The hydrophobic subtraction model (HSM) combined with quantitative structure‐retention relationsh... more The hydrophobic subtraction model (HSM) combined with quantitative structure‐retention relationships (QSRR) methodology was utilized to predict retention times in reversed‐phase liquid chromatography (RPLC). A selection of new analytes and new RPLC columns that had never been used in the QSRR modeling process were used to verify the proposed approach. This work is designed to facilitate early prediction of co‐elution of analytes in pharmaceutical drug discovery applications where it is advantageous to predict whether impurities might be co‐eluted with the active drug component. The QSRR models were constructed through partial least squares regression combined with a genetic algorithm (GA‐PLS) which was employed as a feature selection method to choose the most informative molecular descriptors calculated using VolSurf+ software. The analyte hydrophobicity coefficient of the HSM was predicted for subsequent calculation of retention. Clustering approaches based on the local compound ty...
With an enormous growth in the application of hydrophilic interaction liquid chromatography (HILI... more With an enormous growth in the application of hydrophilic interaction liquid chromatography (HILIC), there has also been significant progress in HILIC method development. HILIC is a chromatographic method that utilises hydro-organic mobile phases with a high organic content, and a hydrophilic stationary phase. It has been applied predominantly in the determination of small polar compounds. Theoretical studies in computer-aided modelling tools, most importantly the predictive, quantitative structure retention relationship (QSRR) modelling methods, have attracted the attention of researchers and these approaches greatly assist the method development process. This review focuses on the application of computer-aided modelling tools in understanding the retention mechanism, the classification of HILIC stationary phases, prediction of retention times in HILIC systems, optimisation of chromatographic conditions, and description of the interaction effects of the chromatographic factors in H...
Journal of pharmaceutical and biomedical analysis, Jan 27, 2016
Stability studies of pharmaceutical drug products and pharmaceutical active substances are import... more Stability studies of pharmaceutical drug products and pharmaceutical active substances are important to research and development in order to fully understand and maintain product quality and safety throughout its shelf-life. Oxidative forced degradation studies are among the different types of stability studies performed by the pharmaceutical industry in order to understand the intrinsic stability of drug molecules. We have been comparing the use of electrochemistry as an alternative oxidative forced degradation method to traditional forced degradation and accelerated stability studies. Using the electrochemical degradation approach the substrate oxidation takes place in a commercially available electrochemical cell and the effluent of the cell can be either a) directly infused into the mass spectrometer or b) injected in a chromatographic column for separation of the different products formed prior to the mass spectrometry analysis. To enable the study of large numbers of different...
Porting is a powerful methodology to recalibrate an existing database of ion chromatography (IC) ... more Porting is a powerful methodology to recalibrate an existing database of ion chromatography (IC) retention times by reflecting the changes of column behavior resulting from either batch-to-batch variability in the production of the column or the manufacture of new versions of a column. This approach has been employed to update extensive databases of retention data of inorganic and organic anions forming part of the "Virtual Column" software marketed by Thermo Fisher Scientific, which is the only available commercial optimization tool for IC separation. The current porting process is accomplished by performing three isocratic separations with two representative analyte ions in order to derive a porting equation which expresses the relationship between old and new data. Although the accuracy of retention prediction is generally enhanced on new columns, errors were observed on some columns. In this work, the porting methodology was modified in order to address this issue, whe...
The relative performance of six multivariate data analysis methods derived from or combined with ... more The relative performance of six multivariate data analysis methods derived from or combined with partial least squares (PLS) has been compared in the context of quantitative structure-retention relationships (QSRR). These methods include, GA (genetic algorithm)-PLS, Monte Carlo uninformative variable elimination (MC-UVE), competitive adaptive reweighted sampling (CARS), iteratively retaining informative variables (IRIV), variable iterative space shrinkage approach (VISSA) and PLS with automated backward selection of predictors (autoPLS). A set of 825 molecular descriptors was computed for 86 suspected sports doping compounds and used for predicting their gradient retention times in reversed-phase liquid chromatography (RPLC). The correlation between molecular descriptors selected by each technique and the retention time was established using the PLS method. All models derived from a selected subset of descriptors outperformed the reference PLS model derived from all descriptors, wit...
