Literature | MOLNÁR-INSTITUTE

Journal of Chromatography A · 2013

Determination of alcohols in essential oils by liquid chromatography with ultraviolet detection after chromogenic derivatization

Juan Ródenas-Montano, Enrique J. Carrasco-Correa, Miriam Beneito-Cambra, Guillermo Ramis-Ramos, José Manuel Herrero-Martínez

An HPLC-UV method to determine compounds having a hydroxyl functional group in plant essential oils is developed. The sample is diluted with 1,4-dioxane and the analytes are derivatized with phthalic anhydride. The derivatives (phthalates hemiesters) are separated on a C8 column using an acetonitrile (ACN)/water gradient. Separation conditions were optimized using the DryLab® method development software. For the alcohols and phenols present in mint and rose essential oils, optimization led to a ca. 40min gradient time and a column temperature of 8°C. The alcohol and its derivatives were identified using HPLC with mass spectrometry (MS) detection. A large sensitivity enhancement was obtained by derivatization protocol. The HPLC-UV method was compared to GC with flame ionization detector (FID) and GC–MS. The limits of detection (LODs) obtained by the proposed method were better than those obtained by GC-FID and of the same order as those achieved by GC–MS. The three methods were satisfactorily applied to the determination of alcohols in essential oils. Therefore, the recommended method is of interest as an alternative to GC methods, to investigate the presence of compounds having an alcohol group at low concentrations in essential oils.

Journal of Pharmaceutical and Biomedical Analysis · 2013

Using an innovative Quality-by-Design approach for development of a stability indicating UHPLC method for ebastine in the API and pharmaceutical formulations

Alexander H. Schmidt, Imre Molnár

A stability-indicating ultra high performance liquid chromatographic (UHPLC) method has been developed for purity testing of ebastine and its pharmaceutical formulations. Successful chromatographic separation of the API from impurities was achieved on a Waters Acquity UPLC BEH C18, 50mm×2.1mm, 1.7μm particle size column with gradient elution of 10mM acetate buffer pH 6.2 and a mixture of acetonitrile/2-propanol (1:1) as the mobile phase. Incorporating Quality by Design (QbD) principles to the method development approach by using the chromatography modeling software DryLab®4 allows the visualization of a “Design Space”, a region in which changes to method parameters will not significantly affect the results as defined in the ICH guideline Q8 (R2). A verification study demonstrated that the established model for Design Space is accurate with a relative error of prediction of only 0.6%. The method was fully validated for specificity, linearity, accuracy and precision, and robustness in compliance to the ICH guideline Q2 (R1). The method was found to be linear in the concentration range from the quantification limit (LOQ) to 125% of the specification limit for ebastine and each of the impurities with correlation coefficients of not less than 0.999. The recovery rate was between 98.15 and 100.30% for each impurity. The repeatability and intermediate precision (RSD) were less than 3.2% for ebastine and each of the impurities. The robustness of the developed method was studied by varying the six parameters: gradient time, temperature, ternary composition of the eluent, flow rate and start and end concentration of the gradient at 3 levels (+1, 0, −1). The resulting 729 experiments were performed in silico from the previously constructed model for Design Space and showed that the required resolution of 2.0 can be reached in all experiments. To prove the stability-indicating performance of the method, forced degradation (acid and base hydrolysis, oxidation, photolytic and thermal stress conditions) of ebastine was carried out. Baseline separation could be achieved for all peaks of the impurities, the degradation products and the API. Total run time was only 4min, which is an impressive 40-fold increase in productivity in comparison to the method published in the Ph. Eur. monograph and allowed purity testing of more than 360 samples per day.

Journal of Pharmaceutical and Biomedical Analysis · 2013

Comparison of supercritical fluid chromatography and reverse phase liquid chromatography for the impurity profiling of the antiretroviral drugs lamivudine/BMS-986001/efavirenz in a combination tablet

