Decades of chromatography research done with DryLab®.

Chromatographia · 2011

From Csaba Horváth to Quality by Design: Visualizing Design Space in Selectivity Exploration of HPLC Separations

Imre Molnár, K.E. Monks

The present paper starts by taking a look back at some of the pioneering work in high pressure liquid chromatography (HPLC) that went on in Csaba Horváth’s laboratory in 1970s, through the eyes of I. Molnár. It then goes on to describe a very modern approach to HPLC method development within the Quality by Design framework: the multifactorial optimization of three critical HPLC method parameters, i.e. gradient time (tG), temperature (T), and ternary composition (B1:B2) based on 12 experiments. The effect of these experimental variables on critical resolution and selectivity was carried out in such a way as to systematically vary all three factors simultaneously.

Chromatographia · 1984

Rapid measurement of cyclosporin a plasma levels by HPLC in allograft transplant recipients

H. Wilms, Imre Molnár

An HPLC-method for the measurement of blood Cyclosporin A levels (CyA) of renal allograft transplanted patients within 9min is described. After a simple protein precipitation of the blood the supernatant is transferred to an HPLC-system. The short time of analysis is obtained by a step gradient elution technique and a precolumn separation of the fractions of interest followed by a backflush regeneration step of the precolumn. The analysis of the fraction of interest takes place on a column with high resolution power as long as the precolumn is regenerated. CyA is monitored by UV-absorption at 206nm. Detection of 20 to 2000ng/ml CyA allows the use of the method for patient monitoring and for research purposes.

LC GC · 1998

Reversed-Phase Gradient Elution: How to Get Better Results with Less Work

Imre Molnár, Lloyd R. Snyder, John W. Dolan

LC GC · 1997

Selectivity Control in HPLC Method Development

Lloyd R. Snyder, John W. Dolan, Imre Molnár, N. M Djordjevic

LC GC · 1996

Validation of Robust Chromatography Methods Using Computer-Assisted Method Development for Quality Control I

Imre Molnár

LC GC · 1997

Validation of Robust Chromatography Methods Using Computer-Assisted Method Development for Quality Control II

Imre Molnár

LCGC North America · 2014

Quality by Design in Pharmaceutical Analysis Using Computer Simulation with UHPLC

Jenő Fekete, Róbert Kormány, Imre Molnár

In this study, the quality-by-design principle is applied instead of trial-and-error in the development of a liquid chromatography method. With few measurements, the appropriate stationary phase and chromatographic conditions such as the composition of mobile phase, gradient time, temperature, and pH can be determined. A mixture of an active pharmaceutical ingredient and its 13 impurities was analyzed on a short narrow-bore column (50 mm × 2.1 mm, packed with sub-2-µm particles) providing short analysis times. The performance of commercial modeling software for robustness testing was systematically compared to experimental measurements and design-of-experiment–based predictions.

American Chemical Society, Middle Atlantic Regional Meeting, Proceedings, 261 · 2008

Computerized Design of Robust Gradient HPLC Methods

Imre Molnár, Hans-Jürgen Rieger

PZ (Pharmazeutische Zeitung) Wissenschaft · 1992

Determination of by products in atenolol

H. Hofmann, Imre Molnár

The method described in this paper was developed with the help of the gradient elution technique. With known dwell volume, gradient elution could b...

LaborPraxis · 2010

Computergestützte Methodenentwicklung in der HPLC

Steffen Wiese, Thorsten Teutenberg, Torsten C. Schmidt, Hans-Jürgen Rieger, Imre Molnár

In den letzten Jahren wurde eine Reihe von Verfahren entwickelt, für die eine Temperaturgradientenelution in der Flüssigchromatographie unumgänglich ist. Lesen Sie, wie bereits existierende Retentionsmodelle angepasst werden können, um HPLC-Methoden mittels Temperaturgradientenelution unter isokratischen Bedingungen zu entwickeln.

Journal of Pharmaceutical and Biomedical Analysis · 2011

Expanding the term “Design Space” in high performance liquid chromatography (I)

Kate E. Monks, Hans-Jürgen Rieger, Imre Molnár

The current article presents a novel approach to applying Quality by Design (QbD) principles to the development of high pressure reversed phase liquid chromatography (HPLC) methods. Four common critical parameters in HPLC – gradient time, temperature, pH of the aqueous eluent, and stationary phase – are evaluated within the Quality by Design framework by the means of computer modeling software and a column database, to a satisfactory degree. This work proposes the establishment of two mutually complimentary Design Spaces to fully depict a chromatographic method; one Column Design Space (CDS) and one Eluent Design Space (EDS) to describe the influence of the stationary phase and of the mobile phase on the separation selectivity, respectively. The merge of both Design Spaces into one is founded on the continuous nature of the mobile phase influence on retention and the great variety of the stationary phases available.

