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1.
This paper presents an extension of a previous investigation in which the behavior of nonpolar compounds in temperature-programmed
gas chromatographic runs was predicted using thermodynamic (entropy and enthalpy) parameters derived from isothermal runs.
In a similar manner, entropy and enthalpy parameters were determined for a Grob standard mixture of compounds with widely
varying chemical characteristics. These parameters were used to predict the retention times and chromatographic behaviors
of the compounds on four gas chromatography capillary columns: three that had phenyl-based stationary phases (with degrees
of substitution of 0%, 5% and 50%) and one with (50%) cyanopropyl substitution. The predictions matched data empirically obtained
from temperature-programmed chromatographic runs for all of the compounds extremely well, despite the wide variations in polarity
of both the compounds and stationary phases. Thus, the results indicate that such simulations could greatly reduce the time
and material costs of chromatographic optimizations. 相似文献
2.
The efficiency of capillary columns in programmed temperature analysis can be evaluated by calculation of the separation number (“Trennzahl”). A procedure for the prediction of this parameter at various initial temperatures, carrier gas pressures and heating rates, by using as the starting data the retention times and the peak widths obtained in some isobaric and isothermal runs is described. An equation is proposed that permits to obtain the values of the peak width at half height in any isothermal and linearly programmed temperature gas chromatographic run and therefore to calculate the separation number value. The effect on this parameter of the column polarity was investigated by using polar and non-polar compounds (n-alkanes and 1-alcohols). 相似文献
3.
A method for the prediction of the retention time and the resolution of chromatographic peaks in different experimental conditions by starting from few experimental data measured in isothermal and isobaric analyses was published previously. In this paper, the same mathematical model was implemented for calculating the retention times and the column efficiency in programmed pressure runs. Some models originated from the Golay equation and reported in the literature are compared, and a new modified equation for the calculation of the peak width at half height is proposed. The procedure for the prediction of the retention time and the peak width at half height at programmed pressure of the carrier gas and different column temperature and linear gradient by using retention data of different compounds obtained in few isobaric runs is described. The prediction of the retention time and the separation efficiency of compounds with different polarity gave good results for the programmed pressure runs with linear gradient. The effect of the variation of the initial parameters of the experimental analyses and of the mathematical model on the accuracy of the prediction has been evaluated. 相似文献
4.
The conventional analytical HPLC was successfully developed for micro‐column separation by using a simple eluate splitting system, self‐preparation of packing column and on‐capillary column detector in our laboratory. Porous inlet frit in fused silica capillary was rapidly prepared by sintering stainless steel powders under 500 meshes for about 20 s. The use of such frits or metal meshes in capillary to retain C18 particles of chromatographic packing was demonstrated to be stable and specially robust with continuous packing and long chromatographic runs. Furthermore, the chromatographic behavior was detailedly evaluated by changing the flow rate and the percentage of mobile phase using the prepared capillary column. Under the optimal experimental conditions, baseline separation of the model analytes including thiourea, benzene, toluene, ethylbenzene was obtained with a high column efficiency near 70000N (plates/m) by the developed capillary‐HPLC. 相似文献
5.
Programming inlet pressure in gas chromatography permits to decrease the analysis time without changing the elution order of compounds of different polarity whose relative retention changes with changing temperature. The choice of the best values of the inlet pressure and flow-rate of the carrier gas often requires many preliminary analyses with different parameters to be carried out. A method for the prediction of the separation by starting from few experimental data measured in isothermal and isobaric conditions decreases the time required for the optimisation of the analysis. The efficiency of the separation depends on the change of the theoretical plate height at various pressures and temperatures, due to pressure drop along the column. By calculation of the diffusion coefficients of the analysed compounds into the mobile and stationary phase it is possible to evaluate the column efficiency and predict the number of theoretical plates at any inlet pressure. A procedure for the prediction of the plate height of a capillary column at any inlet pressure of the carrier gas and column temperature by using retention data of polar and non-polar compounds (1-alcohols and linear alkanes) obtained in few isobaric runs is described. 相似文献
6.
A fused silica capillary column was packed with RP(18) silica stationary phase entrapping the particles between two frits obtained by two different procedures. The inlet frit consisted of a short organic polymer made via a thermopolymerization process while the outlet frit was prepared by sintering the octadecylsilica (ODS) material. The packed column was employed in capillary electrochromatography (CEC) experiments for the separation of three selected test compounds. Retention time and separation efficiency were evaluated. Results were compared with those ones obtained with a packed capillary containing the same stationary phase entrapped between two sinterized frits. The novel packed column exhibited comparable separation efficiency and resolution with the traditional one. However, it allowed experiments without pressure support during the runs with no bubble formation. 相似文献
7.