Journal of pharmaceutical and biomedical analysis, Jan 13, 2015
The aim of this study was to evaluate the use of electrochemistry to generate oxidative degradati... more The aim of this study was to evaluate the use of electrochemistry to generate oxidative degradation products of a model pharmaceutical compound. The compound was oxidized at different potentials using an electrochemical flow-cell fitted with a glassy carbon working electrode, a Pd/H2 reference electrode and a titanium auxiliary electrode. The oxidative products formed were identified and structurally characterized by LC-ESI-MS/MS using a high resolution Q-TOF mass spectrometer. Results from electrochemical oxidation using electrolytes of different pH were compared to those from chemical oxidation and from accelerated stability studies. Additionally, oxidative degradation products predicted using an in silico commercially available software were compared to those obtained from the various experimental methods. The electrochemical approach proved to be useful as an oxidative stress test as all of the final oxidation products observed under accelerated stability studies could be genera...
Over the past decades, several in vitro methods have been tested for their ability to predict eit... more Over the past decades, several in vitro methods have been tested for their ability to predict either human intestinal absorption (HIA) or penetration across the blood-brain barrier (BBB) of drugs. Micellar liquid chromatography (MLC) has been a successful approach for retention time measurements of drugs to establish models together with other molecular descriptors. Thus far, MLC approaches have only made use of commercial surfactants such as sodium dodecyl sulfate (SDS) and polyoxyethylene (23) lauryl ether (Brij35), which are not representative for the phospholipids present in human membranes. Miltefosine, a phosphocholine-based lipid, is presented here as an alternative surfactant for MLC measurements. By using the obtained retention factors and several computed descriptors for a set of 48 compounds, two models were constructed: one for the prediction of HIA and another for the prediction of penetration across the BBB expressed as log BB. All data were correlated to experimental HIA and log BB values, and the performance of the models was evaluated. Log BB prediction performed better than HIA prediction, although HIA prediction was also improved a lot (from 0.5530 to 0.7175) compared to in silico predicted HIA values.
Abstract The primary focus of separation scientists supporting pharmaceutical drug development is... more Abstract The primary focus of separation scientists supporting pharmaceutical drug development is to provide evidence of safety of medicines administered to patients and volunteers during clinical trials. This critical objective is achieved through application of various forms of state-of-the-art separation science techniques, often combined with spectroscopic detection techniques. The role of separation science, which plays a pivotal role in all phases of pharmaceutical drug development, is extensively described in the introductory part of this contribution. The early stages of pharmaceutical drug development typically require chromatographic techniques that provide very high resolution. This is essential as, at this stage of development, a relatively large number of process-related impurities, synthetic intermediates, and degradation products must be separated to characterize starting materials and products of chemical synthesis. In the first part of this chapter, we focus on multiple ways of enhancing chromatographic resolution for the purposes of satisfying these early development demands. In the later stages of the drug development process, when the manufacturing processes are being qualified, the emphasis shifts from resolution to speed, ruggedness, and robustness. The second part of this chapter provides an overview of useful tools and techniques that may be applied in such a setting. In the final part of this chapter, we ocus on novel trends in chromatographic method development related to the analytical quality by design initiative (AQbD).
... This unique beer type was derived from the action of wild yeasts present in the ambient air i... more ... This unique beer type was derived from the action of wild yeasts present in the ambient air in the valley of the river Senne, just south trends in analytical chemistry ... Ho scnsitizcr HO 0 0 OH 0 OH + Ho 0 .,.OOH O 1 OH Snor0ulnm; IU compound, 13 46 79 7 1 R=CHZCH(CH3)i:1,4,7 ...