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.

Chromatographia · 2005

Searching for Robust HPLC Methods – Csaba Horváth and the Solvophobic Theory

Imre Molnár

This paper is written in remembrance of the work of Csaba Horváth on Reversed Phase Chromatography, (RPC) and the fundamental theory of the mechanism of retention on non-polar stationary phases, the ``Solvophobic Theory''. The paper discusses some steps in the development of this important theory and examines its consequences in developing robust methods for routine RPC. Reliable product quality requires the understanding of selectivity changes, which in RPC govern the development of robust and reliable methods involving continuous changes of liquid chromatographic parameters in aqueous eluents. The application of RPC is still growing in scientific research and in pharmaceutical and chemical production. The impact of the Solvophobic Theory in life sciences has been enormous but it was only a part of Horváth's scientific work. RPC is today one of the most popular, most widely used tools in analytical chemistry and will remain so for many years due to its stability and to its robustness.

Webpage · 2025

Leveraging Multidimensional Modeling to Resolve Frequent Separation Challenges in HPLC | LCGC International

Arnold Zöldhegyi, Róbert Kormány, Szabolcs Fekete, Krisztián Horváth, Imre Molnár

High performance liquid chromatography (HPLC) is a widely used and well-established technique, routinely employed by thousands of analytical scientists worldwide. Nonetheless, certain challenges—arising from the complex interplay of multiple factors affecting peak retention and separation—persist. In this context, multidimensional modeling approaches can provide valuable support.

Journal of Pharmaceutical and Biomedical Analysis · 2018

Automated UHPLC separation of 10 pharmaceutical compounds using software-modeling

Arnold Zöldhegyi, Hans-Jürgen Rieger, Imre Molnár, Liliya Fekhretdinova

Human mistakes are still one of the main reasons of underlying regulatory affairs that in a compliance with FDA’s Data Integrity and Analytical Quality by Design (AQbD) must be eliminated. To develop smooth, fast and robust methods that are free of human failures, a state-of-the-art automation was presented. For the scope of this study, a commercial software (DryLab) and a model mixture of 10 drugs were subjected to testing. Following AQbD-principles, the best available working point was selected and conformational experimental runs, i.e. the six worst cases of the conducted robustness calculation, were performed. Simulated results were found to be in excellent agreement with the experimental ones, proving the usefulness and effectiveness of an automated, software-assisted analytical method development.

Journal of Chromatography B: Biomedical Sciences and Applications · 1997

Computerized optimization of the high-performance liquid chromatographic enantioseparation of a mixture of 4-dinitrophenyl amino acids on a quinine carbamate-type chiral stationary phase using drylab

Michael Lämmerhofer, Paolo Di Eugenio, Imre Molnár, Wolfgang Lindner

A method is proposed for the sensitive chiral analysis of amino acid enantiomers by high-performance liquid chromatography (HPLC). Thus the enantiomers of a mixture of seven racemic amino acids were resolved as their DNP derivatives from each other and from the peak of the hydrolyzed reagent, employing a quinine carbamate-based chiral anion exchange-type chiral stationary phase (CSP) and aqueous buffered mobile phases. However, the initial isocratic chromatogram yielded many peak overlaps although the corresponding enantiomers were well resolved. Therefore, the separation of the complex mixture had to be optimized; we utilized the commercial computer method development software drylab. First, the influence of the manifold mobile phase parameters and chromatographic conditions (pH, type and content of organic modifier, buffer concentration, temperature, type of co-ion, etc.) on retention and resolution was studied by isocratic elution. Furthermore, with such optimized conditions linear and multi-segmented organic modifier and buffer salt gradients, respectively, were simulated with the computer program and experimentally verified. Average errors of prediction of retention times lay between 2 and 8%. Finally, a highly improved HPLC gradient method resulted in almost all components being baseline separated and equally spaced and accelerated by a factor of more than 3 compared to the initial run.