The effective plate height, heff, is considered to be a better measure of the efficiency of capillary column than the conventional plate height, h, in isothermal conditions. By using experimental data of 1-alcohols and n-alkanes, 2-ketones and 1-alkenes measured on capillary columns coated with non-polar stationary phases in isothermal and isobaric conditions, the peak width at half height is predicted with a function similar at that of adjusted retention time. The results obtained under different analytical conditions as the head pressure and the temperature of the column confirm the validity of the model, whose parameters are linear, and as a consequence a unique solution is obtained. 相似文献
8.
Summary Retention data have been measured for model substances of different polarities under isothermal conditions at several temperatures using capillary columns coated with Carbowax-20M and SP-2100 stationary phases. By using the k capacity ratios obtained for various temperatures the thermodynamic characteristics of the partition process were determined. For homologous series linear relationships can be established between thermodynamic characteristics and carbon number. Thermodynamic characteristics can be used both to compare and evaluate column quality and to predict retention indices for different temperatures and linear programmed temperature conditions.Dedicated to Professor J. F. K. Huber on the occasion of his 60th birthday. 相似文献
9.
A method for the preparation of a silica monolithic capillary electrochromatography (CEC) column for the separation of enantiomers has been developed. The porous silica monolith was fabricated inside a fused-silica capillary column by using the sol-gel process. After gelation for 24 h, hydrothermal treatment at 100 degrees C for 24 h was performed to prevent the sol-gel matrix from cracking. The prepared monolith was then coated with Chirasil-beta-Dex which represents a chiral polymer prepared by grafting permethyl-beta-cyclodextrin to polymethylsiloxane with an octamethylene spacer. Immobilization of Chirasil-beta-Dex was performed by heat treatment at 120 degrees C for 48 h to give a nonextractable coating. The column performance was evaluated by using racemic hexobarbital as a model compound. The efficiency of 9.2 x 10(4) theoretical plates/m for the first eluted enantiomer of hexobarbital was obtained at an optimal flow rate of the mobile phase. The effect of mobile phase composition on enantiomeric separation of hexobarbital was also investigated. The column proved to be stable for more than one hundreds of runs during a two-months period. The enantiomers of several neutral and negatively charged chiral compounds were baseline separated on this column. 相似文献
10.
Analysis of parsley and fennel essential oils was performed by using low-pressure gas chromatography-mass spectrometry (GC-MS). The low-pressure instrument configuration was achieved by fitting a GC-MS instrument with a 530microm I.D. capillary column and an appropriate capillary restrictor at the inlet of the column. Comparison of the performance of the low-pressure GC-MS setup was made with fast GC-MS using a narrow-bore capillary column. By comparing the two approaches side-by-side the benefits of low-pressure GC-MS for characterisation of moderately complex essential oils comprising less than 50 detectable components can be fully appreciated. Although efficiency is sacrificed, the improved sample capacity of the 530microm I.D. column leads to higher peak intensities and in-turn better mass spectral library matching thus providing highly satisfactory results. 相似文献
11.
The gas chromatographic behavior of selected linear and non-linear alcohols and amines was investigated using four capillary
columns containing phenyl substitution levels of 0%, 5%, and 50% and 50% cyanopropyl substitution. In a previous study, the
positions of specific compounds inside the capillary column were iteratively modeled using only two thermodynamic parameters
(ΔH and ΔS). The present study addresses the validation of the two-parameter model for retention time prediction for selected alcohols
and amines using thermodynamic data obtained from as few as two data points. The difference between predicted and observed
retention times under different temperature conditions was generally less than 1% of the experimental value and the predicted
order of elution was correct in the used model. 相似文献
12.
A novel open-tubular capillary electrochromatography (OT-CEC) column coated with 2,6-dibutyl-beta-cyclodextrin (DB-beta-CD) was prepared using sol-gel technique. In the sol-gel approach, owing to the three-dimensional network of sol-gel and the strong chemical bond between the stationary phase and the surface of capillary columns, good chromatographic characteristics and unique selectivity in separating isomers were shown. We achieved high efficiencies of 5-14 x 10(4) plates/m for the isomeric nitrophenols using the sol-gel-derived DB-beta-CD columns. The migration time reproducibility of the separation of the isomeric nitrophenols was better than 2.2% over five runs and 4.5% from column to column. These sol-gel-coated DB-beta-CD columns have shown improved separations of isomeric aminophenols, isomeric dihydroxybenzenes and isomeric nitrophenols, in comparison with the sol-gel matrix capillary column. The influences of buffer pH and methanol solvent on separation were investigated. The chiral resolution of enantiomers such as ibuprofen and binaphthol was explored primarily. 相似文献
13.
