Decades of chromatography research done with DryLab®.

Journal of Chromatography A · 2001

Computer-assisted high-performance liquid chromatography method development with applications to the isolation and analysis of phytoplankton pigments

Laurie Van Heukelem, Crystal S Thomas

We used chromatography modeling software to assist in HPLC method development, with the goal of enhancing separations through the exclusive use of gradient time and column temperature. We surveyed nine stationary phases for their utility in pigment purification and natural sample analysis. For purification, a complex algal matrix was separated on an efficient monomeric column, from which partially purified fractions were collected and purified on polymeric columns that exaggerated resolution between pigments of interest. Additionally, we feature an HPLC method that is simple, fast, demonstrates excellent transferability and is ideal for quantitative analysis of pigments in dilute natural water samples.

LC GC Europe · 2002

Optimizing Multilinear Gradients in HPLC

Tom H. Jupille, Lloyd R. Snyder, Imre Molnár

Multilinear gradients have not been widely used in general purpose high performance liquid chromatography, in part because of experimental inconvenience in method development. Even with the use of computer modelling, identifying an optimum set of breakpoints has primarily been done by trial and error. Combining a spreadsheet with controllable chromatography modelling software has allowed us to implement a systematic approach to bi- and tri-linear gradient optimization. Application of this approach to 10 randomly generated sample sets suggests that the improvement in critical resolution that can be obtained is considerably smaller than that obtained through the use of a second selectivity variable. Because no additional experimental time (and only limited computational time) is required once an optimum linear gradient has been modelled, however, any improvement thus gained is essentially "free".

Chromatographia · 2012

Computer-Assisted HPLC Method Development for Determination of Tolmetin and Possible Kinetic Modulators of Its Oxidative Metabolism in Vivo

Rasha Hanafi, Hilde Spahn-Langguth, Laila Mahran, Ola Heikal, Abeer Hanafy, Hans Rieger, Imre Molnár, Hassan Y. Aboul-Enein

Following administration of the acidic drug tolmetin (TOL) anaphylactic reactions occurred, which have been hypothesized to be related to the formation of reactive acyl glucuronides. Recently, glutathione adducts have been detected upon incubation of TOL with human liver microsomal preparations, which proved that oxidative activation might also be a pathway of formation of reactive—possibly toxic—glutathione metabolites of TOL. The aim of this work was to develop a new and robust HPLC method to investigate the in vivo effect of 2 coadministered drugs/nutritional supplements on the kinetics of TOL in rats (cimetidine; CIM) known to be a potent inhibitor of CYP3A4, an enzyme that catalyzes the oxidative metabolism and Quercetin; and QUE which induces UGT1A6, an enzyme involved in glucuronidation of acidic drugs. DryLab®, a computer simulation software package, was used to assist in the development and optimization of the HPLC method used for separation of TOL and the two potential kinetic modulators together with three potential internal standards (zomepirac, carvedilol and fexofenadine). The method was validated in biological samples obtained from rats. Non-compartmental pharmacokinetic analysis of data obtained from plasma and rat liver tissue showed significantly higher concentrations of TOL in the presence of CIM; and significantly longer elimination half-life lives in presence of QUE, which implies that drugs or food components interacting with CYP3A4 cause alteration in the metabolic oxidative biotransformation of TOL in vivo leading to accumulation of TOL in the body through a decrease of its clearance. These findings might account for to the side-effects associated with TOL when co-administered with such kinetic modulators.

Journal of Chromatography A · 2002

Advanced high-performance liquid chromatography method development: Discovering unexpected choices in chromatography

Imre Molnár, Hans-Jürgen Rieger

The influence of some important experimental parameters on the resolution of compounds as well as the validity of widely used rules of thumb and of common expectations about how to improve resolution is discussed. It will be shown, on the basis of selected examples, that the general expectations about how the experimental parameters have to be adjusted for better resolution does not cover all chances for resolution improvement. The tool for understanding the method and to discover all chances for increasing selectivity is the resolution map of a method.

