ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Optimizing separations in reversed-phase liquid chromatography by varying pH and solvent composition (1993)
    Springer
    Chromatographia 35 (1993), S. 18-32 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reverse phase ; Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An interpretive optimization procedure in which pH can be one of the variables is presented with the emphasis on optimizing separations. When varying the pH in reversed-phase liquid chromatography the retention of ionogenic solutes will change. Thus, the selectivity between ionogenic and neutral solutes or between ionogenic solutes mutually can be optimized. However, pH also greatly affects the efficiency (plate count) and peak shape (asymmetry). Optimum selectivity (i.e. large differences in retention times) may be observed under conditions where peaks are broad and asymmetrical. Thus, it is essential to simultaneously consider retention, peak width and peak shape and their effects on separation (effective resolution) in pH-optimization studies. A procedure in which this is done is presented and applied to optimizing the separation of a synthetic mixture of selected pharmaceuticals. After initial experiments to establish the parameter space (boundaries for pH and binary methanol — water composition), twelve experiments are performed according to a 3×4 experimental design. At each loaction the retention, peak height, peak area and peak symmetry are recorded for each solute. These data are then used to build models for each of the four characteristics and for each solute. From this set of models the response surface, describing the quality of separation as a function of pH and composition, can be calculated. A variety of optimization criteria (quantifying quality of separation) can be used. The optimum corresponds to the highest point on the response surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02278552
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    The solubility parameter as a tool in understanding liquid chromatography (1982)
    Springer
    Chromatographia 15 (1982), S. 205-214 
    Details
    ISSN: 1612-1112
    Keywords: Solubility parameter ; Theory of liquid chromatography ; Retention ; Selectivity ; Specific effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The solubility parameter concept is briefly discussed. It is then used to explain some of the current features of liquid partition and adsorption chromatography. Various phase systems are discussed on the basis of three characteristics.retention, selectivity (the general separation power of a system) andspecificity (increased separation power towards certain pairs of solutes). The emergence of two essentially different techniques, the ‘normal phase’ and ‘reversed phase’ modes, will appear as a logical consequence of simplified theory. It also becomes obvious why ‘reversed phase’ applications are so much more numerous. Some suggestions are given for the development of new stationary phases and the improvement of existing ones. The usefulness of the solubility parameter concept to predict the solvent strength of mixed eluents in reversed phase liquid chromatography (RPLC) is demonstrated. Some practical rules for the selection and operation of stationary and mobile phase systems are formulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02261542
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    An expert system for the selection of criteria for selectivity optimization in high-pressure liquid chromatography (1988)
    Springer
    Chromatographia 26 (1988), S. 101-109 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Expert systems ; Selectivity optimization ; Optimization criteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Systematic procedures for the optimization of chromatographic selectivity require objective criteria to characterize the quality of separation in a chromatogram. Numerous criteria have been suggested. Different criteria yield different results and the choice will depend on a large number of factors. It is genuinely difficult to select the most suitable criterion in a particular situation. For these reasons, an expert system has been developed to assist chromatographers in the selection of optimization criteria. A structured representation of the required knowledge and its implementation in an expert-system shell are presented in this paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02268132
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    An improved optimization procedure for the selection of mixed mobile phases in reversed phase liquid chromatography (1982)
    Springer
    Chromatographia 16 (1982), S. 48-52 
    Details
    ISSN: 1612-1112
    Keywords: RP-HPLC ; Optimization ; Complex mobile phases ; Iso-eluotropic mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The stepwise procedure described previously [1] for the selection of optimal mobile phase compositions in reversed phase liquid chromatography (RPLC) is improved in two ways. The optimization criterion is modified to account for variations in analysis time. The iterative approach to the optimal solvent composition makes a more efficient use of previous data. An example illustrates the resulting gain in speed and accuracy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02258868
