes the assembly, usage, operation, and separation results of a medium pressure liquid chromatography (MPLC) instrument. Its ability to separate compounds with high resolution makes it a powerful tool for many chemistry laboratories. This equipment can be easily built from inexpensive commercially available materials. Due to the constant reuse of packing materials and infrequent maintenance, MPLC provides a simple, reliable, and economical means of purification.  相似文献   

15.
The chromatographic performance of the deuterated solvents, CD3OD and D2O, has been investigated in reversed-phase micro high performance liquid chromatography. The chromatographic performance of CD3OD is only slightly superior to that of CH3OH. However, the performance of D2 is significantly superior to that of H2O, separation of aromatics being improved by about 30%. D2 is a particularly powerful solvent for the separation iof deuterated and non-deuterated compounds.  相似文献   

16.
Fast liquid chromatographic (LC) methods are important for a variety of applications. Reducing the particle diameter (d(p)) is the most effective way to achieve fast separations while preserving high efficiency. Since the pressure drop along a packed column is inversely proportional to the square of the particle size, when columns packed with small particles (<2 microm) are used, ultrahigh pressures (>689 bar) must be applied to overcome the resistance to mobile phase flow. Elevating the column temperature can significantly reduce the mobile phase viscosity, allowing operation at higher flow rate for the same pressure. It also leads to a decrease in retention factor. The advantage of using elevated temperatures in LC is the ability to significantly shorten separation time with minimal loss in column efficiency. Therefore, combining elevated temperature with ultrahigh pressure facilitates fast and efficient separations. In this study, C6-modified 1.0 microm nonporous silica particles were used to demonstrate fast separations using a temperature of 80 degrees C and a pressure of 2413 bar. Selected separations were completed in 30 s with efficiencies as high as 220,000 plates m(-1).  相似文献   

17.
The chromatographic behavior of native titania was investigated in aqueous normal phase chromatography using a set of N-methylated xanthines as polar test solutes. In agreement with a hydrophilic interaction on a polar bed, the retention of xanthine models increased mainly along their molecular polarity. Adsorption of these molecules on the hydrated surface of titania prevailed as a retention mechanism for low water contents in the mobile phase. Several N-methylated xanthines could be easily discriminated along the number and position of their methyl groups while the nitrogen atom at position 3 was found deeply involved in the retention on titania. To get further insights on the interactions occurring on the surface of titania, the retention of xanthine derivatives based on ligand-exchange was evaluated as a function of the buffer concentration and type. The separation efficiency of native titania for the set of N-methylated xanthines was comparable to that observed on zirconia but lower than that obtained on native silica due to mixed-mode interactions. However, titania exhibited a superior ability to recognize several isomeric positions of xanthine derivatives in comparison to zirconia and silica.  相似文献   

18.
Macroporous cellulose beads (MCB) used as anion exchangers were successfully prepared from cellulose solution in ionic liquid by double emulsification followed by cross-linking and modification with diethylaminoethyl. The pore structure and properties of the MCB were investigated and the results were compared with homogeneous cellulose beads (HCB). The MCB in size of about 71 μm is characterized by two sets of pores, i.e., diffusion pores (10–20 nm) and macropores (800–2000 nm), determined by mercury porosimeter. In addition, the bed permeability and effective porosity for BSA of MCB-packed column are 58% and 25% higher than those of HCB-packed column, respectively. The adsorption properties of MCB were evaluated, and compared with HCB and commercial absorbent (Sepharose 6 Fast Flow, CSFF). It is found that the pore diffusivity of BSA in MCB is over 7.9 times higher than HCB, and 6.7 times higher than CSFF, respectively. While the equilibrium adsorption capacity (qm) of BSA on MCB is obviously lower than that on HCB and CSFF, the dynamic binding capacity (DBC) on MCB at 10% breakthrough reaches 47.7 mg/mL, higher than HCB (40.3 mg/mL) and CSFF (46.2 mg/mL) at flow rate of 360 cm/h. In addition, the MCB-packed column showed better column efficiency over the HCB packed one. Therefore, we demonstrated that the MCB possessed more advantages than other ones, like HCB and CSFF, and was expected as an ideal material for fast chromatography.  相似文献   

19.
20.
The present work aims at the optimisation of the synthesis of methyl-silsesquioxane monolithic capillary columns using a sol-gel based protocol. The influence of reaction conditions such as temperature, reaction mixture composition and catalyst concentration has been examined. The morphology of the products was studied by scanning electron microscopy and nitrogen adsorption. Monolithic capillary columns were obtained with a skeleton-like structure with open pores. Pore diameters vary from 0.8 to 15 microm, diameters of the xerogel network vary from 0.4 to 12 microm, respectively. Specific surface areas up to 334 m2/g have been observed, however, many materials did not possess areas above few m2/g which represents the limit of detection of the nitrogen porosimetry measurements. Excellent adhesion to the capillary wall was observed in all cases, and drying was possible at ambient conditions without the formation of cracks.  相似文献   

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