Stationary phase optimized selectivity liquid chromatography (SOSLC) is a promising technique to ... more Stationary phase optimized selectivity liquid chromatography (SOSLC) is a promising technique to optimize the selectivity of a given separation. By combination of different stationary phases, SOSLC offers excellent possibilities for method development under both isocratic and gradient conditions. The so far available commercial SOSLC protocol utilizes dedicated column cartridges and corresponding cartridge holders to build up the combined column of different stationary phases. The present work is aimed at developing and extending the gradient SOSLC approach towards coupling conventional columns. Generic tubing was used to connect short commercially available LC columns. Fast and base-line separation of a mixture of 12 compounds containing phenones, benzoic acids and hydroxybenzoates under both isocratic and linear gradient conditions was selected to demonstrate the potential of SOSLC. The influence of the connecting tubing on the deviation of predictions is also discussed.
A low thermal mass column oven was used for fast capillary GC analysis (high throughput) of resid... more A low thermal mass column oven was used for fast capillary GC analysis (high throughput) of residual solvents in pharmaceutical products. A dedicated capillary column, 20 m L x 180 microm ID x 1 microm DB-624 was programmed from 35 degrees C (30 s) to 150 degrees C at 100 degrees C/min and to 250 degrees C (30 s) at 200 degrees C/min, resulting in a total GC cycle time of less than 4 min. Complete separation of a target 20-component mixture was achieved, while method performance in terms of repeatability, sensitivity, and linearity was maintained in comparison to the generic method currently applied in our laboratories.
The coupling of RP‐LC to electron capture detection (ECDNi63) is described. To reduce the amount ... more The coupling of RP‐LC to electron capture detection (ECDNi63) is described. To reduce the amount of mobile phase entering into the detector, interfacing was performed via a Scott‐type spray chamber. The performance of RP‐LC/ECDNi63 was evaluated for pharmaceutical analysis and the results show that the system is able to work in a routine environment using columns with 2 mm id and common amounts of the organic modifiers methanol or ACN in the mobile phase. Because of the high sensitivity and selectivity toward electrophilic compounds, the use of this detector opens possibilities for the analysis of impurities down to the 0.05% level of active pharmaceutical ingredients (API).
The hydrophobic subtraction model (HSM) combined with quantitative structure‐retention relationsh... more The hydrophobic subtraction model (HSM) combined with quantitative structure‐retention relationships (QSRR) methodology was utilized to predict retention times in reversed‐phase liquid chromatography (RPLC). A selection of new analytes and new RPLC columns that had never been used in the QSRR modeling process were used to verify the proposed approach. This work is designed to facilitate early prediction of co‐elution of analytes in pharmaceutical drug discovery applications where it is advantageous to predict whether impurities might be co‐eluted with the active drug component. The QSRR models were constructed through partial least squares regression combined with a genetic algorithm (GA‐PLS) which was employed as a feature selection method to choose the most informative molecular descriptors calculated using VolSurf+ software. The analyte hydrophobicity coefficient of the HSM was predicted for subsequent calculation of retention. Clustering approaches based on the local compound ty...
With an enormous growth in the application of hydrophilic interaction liquid chromatography (HILI... more With an enormous growth in the application of hydrophilic interaction liquid chromatography (HILIC), there has also been significant progress in HILIC method development. HILIC is a chromatographic method that utilises hydro-organic mobile phases with a high organic content, and a hydrophilic stationary phase. It has been applied predominantly in the determination of small polar compounds. Theoretical studies in computer-aided modelling tools, most importantly the predictive, quantitative structure retention relationship (QSRR) modelling methods, have attracted the attention of researchers and these approaches greatly assist the method development process. This review focuses on the application of computer-aided modelling tools in understanding the retention mechanism, the classification of HILIC stationary phases, prediction of retention times in HILIC systems, optimisation of chromatographic conditions, and description of the interaction effects of the chromatographic factors in H...