Effects of concentration gradient on double-stranded DNA (dsDNA) separation by capillary electrophoresis are presented. By using a concentration gradient in the range between 0.8% and 3.2% for poly(N,N-dimethylacrylamide) (PDMA), the presence of a mesh-size gradient in the capillary could enhance the separation of larger size DNA fragments, better than that based on a single uniform concentration over the same capillary length. A decrease in the column length could make the gradient effect more obvious. An optimal capillary length could be achieved by using a judicious combination of the concentration gradient and the concentration range, yielding a maximum resolution for the system. The standard deviation of the migration time measured for each DNA fragment was less than 5% in ten continuous runs, suggesting that the gradient formed inside the column was quite stable. 相似文献
14.
New peak broadening parameter for the characterization of separation capability in capillary electrophoresis
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The influence of separation conditions on peak broadening is usually estimated by the number of theoretical plates. Using the data available in literature and experimental data, it is shown that in pressure‐assisted capillary electrophoresis the plate number is not directly related to the separation capability of conditions used. The experiments at different electrolyte flow velocities demonstrate that a higher plate number (the best separation efficiency) can be obtained with a lower peak resolution. Since ions are separated by electrophoresis due to the difference in electrophoretic mobilities, the peak width in terms of electrophoretic mobility is suggested as a new peak broadening parameter describing the separation capability of the conditions used. The parameter can be calculated using the tailing factor and the temporal peak width at 5% of the peak height. A simple equation for the resolution calculation is derived using the parameter. The advantage of the peak width in terms of mobility over other parameters is shown. The new parameter is recommended to be used not only in pressure‐assisted capillary electrophoresis but also in general capillary electrophoresis when in a number of runs the virtual separative migration distance and separation capability of the conditions used change widely. 相似文献
15.
Optimization of affinity capillary electrophoresis for routine investigations of protein–metal ion interactions
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Hassan A. Alhazmi Sami El Deeb Markus Nachbar Sabine Redweik Hassan M. Albishri Deia Abd El‐Hady Hermann Wätzig 《Journal of separation science》2015,38(20):3629-3637
To facilitate the implementation of affinity capillary electrophoresis into routine binding screening studies of proteins with metal ions, method acceleration, transfer and precision improvement were investigated. Affinity capillary electrophoresis was accelerated by using shorter capillaries, employing lower sample concentrations and smaller injection volumes. Intra‐ and inter‐instrument method transfers were investigated considering the temperature setting of the capillary cooling system. For intra‐instrument method transfer, similar results were obtained when transferring a method from a long (62 cm) to a short (31 cm) capillary. The analysis time was reduced from 9 to 4 min. In case of inter‐instrument method transfer, interaction results showed small variation on the capillary electrophoresis instrument with inefficient capillary cooling system. Binding measurement precision was enhanced by slightly pushing the sample above the beginning of the capillary. Changing the buffer vials after each 30 runs and employing extra flushing after each 60 subsequent runs further enhanced the precision. The use of 0.1 molar ethylenediaminetetraacetic acid in the rinsing solution successfully desorbs the remaining metal ions from the capillary wall. Excellent precision for apparent mobility ratio measurements was achieved for different protein–metal ion interactions (relative standard deviation of 0.16–0.89%, 15 series, 12 runs for each). 相似文献
16.
Spánik I Zebrowski W Májek P Skacáni I Krupcík J Armstrong DW 《Journal of separation science》2005,28(12):1347-1356
In this work, the capillary gas chromatographic enantiomer separation of eight congeneric compounds with general formulae CH3-HCX-COOC2H5 (where X = Cl, Br, I, CN, OH, OC2H5, OC6H5 and NHCOCF3) on four different permethyl- and 2,6-di-O-methyl-3-O-pentyl- beta- and gamma-CD stationary phases has been studied. The separation of enantiomers was evaluated in terms of the interactions of the X substituent of studied derivatives, as well as the nature of the 3-O-alkyl group in the 2,6-di-O-methyl-3-O-alkyl-CDs and the CDs cavity size. The differences in thermodynamic data [deltaH and -deltaS] obtained for studied compounds and the selectivity of modified beta- and gamma-cyclodextrin phases in gas chromatographic separation were evaluated. deltaH values were compared with a deltaH value of an achiral standard (ethyl propionate, where X = H) in order to obtain the contribution of a particular substituent to the overall interaction energy. It was shown that the variation in the enantiomeric separation with temperature and the retention order of these compounds on a given cyclodextrin capillary column depends on the nature of the substituents bonded to stereogenic carbon atom. It was found that the temperature dependencies of selectivity factors, In a on 1/T, were both linear as well as non-linear, inter alia depending on the number of glucopyranose units of the CD derivatives. The enantiospecific thermodynamic data [delta21(deltaH)] and [-delta21(deltaS)] which characterize the chiral recognition in the separation system were used to gain more insight into the mechanistic aspects of the enantioseparations on permethylated and 2,6-di-O-methyl-3-O-pentyl-beta- and gamma-cyclodextrins. 相似文献
17.