A. J. Alexander, L. Zhang, T. F. Hooker, F. P. Tomasella

Dual and triple combinations of antiretroviral drugs are a cornerstone of human immunodeficiency virus type 1 (HIV-1) treatment. Supercritical fluid chromatography (SFC) and reverse phase liquid chromatography (RPLC) methods have been developed for the impurity profiling of a prototype combination tablet containing three such drugs: lamivudine, BMS-986001 and efavirenz. Separation by SFC was achieved using a Princeton 2-ethyl pyridine stationary phase and a mobile phase B consisting of methanol with 10mM ammonium acetate and 0.1% isopropyl amine. This combination of mobile phase additives was required for both the separation of minor components and to minimize peak tailing of the active pharmaceutical ingredients (APIs). Separation by RPLC was achieved using a Discovery HSF5 stationary phase and a mobile phase consisting of 10mM ammonium acetate, pH 5.5 and methanol. Mobile phase gradient elution was employed in each case to elute components with a wide range of polarities. Both these methods were found to have advantages and disadvantages. Out of the three APIs and 13 possible impurity/degradation products selected, all were resolved by RPLC. By SFC, 15 peaks were resolved with one co-eluting pair and a high degree of orthogonality was achieved relative to RPLC. A more even distribution of peaks across the separation space, a non-sloping baseline and fewer system peaks were significant advantages associated with the SFC method. Particular attention had to be paid to optimizing the reverse phase diluent strength/initial mobile phase composition to avoid distortion of the peak shapes for early eluting components. This was not an issue with SFC, as the diluent of choice (methanol) was also the solvent of choice (in combination with ≤20% water) for the dissolution of the triple combination tablet. As with RPLC, SFC was found to exhibit the required sensitivity for successful quantitation of potential impurities/degradation products at the 0.05–0.1 area% level.

Journal of Chromatography A · 2013

Intergroup cross-comparison for the evaluation of data-interchangeability from various chromatographic tests

Chamseddin Chamseddin, Imre Molnár, Thomas Jira

The recently dramatic increase in the available choices of reversed-phase columns could be an advantage of this mode of separation. However, due to the insufficiency of available information in terms of the exact functionality of these phases and the similarities and differences between these newly introduced and conventional reversed-phase columns, it is now somehow problematic to determine which could be the best column for a given analytical problem. There is no single column that will give us a good separation for all applications. As a result, there have been several attempts to develop testing strategies to characterize column chemistries. In this study three of the most widely used and acceptable approaches for the characterization of reversed-phase columns, which are Tanaka, United States Pharmacopeia (USP), and Snyder–Dolan, are systemically applied to investigate the chromatographic properties of calixarene- and resorcinarene-bonded stationary phases, polar-embedded and polar-endcapped stationary phases, phenyl and ether-linked phenyl with the presence of conventional alkyl-bonded phases (octyl- and octadecylsilane). Although all column classification systems aim to evaluate “more or less” the same characteristics, each system uses different test mixtures in different chromatographic conditions. It is therefore very important to evaluate the similarities and differences in the resulted “column parameters” and the possible interchangeability of them. The results of this comparative study show that the used parameters of Tanaka and of Snyder–Dolan have in many cases a good to very good correlation. The USP approach, which is based on single run, is related to Tanaka and Snyder–Dolan only in terms of hydrophobic characters, and no relation could establish in the other parameters. The hydrophobic-subtraction model could be extended to describe the ligand–solute interactions of calixarene- and resorcinarene-bonded stationary phases, which are belonging to reversed phase material. However they show, depending on the analytes, some additional interactions, since their steric, polar and ionic properties are different compared to those of conventional alkyl-bonded phases.

LCGC Supplements · 2013

Application of Quality by Design Principles to a Pharmaceutical Sample Using UHPLC Method Development with Modeling Technologies

Hans-Jürgen Rieger, Róbert Kormány, Imre Molnár

A new type of method development that uses modeling to find the "best" separation for high performance liquid chromatography (HPLC) was investigated and principles of Quality by Design (QbD) were followed when planning the investigation. The process delivered precise results and the method was able be transferred to a routine quality control (QC) laboratory.