Journal of Chromatography · 1989

Development of a high-performance liquid chromatographic method for fluroxypyr heerbicide and metabolites using computer simulation with drylab software

R. G. Lehmann, J. R. Miller

The herbicide fluroxypyr 1-methylheptyl ester was separated from its acid form (fluroxypyr) and two soil metabolites (a pyridinol and a methoxypyridine) by high-performance liquid chromatography (HPLC) with the acid of Drylab G. A difference in retention time of at least 6 min between each compound was achieved, to allow complete separation of radiolabeled components during collection of 1-min fractions. The total elution time was 31 min. Actual HPLC retention times differed from DryLab G predictions by 0.5 min or less.

Journal of Chromatography A · 1996

Determination of 1,8-dihydroxyanthranoids in senna

Wolfgang Metzger, Klaus Reif

This paper describes the results of a new method for the determination of 1-,-hydroxyanthranoids in senna. This will be illustrated by examples from a study of the occurrence of 17 different 1,8-dihydroxyanthranoids (anthraquinones and their bianthrys) in fruits leaves of PSenna angustifolia amd Senna acutifolia. The anthranoids are extracted using a mixture of acetonitrile and a solution of sodium hydrogencarbonate. The different compounds are separated and detected by HPLC using an Rp-8 column and a photodiode array detector. The method was optimized by means of computer-assisted method development techniques using the DryLab software.

LC Magazine · 1984

Reciprocating Piston Pumps

Berry, Vern V. Dolan, John W.

Journal of Chromatography · 1991

Computer simulation as an aid in method development for gas chromatography: III. Examples of its application

L. R. Snyder, D. E. Bautz, J. W. Dolan

The use of computer simulation for developing optimized gas chromatographic (GC) separations is illustrated for several samples. Resolution maps (plots of Rsvs. heating rate r) for different starting temperatures provide a means for the rapid exploration of separation as a function of the temperature program in the case of programmed-temperature GC. Isothermal separations are easily developed by trial and error, because of the speed of computer simulation. More complex samples may require multi-ramp temperature programs; these require a greater method development effort, but partial resolution maps can help facilitate this process.

Journal of Chromatography · 1991

Computer simulation as an aid in method development for gas chromatography: II. Changes in band spacing as a function of temperature

J. W. Dolan, L. R. Snyder, D. E. Bautz

Several different samples and three stationary phases of varying polarity have been examined for changes in band spacing as a function of temperature. The results of these studies have been expressed as a relative variability in the temperature coefficients of retention (S) for adjacent bands. A theoretical analysis suggests that useful changes in band spacing vs. temperature (or heating rate) can be expected when the difference in S values (ΔS) for two bands is larger than 1 to 2%. The samples studied exhibited variations in average values of ΔS of 0.6–6%. This suggests that optimizing the (isothermal) temperature or (programmed) heating rate of a gas chromatographic separation will often be advantageous.

Journal of Chromatography · 1991

Computer simulation as an aid in method development for gas chromatography: I. The accurate prediction of separation as a function of experimental conditions

D. E. Bautz, J. W. Dolan, L. R. Snyder

Computer-simulation with commercially available software (DryLab GC) allows the prediction of isothermal or temperature-programmed gas chromatographic (GC) separation as a function of experimental conditions. In either case, two experimental runs are carried out initially, using a linear temperature program (heating rate different, all other conditions the same). Data from these two runs are entered into the computer, and separation can then be predicted for other conditions: different temperatures in the case of isothermal runs, or any kind of temperature program for programmed runs. The reliability of resulting predictions was evaluated in the present study for several samples and a wide ranger in separation conditions. Retention time predictions were usually accurate within a few percent, and sample resolution was predicted within about ± 10%. The use of computer simulation should be a considerable help for the rapid development of superior GC methods.