Journal of pharmaceutical and biomedical analysis, Jan 27, 2016
Stability studies of pharmaceutical drug products and pharmaceutical active substances are import... more Stability studies of pharmaceutical drug products and pharmaceutical active substances are important to research and development in order to fully understand and maintain product quality and safety throughout its shelf-life. Oxidative forced degradation studies are among the different types of stability studies performed by the pharmaceutical industry in order to understand the intrinsic stability of drug molecules. We have been comparing the use of electrochemistry as an alternative oxidative forced degradation method to traditional forced degradation and accelerated stability studies. Using the electrochemical degradation approach the substrate oxidation takes place in a commercially available electrochemical cell and the effluent of the cell can be either a) directly infused into the mass spectrometer or b) injected in a chromatographic column for separation of the different products formed prior to the mass spectrometry analysis. To enable the study of large numbers of different...
Porting is a powerful methodology to recalibrate an existing database of ion chromatography (IC) ... more Porting is a powerful methodology to recalibrate an existing database of ion chromatography (IC) retention times by reflecting the changes of column behavior resulting from either batch-to-batch variability in the production of the column or the manufacture of new versions of a column. This approach has been employed to update extensive databases of retention data of inorganic and organic anions forming part of the "Virtual Column" software marketed by Thermo Fisher Scientific, which is the only available commercial optimization tool for IC separation. The current porting process is accomplished by performing three isocratic separations with two representative analyte ions in order to derive a porting equation which expresses the relationship between old and new data. Although the accuracy of retention prediction is generally enhanced on new columns, errors were observed on some columns. In this work, the porting methodology was modified in order to address this issue, whe...
The relative performance of six multivariate data analysis methods derived from or combined with ... more The relative performance of six multivariate data analysis methods derived from or combined with partial least squares (PLS) has been compared in the context of quantitative structure-retention relationships (QSRR). These methods include, GA (genetic algorithm)-PLS, Monte Carlo uninformative variable elimination (MC-UVE), competitive adaptive reweighted sampling (CARS), iteratively retaining informative variables (IRIV), variable iterative space shrinkage approach (VISSA) and PLS with automated backward selection of predictors (autoPLS). A set of 825 molecular descriptors was computed for 86 suspected sports doping compounds and used for predicting their gradient retention times in reversed-phase liquid chromatography (RPLC). The correlation between molecular descriptors selected by each technique and the retention time was established using the PLS method. All models derived from a selected subset of descriptors outperformed the reference PLS model derived from all descriptors, wit...
Journal of pharmaceutical and biomedical analysis, Jan 13, 2015
The aim of this study was to evaluate the use of electrochemistry to generate oxidative degradati... more The aim of this study was to evaluate the use of electrochemistry to generate oxidative degradation products of a model pharmaceutical compound. The compound was oxidized at different potentials using an electrochemical flow-cell fitted with a glassy carbon working electrode, a Pd/H2 reference electrode and a titanium auxiliary electrode. The oxidative products formed were identified and structurally characterized by LC-ESI-MS/MS using a high resolution Q-TOF mass spectrometer. Results from electrochemical oxidation using electrolytes of different pH were compared to those from chemical oxidation and from accelerated stability studies. Additionally, oxidative degradation products predicted using an in silico commercially available software were compared to those obtained from the various experimental methods. The electrochemical approach proved to be useful as an oxidative stress test as all of the final oxidation products observed under accelerated stability studies could be genera...
Over the past decades, several in vitro methods have been tested for their ability to predict eit... more Over the past decades, several in vitro methods have been tested for their ability to predict either human intestinal absorption (HIA) or penetration across the blood-brain barrier (BBB) of drugs. Micellar liquid chromatography (MLC) has been a successful approach for retention time measurements of drugs to establish models together with other molecular descriptors. Thus far, MLC approaches have only made use of commercial surfactants such as sodium dodecyl sulfate (SDS) and polyoxyethylene (23) lauryl ether (Brij35), which are not representative for the phospholipids present in human membranes. Miltefosine, a phosphocholine-based lipid, is presented here as an alternative surfactant for MLC measurements. By using the obtained retention factors and several computed descriptors for a set of 48 compounds, two models were constructed: one for the prediction of HIA and another for the prediction of penetration across the BBB expressed as log BB. All data were correlated to experimental HIA and log BB values, and the performance of the models was evaluated. Log BB prediction performed better than HIA prediction, although HIA prediction was also improved a lot (from 0.5530 to 0.7175) compared to in silico predicted HIA values.