An axially illuminating whole-column fluorescence imaging capillary electrophoresis (CE) experimental setup was developed. A 6 cm long Teflon tube with an inside diameter (ID) of 42 microm was used as separation column. Excitation light of 488 nm from Ar+ laser was introduced to one end of the separation column by an optical fiber. The excitation light propagated inside the separation column by total internal reflection, since the refractive index of the buffer solution was larger than that of the Teflon tube. The fluorescence from the whole separation column was imaged with a charge-coupled device (CCD) camera. Fluorescent compounds such as fluorescein isothiocyanate (FITC), 5-carboxyfluorescein, and FITC-labeled protein were used to test the basic performance of the experimental setup. Experimental results illustrate that the whole-column-fluorescence imaging CE is a fast and sensitive separation method for fluorescent compounds and fluorescent-labeled proteins. Furthermore, it could be used for simple, fast, and easy comparisons of the resistance to photodegradation for various fluorescent compounds. 相似文献
18.
《Electrophoresis》2018,39(7):981-988
In this paper, we demonstrate the effectiveness of a new 3D printed magnet holder that enables capture of magnetic microparticles in commercially available capillary electrophoresis equipment with a liquid or air based coolant system. The design as well as the method to capture magnetic microparticles inside the capillary are discussed. This setup was tested at temperature and pH values suitable for performing enzymatic reactions. To demonstrate its applicability in CE‐ immobilized microenzyme reactors (IMER) development, human flavin‐containing monooxygenase 3 and bovine serum albumin were immobilized on amino functionalized magnetic microparticles using glutaraldehyde. These microparticles were subsequently used to perform in‐line capillary electrophoresis with clozapine as a model substrate. This setup could be used further to establish CE‐IMERs of other drug metabolic enzymes in a commercially available liquid based capillary coolant system. The CE‐IMER setup was successful, although a subsequent decrease in enzyme activity was observed on repeated runs. 相似文献
19.
Münch AS Seidel J Obst A Weber E Mertens FO 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(39):10958-10964
Recently developed MOF surface-coating techniques, the controlled SBU approach (CSA) for the generation of MOF-5, and the use of self-assembled monolayers have been combined to generate a wall-bonded, crosslinked stationary phase for gas chromatographic capillary columns displaying excellent performance in the separation of natural gas components. The chromatographic performance of this new type of column has been compared to the state-of-the-art solution for this separation problem, namely a coated silica column of the porous layer open tubular (PLOT) type. Chromatographic parameters such as separation, resolution, and tailing factors, as well as plate numbers and heights in the case of isothermal operation, have been determined. Kinetic and thermodynamic parameters characterizing the analyte-stationary phase interaction have been determined for various C1-C4 analytes. 相似文献
20.
《Journal of separation science》2018,41(12):2544-2552
The transfer of retention times based on thermodynamic models between columns can aid in separation optimization and compound identification in gas chromatography. Although earlier investigations have been reported, this problem remains unsuccessfully addressed. One barrier is poor predictive accuracy when moving from a reference column or system to a new target column or system. This is attributed to challenges associated with the accurate determination of the effective geometric parameters of the columns. To overcome this, we designed least squares‐based models that account for geometric parameters of the columns and thermodynamic parameters of compounds as they partition between mobile and stationary phases. Quasi‐Newton‐based algorithms were then used to perform the numerical optimization. In this first of three parts, the model used to determine the geometric parameters of the reference column and the thermodynamic parameters of compounds subjected to separation is introduced. As will be shown, the overall approach significantly improves the predictive accuracy and transferability of thermodynamic data (and retention times) between columns of the same stationary phase chemistry. The data required for the determination of the thermodynamic parameters and retention time prediction are obtained from fast and simple experiments. The proposed model and optimization algorithms were tested and validated using simulated and experimental data. 相似文献