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    An expert system for the optimization of columns, operating conditions and instrumentation for high-pressure liquid chromatography (1988)
    Springer
    Chromatographia 26 (1988), S. 37-44 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Expert systems ; Optimization of operating parameters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Given the mobile and the stationary phase and values for the physical parameters such as temperature and pH, a separation can be optimized by varying the so-calledchromatographic parameters. These include the column dimensions, particle size, operating conditions (e.g. flow rate, attenuation) and instrumentation (e.g. detector cell, time constant). Optimization of the chromatographic parameters implies finding the best possible set of values, which we define as yielding (i) sufficient separation and (ii) sufficient sensitivity in (iii) the shortest possible time. Finding the best possible conditions (the global optimum) is very difficult for chromatographers in practice. An expert system is described that allows chromatographic optimization to be performed for isocratic separations. An initial chromatogram is required to consult the system. In return, the system provides a complete set of chromatographic parameters, which represents the global optimum within the limits set by the required resolution and signal-to-noise ratio specified by the user. The tolerated flow and pressure ranges, the volume of the available detector cells and the time constant of the detection system are constraints during the optimization. A separate module of the system concerns the sample preparation for pharmaceutical formulations in solid dosages and aqueous solutions. Prototype expert systems have been successfully implemented in the expert-system shell Knowledge Craft on a MicroVAX workstation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02268122
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Modelling chromatographic behaviour as a function of pH and solvent composition in RPLC (1993)
    Springer
    Chromatographia 36 (1993), S. 83-95 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Retention models ; Method development ; pH optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this work we establish the basic layout of IONICS, an expert system for optimizing the separation of ionogenic solutes in Reversed-Phase Liquid Chromatography, using the pH and the organic-modifier concentration of the mobile phase as parameters. We also present REMO, a front-end system that automates the retention modelling stage, based on a 9-parameter model. This system uses a scale transformation to suppress several numerical problems previously observed and features a strategy for automatic calculation of an initial approximation to the model optimum. The successful application of this system to a set of seven drugs is described. The final models are accurate and have smaller numerical problems. We also describe the use of a genetic algorithm instead of classical non-linear least-squares for fitting the model to the experimental data. Results indicate that genetic algorithms are a valuable, complementary tool for retention modelling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02263843
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Die Löslichkeitsparameter als Werkzeug zum Verständnis der Flüssigkeitschromatographie (1982)
    Springer
    Chromatographia 15 (1982), S. 387-398 
    Details
    ISSN: 1612-1112
    Keywords: Solubility parameter ; Theory of liquid chromatography ; Retention ; Selectivity ; Specific effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Das Konzept des Löslichkeitsparameters wird kurz diskutiert. Danach wird es benutzt, um einige Erscheinungen der Flüssig/Flüssig-Verteilungs-(LLC) und Adsorptions-Chromatographie (LSC) zu erklären. Es werden unterschiedliche Phasensysteme bezüglich dreier charakteristischer Erscheinungen besprochen:Retention, Selektivität (erhöhte Trennkraft eines Systems) undSpezifität (erhöhte Trennkraft für bestimmte Substanzpaare). Die Erscheinung zweier wesentlich unterschiedlicher Techniken, der Normalphasen- und der Umkehrphasen-Technik, ergibt sich als logische Konsequenz der vereinfachten Theorie. Es wird auch klar, warum die Reversed Phase. Anwendungen sehr viel zahlreicher als die übrigen sind. Es werden einige Anregungen zur Entwicklung neuer stationärer Phasen und der Verbesserung der bereits bestehenden gegeben. Es wird dargestellt, wie nützlich das Löslichkeitsparameter-Konzept zur Vorhersage der Lösemittelstärke von Lösemittelgemischen in der Umkehrphasen-Chromatographie ist. Zum Schluß werden einige praktische Regeln zur Auswahl und dem Betrieb von stationären und mobilen Phasensystemen formuliert.