Journal of Separation Science · 2013

Determination of the design space of the HPLC analysis of water-soluble vitamins

Hebatallah A. Wagdy, Rasha S. Hanafi, Rasha M. El-Nashar, Hassan Y. Aboul-Enein

Analysis of water-soluble vitamins has been tremendously approached through the last decades. A multitude of HPLC methods have been reported with a variety of advantages/shortcomings, yet, the design space of HPLC analysis of these vitamins was not defined in any of these reports. As per the food and drug administration (FDA), implementing the quality by design approach for the analysis of commercially available mixtures is hypothesized to enhance the pharmaceutical industry via facilitating the process of analytical method development and approval. This work illustrates a multifactorial optimization of three measured plus seven calculated influential HPLC parameters on the analysis of a mixture containing seven common water-soluble vitamins (B1, B2, B6, B12, C, PABA, and PP). These three measured parameters are gradient time, temperature, and ternary eluent composition (B1/B2) and the seven calculated parameters are flow rate, column length, column internal diameter, dwell volume, extracolumn volume, %B (start), and %B (end). The design is based on 12 experiments in which, examining of the multifactorial effects of these 3 + 7 parameters on the critical resolution and selectivity, was carried out by systematical variation of all these parameters simultaneously. The 12 basic runs were based on two different gradient time each at two different temperatures, repeated at three different ternary eluent compositions (methanol or acetonitrile or a mixture of both). Multidimensional robust regions of high critical Rs were defined and graphically verified. The optimum method was selected based on the best resolution separation in the shortest run time for a synthetic mixture, followed by application on two pharmaceutical preparations available in the market. The predicted retention times of all peaks were found to be in good match with the virtual ones. In conclusion, the presented report offers an accurate determination of the design space for critical resolution in the analysis of water-soluble vitamins by HPLC, which would help the regulatory authorities to judge the validity of presented analytical methods for approval.

Journal of Pharmaceutical and Biomedical Analysis · 2013

Exploring better column selectivity choices in ultra-high performance liquid chromatography using Quality by Design principles

Róbert Kormány, Imre Molnár, Hans-Jürgen Rieger

An older method for amlodipine was reworked with the goal to reduce the analysis time of 60min below 6min. To select the best column for short and robust analysis, 9 different UHPLC column chemistries were investigated using 3-dimensional resolution spaces based on 12 experiments using modelling software. The main variables used were gradient time (tG), temperature (T) and the pH of eluent A. The best critical resolution was calculated and located in a 3-dimensional space in an automated fashion and the corresponding best experiments were carried out. The work (9×12=108 runs) was finished with an UHPLC instrument in less than 24h. The comparison between predictions and real experiments showed an excellent correlation with differences typically less than 0.04min (<3s) in average, although the set points were located at quite different conditions on gradient times, pH's and temperatures for the individual columns. All columns could perform the required baseline separation at their individual best working points with satisfactory results.

Food Analytical Methods · 2013

A High-Performance Liquid Chromatographic Method for Simultaneous Determination of 21 Free Amino Acids in Tea

Ming Zhao, Yan Ma, Lei-li Dai, Dong-lian Zhang, Jia-hua Li, Wen-xia Yuan, Ya-li Li, Hong-jie Zhou

Free amino acids are closely related to the savory taste and beneficial effects of tea, and high-performance liquid chromatography (HPLC) is the most widespread analytical approach for simultaneous determination of free amino acids in tea. However, the reported HPLC methods have drawbacks such as long run times, low resolution, or poor efficiency. In this study, a special amino acid analysis column was used to separate and verify 21 amino acids including l-theanine, the predominant amino acid in tea. The mobile phases, including the sodium acetate and acetic acid concentration in buffer B, and the pH and concentration of sodium acetate in buffer A were optimized. The elution gradients were optimized using DryLab 2000 Plus software. In this way, an online o-phthaldialdehyde precolumn derivatization HPLC-fluorescence detection method was developed for simultaneous determination of 21 amino acids. Comparison to other HPLC methods for simultaneous determination of free amino acids in tea showed that our method is easy (automated derivatization), quick (30 min), inexpensive, and green (using a minimum of solution). It has good resolution (≥1.8) and high selectivity (interpark time ≥ 0.5 min). Free amino acids in six tea samples were analyzed. This work provides an HPLC method to simultaneously measure 21 amino acids in tea and potential in other food products.

Chromatography Today · 2013

Chromatography Modelling in High Performance Liquid Chromatography Method Development

Imre Molnár, Róbert Kormány

This article discusses the development of chromatography modelling of the last 30 years from the first software package for calculating resolution and capacity factors to the visual modelling of chromatograms for testing peak movements with altering elution conditions. Different approaches are discussed, such as retention modelling based on measurements, others based on molecular structure or on statistical considerations. The state-of-the-art will be demonstrated with a few applications of industrial importance.