Abstract The primary focus of separation scientists supporting pharmaceutical drug development is... more Abstract The primary focus of separation scientists supporting pharmaceutical drug development is to provide evidence of safety of medicines administered to patients and volunteers during clinical trials. This critical objective is achieved through application of various forms of state-of-the-art separation science techniques, often combined with spectroscopic detection techniques. The role of separation science, which plays a pivotal role in all phases of pharmaceutical drug development, is extensively described in the introductory part of this contribution. The early stages of pharmaceutical drug development typically require chromatographic techniques that provide very high resolution. This is essential as, at this stage of development, a relatively large number of process-related impurities, synthetic intermediates, and degradation products must be separated to characterize starting materials and products of chemical synthesis. In the first part of this chapter, we focus on multiple ways of enhancing chromatographic resolution for the purposes of satisfying these early development demands. In the later stages of the drug development process, when the manufacturing processes are being qualified, the emphasis shifts from resolution to speed, ruggedness, and robustness. The second part of this chapter provides an overview of useful tools and techniques that may be applied in such a setting. In the final part of this chapter, we ocus on novel trends in chromatographic method development related to the analytical quality by design initiative (AQbD).
... This unique beer type was derived from the action of wild yeasts present in the ambient air i... more ... This unique beer type was derived from the action of wild yeasts present in the ambient air in the valley of the river Senne, just south trends in analytical chemistry ... Ho scnsitizcr HO 0 0 OH 0 OH + Ho 0 .,.OOH O 1 OH Snor0ulnm; IU compound, 13 46 79 7 1 R=CHZCH(CH3)i:1,4,7 ...
Stationary phase optimized selectivity liquid chromatography (SOSLC) is a promising technique to ... more Stationary phase optimized selectivity liquid chromatography (SOSLC) is a promising technique to optimize the selectivity of a given separation. By combination of different stationary phases, SOSLC offers excellent possibilities for method development under both isocratic and gradient conditions. The so far available commercial SOSLC protocol utilizes dedicated column cartridges and corresponding cartridge holders to build up the combined column of different stationary phases. The present work is aimed at developing and extending the gradient SOSLC approach towards coupling conventional columns. Generic tubing was used to connect short commercially available LC columns. Fast and base-line separation of a mixture of 12 compounds containing phenones, benzoic acids and hydroxybenzoates under both isocratic and linear gradient conditions was selected to demonstrate the potential of SOSLC. The influence of the connecting tubing on the deviation of predictions is also discussed.
A low thermal mass column oven was used for fast capillary GC analysis (high throughput) of resid... more A low thermal mass column oven was used for fast capillary GC analysis (high throughput) of residual solvents in pharmaceutical products. A dedicated capillary column, 20 m L x 180 microm ID x 1 microm DB-624 was programmed from 35 degrees C (30 s) to 150 degrees C at 100 degrees C/min and to 250 degrees C (30 s) at 200 degrees C/min, resulting in a total GC cycle time of less than 4 min. Complete separation of a target 20-component mixture was achieved, while method performance in terms of repeatability, sensitivity, and linearity was maintained in comparison to the generic method currently applied in our laboratories.
The coupling of RP‐LC to electron capture detection (ECDNi63) is described. To reduce the amount ... more The coupling of RP‐LC to electron capture detection (ECDNi63) is described. To reduce the amount of mobile phase entering into the detector, interfacing was performed via a Scott‐type spray chamber. The performance of RP‐LC/ECDNi63 was evaluated for pharmaceutical analysis and the results show that the system is able to work in a routine environment using columns with 2 mm id and common amounts of the organic modifiers methanol or ACN in the mobile phase. Because of the high sensitivity and selectivity toward electrophilic compounds, the use of this detector opens possibilities for the analysis of impurities down to the 0.05% level of active pharmaceutical ingredients (API).
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Papers by Roman Szucs