    Notes: Summary The solubility parameter concept is briefly discussed. It is then used to explain some of the current features of liquid partition and adsorption chromatography. Various phase systems are discussed on the basis of three characteristics:retention, selectivity (the general separation power of a system) andspecificity (increased separation power towards certain pairs of solutes). The emergence of two essentially different techniques, the ‘normal phase’ and ‘reversed phase’ modes, will appear as a logical consequence of simplified theory. It also becomes obvious why ‘reversed phase’ applications are so much more numerous. Some suggestions are given for the development of new stationary phases and the improvement of existing ones. The usefulness of the solubility parameter concept to predict the solvent strength of mixed eluents in reversed phase liquid chromatography (RPLC) is demonstrated. Some practical rules for the selection and operation of stationary and mobile phase systems are formulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02259227
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    A simple procedure for the rapid optimization of reversed-phase separations with ternary mobile phase mixtures (1982)
    Springer
    Chromatographia 15 (1982), S. 688-696 
    Details
    ISSN: 1612-1112
    Keywords: Reversed-phase LC ; Ternary mobile-phases ; Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple rapid procedure is described for estimating optimum compositions of ternary mobile phase mixtures for the separation of samples by reversed-phase liquid chromatography (RPLC). Retention data in two iso-eluotropic binary mobile phase mixtures (mixtures with equal retention times) are required to initiate the procedure. The logarithm of the capacity factor is assumed to vary linearly with the composition of isoeluotropic ternary mixtures formed by mixing the two limiting binaries. Using the product of resolution factors of adjacent peaks as the criterion, an optimum ternary composition is then calculated. After a chromatogram has been obtained with the predicted optimum ternary mobile phase, the procedure is repeated until no further improvement can be achieved. Examples of the application of the present procedure are described to illustrate its effectiveness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02261886
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    An overview of contemporary method development in liquid chromatography (1988)
    Springer
    Chromatographia 25 (1988), S. 737-748 
    Details
    ISSN: 1612-1112
    Keywords: Method development ; System selection and optimization ; Selectivity optimization ; Method validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper provides an overview of method development in liquid chromatography. It is explained why every practicing chromatographer needs to understand the process of method development. Thus, this paper is directed towards chromatographers who develop new separation methods, as well as to those who apply published methods. The method-development process is first explained in broad terms, after which the different aspects of the process are described in more detail. First, attention is paid to the initial stages of method development, which consist of the accurate definition of the separation problem and the selection of the most suitable chromatographic method. Method-development expert systems are discussed with regards to their applicability in this area. Selectivity optimization is shown to rely on three main factors,i. e. the selection of the parameter space, the experimental design and the optimization criterion. Selectivity-optimization procedures are described very briefly. System optimization concerns those factors which do not affect the chemistry of the system (mobile and stationary phase), but are essentially determining the analysis time and the sensitivity. The method-validation stage can be divided into three main parts: qualitative method validation (i.e. peak integrity and identity), calibration and quantitative method validation. The requirements of calibration procedures are briefly reviewed and an inventory of method-validation procedures is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290483
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    A fundamental study of the effects of modifiers in supercritical fluid chromatography (1989)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 12 (1989), S. 645-651 
    Details
    ISSN: 0935-6304
    Keywords: Supercrittical fluid chromatography, SFC ; Packed columns ; Modifiers ; Adsorption isotherms ; Reaction model ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of organic modifiers on retention and peak shape in packed-column supercritical fluid chromatography were studied. The adsorption behavior of different modifiers was investigated on stationary phases consisting of hydrocarbon monolayers chemically bonded on silica. Adsorption isotherms for several modifiers were recorded using breakthrough measurements. The results were compared with those obtained by a simple method based on the injection of different sample sizes. Modifiers were selected to reflect various types of interactions with the silica support. Isotherms were found to be approximately Langmuirean. Experiments were performed to elucidate the influence of adsorbed molecules on the retention of selected test solutes.The introduction of a solvent modifier can lead to a substantial change in the mobile phase density, the effect of which is comparable with that of an increase in the density of pure carbon dioxide. Our results confirm that the effects of low concentrations of modifiers (between 0 and 2 percent) in packed-column SFC are largely due to deactivation of residual silanol groups on the silica support. The accessibility of the active sites was found to depend strongly on the size and structure of the modifier molecules. The decrease of retention due to the addition of low concentrations of modifiers could be described accurately by a model derived from Langmuir adsorption behavior. Some semi-quantitative rules for the selection of modifiers and the required concentrations for optimum deactivation of the support are discussed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240121003
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...