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.

Journal of Chromatography A · 2013

Optimizing selectivity during reversed-phase high performance liquid chromatography method development: Prioritizing experimental conditions

Lloyd R. Snyder, John W. Dolan

Several different conditions can be varied to improve selectivity for reversed-phase chromatography (RPC). A reexamination of literature data suggests that changes in selectivity due to a change of column or mobile phase pH are largely replicated by changes in temperature or mobile phase composition (concentrations of acetonitrile and/or methanol). This suggests a reconsideration of the role of mobile phase pH and the column during method development.

Combinatorial Chemistry & High Throughput Screening · 2012

Influence of LC retention data on antitumor acridinones' classification evaluated by factor analysis method

Marcin Koba, Tomasz Baczek, Tomasz Ciesielski

The application of factor analysis (FA) method in classification of the antitumor acridinones based on high-performance liquid chromatography (HPLC) retention data and calculated parameters of lipophilicity as well as some nonempirical structural parameters was studied. First, a group of 19 acridinone (imidazoacridinone and triazoloacridinone) derivatives was chromatographed in six RP-HPLC systems, and the values of their HPLC retention data as retention' times determined in both 10 min and 30 min gradient times were obtained as well as log kw (retention factor log k extrapolated to 0% organic modifier) parameters using DryLab program were calculated. Additionally, molecular modeling studies were performed based on the structural formula of considered acridinones and structural descriptors were derived as well as log P parameters using some commonly available software were calculated and subsequently used. A matrix of 19 x 32 HPLC data together with log P data and molecular properties parameters was subjected to factor analysis and led to extract three main factors with eigenvalues higher than 1. The first principal component (factor 1) accounted for, by 80.87% of the variance in data, the second principal component (factor 2) explained 7.77% and the third principal component (factor 3) was responsible by 4.46% of data variance. The total data variance was at the level 93.09% and was explained by the first three principal components. Moreover, one of the most significant influences on the values of factor 1 and factor 2 possessed HPLC retention data and calculated parameters describing lipophilicity, respectively. More importantly, distribution of individual drugs on the plane determined by two principal components produced patterns in good agreement with their chemical structures as well as with their antitumor activity.

Chromatographia · 2012

Enhancing the Quality of Separation in One-Dimensional Peptide Mapping Using Mathematical Transformation

Róbert Berky, Szabolcs Fekete, Jenő Fekete

In this study, some practical examples are presented that show the quality of separations using very efficient columns packed with the latest generation of core shell sub-3 μm and fully porous sub-2 μm particles in one-dimensional peptide separations. This paper shows an approach for the analysis of proteins, such as high-resolution separations, and a data transformation process to improve peak recognition and analysis. Applying power functions on raw chromatographic data can be a neat tool in the field of biosimilar analysis, especially in comparability studies regarding the quality (primary structure) of proteins. Based on the results presented here, it can be stated that the use of power functions is beneficial for the comparison of chromatograms when peak areas are considered but has no effect when using peak heights. In this study, the new Acquity CSH columns (C18 and phenyl-hexyl) and the core–shell type wide pore Ascentis Express Peptide ES C18 material were applied with great success in peptide mapping. Finally, using phenyl-hexyl stationary phase in peptide separation seems to be a good alternative to the generally applied C18 or C4 phases.

Journal of Chromatography A · 2012

Fast high performance liquid chromatography separations for proteomic applications using Fused-Core® silica particles

Stephanie A. Schuster, Barry E. Boyes, Brian M. Wagner, Joseph J. Kirkland

The separation range of superficially porous particles (Fused-Core®) has been extended by design of particles with 160Å pores. These particles show superior kinetics (lower resistance to mass transfer), allowing fast separations of peptides and small proteins (molecular weights of <15,000). The high efficiency and relatively low back pressure of these 2.7μm Fused-Core particles has been maintained so that separations can be performed with conventional HPLC instruments. Longer columns can be used for higher resolution of complex mixtures of peptides, such as proteolytic digests. Highly reproducible separations of peptides at elevated temperatures with low pH mobile phases are maintained as a result of a stable bonded stationary phase. The utility of such highly stable materials is exemplified by separations of problematic amyloid peptides at low pH (TFA mobile phase) at an operational temperature of 100°C. To address the issue of poor peptide peak shape in formic acid-containing mobile phases we show that the addition of 10–20mM ammonium formate improves peak shape, retention and load tolerance of peptides. Use of the Fused-Core particle materials for separations of synthetic peptides and tryptic digests yields peak capacities that are comparable to those obtained using columns packed with sub-2-μm particles, but with less than one-half of the operating back pressure. A peak capacity of 530 was obtained in 150min on coupled columns of HALO Peptide ES-C18 with a combined length of 250mm.