Journal of Chromatography A · 1996

High-performance liquid chromatographic separation of the impurities in a pharmaceutical raw material with the aid of computer simulation

H. W. Bilke, Imre Molnár, Ch. Gernet

A complex pharmaceutical raw material was characterized by means of reversed-phase gradient elution. By varying gradient steepness and mobile-phase pH, it was possible to optimize band spacing so as to separate 16 impurities or degradation products from the drug substance. Computer simulation was useful in interpreting these complex chromatograms and determining the maximum number of peaks that could be separated in this way. A marginal separation of all 17 sample components could be obtained, but the resulting method was quite pH-sensitive and therefore not very rugged. As an alternative, a rugged method was developed that separates the drug substance from all other sample components. The present study also describes how present computer simulation software for isocratic separation can be used to predict resolution for gradient elution runs as a function of pH.

CRC Press · 2021

Advances in Chromatography: Volume 57

Nelu Grinberg, Peter W. Carr

Journal of Chromatography A · 2026

Retention modeling of oligonucleotides on an amide-based HILIC column: A descriptor-driven approach

Jonathan Maurer, Balasubrahmanyam Addepalli, Fabrice Gritti, Matthew A. Lauber, Davy Guillarme, Szabolcs Fekete

Hydrophilic interaction chromatography (HILIC) has recently gained attention as a powerful tool for the analysis of nucleic acid–based therapeutics, offering high resolving power and excellent compatibility with mass spectrometry. However, the successful development of HILIC methods requires a clear understanding of the underlying retention mechanisms. Despite numerous studies, the respective contributions of hydrophilic partitioning, polar interactions, and ionic interactions to oligonucleotide retention remain poorly understood. In this work, the role of hydrogen bonding, dipole-dipole interactions, solvophobic effects, and ionic interactions in governing oligonucleotide retention have been systematically investigated. A series of targeted design-of-experiments studies, performed on a representative panel of samples to investigate the impact of oligonucleotide structure on retention, provided a refined framework for interpreting HILIC separations of oligonucleotides. All experiments were performed on an amide-bonded stationary phase, and the proposed descriptor-based retention model applies specifically to this surface chemistry. Our results demonstrate that solvophobic effects and hydrogen bonding are the dominant drivers of retention, whereas hydrophilic partitioning contributes negligibly under practical conditions. This mechanistic insight has important consequences for method development: introducing protic solvents into the mobile phase, conditions that would disrupt the water-rich layer, substantially increases selectivity and enables the resolution of closely related oligonucleotide species. Altogether, these findings shift the conceptual basis of HILIC for nucleic acids from a hydrophilic partitioning/interaction model toward a retention mechanism best described as a solvophobic–interaction‑dominated HILIC regime, in which protic solvents assist selectivity through H‑bond competition. This new perspective provides a more accurate foundation for designing, optimizing, and interpreting HILIC methods for oligonucleotide analysis.

Journal of Liquid Chromatography & Related Technologies · 2013

Analysis of Sulfonamide Residues in Real Honey Samples Using Liquid Chromatography with Fluorescence and Tandem Mass Spectrometry Detection

Ádám Tölgyesi, Róbert Berky, Katalin Békési, Szabolcs Fekete, Jenő Fekete, Virender K. Sharma

This paper presents new reversed phase liquid chromatographic methods (HPLC-FLD and LC-MS/MS) for the quantification of sulfonamides in spiked and incurred honey samples. The sample preparation was optimized using Oasis HLB (hydrophilic–lipophilic balance) solid-phase extraction (SPE) cartridge. Elutions of sulfonamides were carried out under acidic, neutral, and basic conditions using methanol. Recoveries under acid condition were in the range from 66.8–90%, which were approximately 10% higher than those obtained under other conditions. The sample clean-up was also tested using Strata-XL cartridges. The HPLC-FLD separation was performed using a Varian C18 column and a ternary (methanol-acetonitrile-phosphate buffer, pH 5) mobile phase resulting good selectivity for the determination. The robustness of the ternary gradient method was evaluated by computer simulation (DryLab). LC-MS/MS separation was carried out on a Kinetex XB core-shell type HPLC column that enabled a low limit of detection (0.01–0.5 µg/kg) and faster separation (6 min). The developed methods were validated in accordance with the European Union Commission Decision 2002/657/EC and were applied successfully for more than four hundred honey samples (under a national monitoring program). The concentrations of sulfadimethoxine, sulfachloropyridazine, and trimethoprim residues in samples were found in a concentration range from 0.03 up to 686 µg/kg.