Journal of Pharmaceutical and Biomedical Analysis · 2012

Analysis of recombinant monoclonal antibodies by RPLC: Toward a generic method development approach

Szabolcs Fekete, Serge Rudaz, Jenő Fekete, Davy Guillarme

Monoclonal antibodies (mAbs) are an emerging class of therapeutic agents that have recently gained importance. To attain acceptable kinetic performance with mAbs in reversed phase liquid chromatography, there is a need to work with the last generation of wide-pore sub-2μm fully porous or core–shell particles stationary phases. In addition, temperature in the range 60–90°C was found to be mandatory to limit adsorption phenomenon of mAbs and their fragments. A generic method development strategy was proposed to account for the selectivity, efficiency, recovery, and the possible thermal degradation. This study also demonstrated that the gradient steepness and temperature cannot be optimized using van’t Hoff type linear models. Similarly, the common linear solvent strength model also generated some error in predicting the retention times. In contrast, when quadratic models were employed, the prediction accuracy of retention times was found to be excellent (relative error between 0.5 and 1%) using a reasonable number of experiments (9 or 6 experiments for optimization of gradient time and temperature, which requires between 6 and 8h). Two separations of mAbs fragments were performed to demonstrate the reliability of the quadratic approach.

Journal of Chromatography A · 2012

A general strategy for performing temperature-programming in high performance liquid chromatography—Further improvements in the accuracy of retention time predictions of segmented temperature gradients

Steffen Wiese, Thorsten Teutenberg, Torsten C. Schmidt

In the present work it is shown that the linear elution strength (LES) model which was adapted from temperature-programming gas chromatography (GC) can also be employed for systematic method development in high-temperature liquid chromatography (HT-HPLC). The ability to predict isothermal retention times based on temperature-gradient as well as isothermal input data was investigated. For a small temperature interval of ΔT=40 °C, both approaches result in very similar predictions. Average relative errors of predicted retention times of 2.7% and 1.9% were observed for simulations based on isothermal and temperature-gradient measurements, respectively. Concurrently, it was investigated whether the accuracy of retention time predictions of segmented temperature gradients can be further improved by temperature dependent calculation of the parameter ST of the LES relationship. It was found that the accuracy of retention time predictions of multi-step temperature gradients can be improved to around 1.5%, if ST was also calculated temperature dependent. The adjusted experimental design making use of four temperature-gradient measurements was applied for systematic method development of selected food additives by high-temperature liquid chromatography. Method development was performed within a temperature interval from 40°C to 180°C using water as mobile phase. Two separation methods were established where selected food additives were baseline separated. In addition, a good agreement between simulation and experiment was observed, because an average relative error of predicted retention times of complex segmented temperature gradients less than 5% was observed. Finally, a schedule of recommendations to assist the practitioner during systematic method development in high-temperature liquid chromatography was established.

Open Chemistry · 2012

Determination of lipophilicity for antitumor acridinone derivatives supported by gradient high-performance liquid chromatography method

Marcin Koba, Mariusz Belka, Tomasz Ciesielski, Tomasz Bączek

The lipophilicity values of selected acridinone (imidazoacridinone and triazoloacridinone) derivatives were measured by gradient reversed-phase high-performance liquid chromatography (RP-HPLC) using a C18 stationary phase with a water/acetonitrile mixture as a mobile phase. The retention times obtained served as input data and appropriate log kw values (i.e., the retention factor log kw extrapolated to 0% organic modifier) as an alternative to log P were calculated using the DryLab program. The relationships between the lipophilicity (log kw) and the chemical structure of the studied compounds, as well as correlation between experimentally determined lipophilicities (log kw) and log P data calculated using some commonly available software, are discussed.

Journal of Chromatography A · 2012

Quality by Design: Multidimensional exploration of the design space in high performance liquid chromatography method development for better robustness before validation

Kate E. Monks, Imre Molnár, Hans-Jürgen Rieger, Botond Bogáti, E. Szabó

Robust HPLC separations lead to fewer analysis failures and better method transfer as well as providing an assurance of quality. This work presents the systematic development of an optimal, robust, fast UHPLC method for the simultaneous assay of two APIs of an eye drop sample and their impurities, in accordance with Quality by Design principles. Chromatography software is employed to effectively generate design spaces (Method Operable Design Regions), which are subsequently employed to determine the final method conditions and to evaluate robustness prior to validation.

Journal of Pharmaceutical and Biomedical Analysis · 2012

New trends in reversed-phase liquid chromatographic separations of therapeutic peptides and proteins: theory and applications

Szabolcs Fekete, Jean-Luc Veuthey, Davy Guillarme

In the pharmaceutical field, there is considerable interest in the use of peptides and proteins for therapeutic purposes. There are various ways to characterize such complex samples, but during the last few years, a significant number of technological developments have been brought to the field of RPLC and RPLC-MS. Thus, the present review focuses first on the basics of RPLC for peptides and proteins, including the inherent problems, some possible solutions and some directions for developing a new RPLC method that is dedicated to biomolecules. Then the latest advances in RPLC, such as wide-pore core-shell particles, fully porous sub-2 μm particles, organic monoliths, porous layer open tubular columns and elevated temperature, are described and critically discussed in terms of both kinetic efficiency and selectivity. Numerous applications with real samples are presented that confirm the relevance of these different strategies. Finally, one of the key advantages of RPLC for peptides and proteins over other historical approaches is its inherent compatibility with MS using both MALDI and ESI sources.

The Column · 2012

Practical Application of Quality by Design Principles to The Development of an HPLC Assay Method for an API and Impurities

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

A method for the assay of an active pharmaceutical ingredient (API) and five known and unknown impurities was developed in accordance with Quality by Design (QbD) principles. Highly influential separation parameters were simultaneously and systematically studied so that the quality of the HPLC method could be understood, controlled and ensured. Consequently, during routine analysis out of specification (OOS) results can be corrected more effectively.

Decades of chromatography research done with DryLab®.

Determination of alcohols in essential oils by liquid chromatography with ultraviolet detection after chromogenic derivatization

Using an innovative Quality-by-Design approach for development of a stability indicating UHPLC method for ebastine in the API and pharmaceutical formulations

Comparison of supercritical fluid chromatography and reverse phase liquid chromatography for the impurity profiling of the antiretroviral drugs lamivudine/BMS-986001/efavirenz in a combination tablet

Intergroup cross-comparison for the evaluation of data-interchangeability from various chromatographic tests

Application of Quality by Design Principles to a Pharmaceutical Sample Using UHPLC Method Development with Modeling Technologies

Determination of the design space of the HPLC analysis of water-soluble vitamins

Exploring better column selectivity choices in ultra-high performance liquid chromatography using Quality by Design principles

A High-Performance Liquid Chromatographic Method for Simultaneous Determination of 21 Free Amino Acids in Tea

Chromatography Modelling in High Performance Liquid Chromatography Method Development

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

Optimizing selectivity during reversed-phase high performance liquid chromatography method development: Prioritizing experimental conditions

Influence of LC retention data on antitumor acridinones' classification evaluated by factor analysis method

Enhancing the Quality of Separation in One-Dimensional Peptide Mapping Using Mathematical Transformation

Fast high performance liquid chromatography separations for proteomic applications using Fused-Core® silica particles

Analysis of recombinant monoclonal antibodies by RPLC: Toward a generic method development approach

A general strategy for performing temperature-programming in high performance liquid chromatography—Further improvements in the accuracy of retention time predictions of segmented temperature gradients

Determination of lipophilicity for antitumor acridinone derivatives supported by gradient high-performance liquid chromatography method

Quality by Design: Multidimensional exploration of the design space in high performance liquid chromatography method development for better robustness before validation

New trends in reversed-phase liquid chromatographic separations of therapeutic peptides and proteins: theory and applications

Practical Application of Quality by Design Principles to The Development of an HPLC Assay Method for an API and Impurities