Biomedical subjects

Y Vander Heyden

Publications and source records attributed to Y Vander Heyden.

At least 19 recordsLinked to original sources

PubMed2003

Fast separations on monolithic silica columns: method transfer, robustness and column ageing for some case studies.

Six separation methods, developed on conventional silica high performance liquid chromatography (HPLC) columns were transferred to monolithic silica columns of 5 and 10 cm length. The transferred methods include the separation of an alkylbenzene mixture, the separations of drugs from their impurities (nimesulide, tetracycline, phenoxymethylpenicillin and erythromycin) and the separation of a green tea extract. The transfer of the first three methods was successful while for the latter three it was not. Increasing the flow rate up to 9 ml/min (where possible) inversely decreased the analysis time of the successfully transferred methods to 48 s (alkylbenzene mixture) 1.8 min (nimesulide mixture) and 3 min (tetracycline mixture) while still reasonable well separated peaks were obtained. The robustness and repeatability of the transferred and accelerated separations was found to be acceptable. Despite the use of flow rates up to 9 ml/min and frequent mobile phase changes with pH values varying from 3.5 to 7, the column performance was found to be rather constant and the column ageing to be minimal.

Chromatography, High Pressure Liquid↗

PubMed2003

Validation of an HPLC method on short columns to assay ketoconazole and formaldehyde in shampoo.

An HPLC method to determine simultaneously ketoconazole and formaldehyde in an anti-dandruff shampoo, originally developed on a long column, was transferred to two short columns with similar stationary phase properties, but with a length of at the most 30% of the initial one. Using the conventional column as reference, the fast HPLC methods on the short columns were validated. The validation characteristics consisted of selectivity, linearity range, precision (repeatability and time-different intermediate precision), bias and robustness. For the ketoconazole assay, linearity for peak area was found in the concentration range up to 0.20 mg/ml. For formaldehyde, two calibration ranges (0-10 x 10(-5) and 0-10 x 10(-4)%) were linear, both for peak area and height. The assays for both ketoconazole and formaldehyde in these ranges showed no bias and an acceptable precision, although the precision found with the short columns was slightly worse than with the long one. The robustness tests were performed applying a Plackett-Burman design. For the ketoconazole assay, 6 factors were examined in a 12 experiments design and for formaldehyde, 11 factors in 16 experiments. The methods were found to be robust. Despite the somewhat less good precision the transfer seems to be successful and the obtained assays on the short columns are applicable for fast routine analysis.

Antifungal Agents↗

PubMed2003

Classification and regression tree analysis for molecular descriptor selection and retention prediction in chromatographic quantitative structure-retention relationship studies.

The use of the classification and regression tree (CART) methodology was studied in a quantitative structure-retention relationship (QSRR) context on a data set consisting of the retentions of 83 structurally diverse drugs on a Unisphere PBD column, using isocratic elutions at pH 11.7. The response (dependent variable) in the tree models consisted of the predicted rention factor (log kw) of the solutes, while a set of 266 molecular descriptors was used as explanatory variables in the tree building. Molecular descriptors related to the hydrophobicity (log P and Hy) and the size (TPC) of the molecules were selected out of these 266 descriptors in order to describe and predict retention. Besides the above mentioned, CART was also able to select hydrogen-bonding and molecular complexity descriptors. Since these variables are expected from QSRR knowledge, it demonstrates the potential of CART as a methodology to understand retention in chromatographic systems. The potential of CART to predict retention and thus occasionally to select an appropriate system for a given mixture was also evaluated. Reasonably good prediction, i.e. only 9% serious misclassification, was observed. Moreover, some of the misclassifications probably are inherent to the data set applied.

Chromatography↗

PubMed2003

Determining orthogonal chromatographic systems prior to the development of methods to characterise impurities in drug substances.

To define starting conditions for the development of methods to separate impurities from the active substance and from each other in drugs with an unknown impurity profile, the parallel application of generic orthogonal chromatographic systems could be useful. The possibilities to define orthogonal chromatographic systems were examined by calculation of the correlation coefficients between retention factors k for a set of 68 drugs on 11 systems, by visual evaluation of the selectivity differences, by using principal component analysis, by drawing color maps and evaluating dendrograms. A zirconia-based stationary phase coated with a polybutadiene (PBD) polymer and three silica-based phases (base-deactivated, polar-embedded and monolithic) were used. Besides the stationary phase, the influence of pH and of organic modifier, on the selectivity of a system were evaluated. The dendrograms of hierarchical clusters were found good aids to assess orthogonality of chromatographic systems. The PBD-zirconia phase/methanol/pH 2.5 system is found most orthogonal towards several silica-based systems, e.g. a base-deactivated C16 -amide silica/methanol/pH 2.5 system. The orthogonality was validated using cross-validation, and two other validation sets, i.e. a set of non-ionizable solutes and a mixture of a drug and its impurities.

Chromatography, High Pressure Liquid↗

PubMed2003

Chemometric comparison of recent chromatographic and electrophoretic methods in a quantitative structure-retention and retention-activity relationship context.

The retention characteristics of 21 basic pharmaceutical substances with a considerable difference in hydrophobicity (octanol-water partition coefficients, log P, between -0.026 and 6.45) are considered on an immobilized artificial membrane column, with a micellar liquid chromatography and a micellar electrokinetic capillary chromatography method. Utilising principal component analysis (PCA), it is seen that although the main retention principle is the same, the above methods as well as more classical RP-HPLC methods vary in secondary retention mechanisms. Combining the results of different methods a differentiation of the substances into their pharmacological families can be seen with PCA. The high correlations of the retention characteristics with log P and a biological parameter seem little affected by the method used.

Chromatography, High Pressure Liquid↗

PubMed2003

Contribution of the polymer standards' polydispersity to the observed band broadening in size-exclusion chromatography.

The contribution of the polydispersity of polymer standards to the observed band broadening in size-exclusion chromatography was evaluated. Initially, theoretical predictions based on an equation by Knox et al. were found to overestimate this contribution, greatly due to the fact that the polydispersity values specified by the manufacturers are upper limits and therefore too high to be applied in this context. An improved estimate of the polydispersity values was obtained from the size-exclusion chromatography results and these new values were used to reassess the polydispersity contribution to band broadening. For two of three columns tested the best molar-mass-distribution parameters, i.e. those the least affected by extra-column and intra-column band broadening effects, can be obtained for polymers with a molar mass in the effective range of the given column and at rather low mobile-phase flow rates. At those conditions, for low-molar-mass polymers, the estimated polydispersity index values approach the theoretical ones derived from a Poisson distribution.

Chromatography, Gel↗

PubMed2003

[Tests for robustness of biomedical and pharmaceutical analytic methods].

In biomedical and pharmaceutical analysis, especially in the analyses executed in the pharmaceutical industry, the quality of the results obtained is strictly evaluated and controlled. Therefore, newly developed methods of analysis are subjected to a strict and vast method validation. One of the validation criteria studied is the determination of the robustness of the method. This is done by means of a robustness test. In this manuscript the different steps required to set up and interpret a robustness test are discussed and illustrated with a number of examples.

Chemistry Techniques, Analytical↗

PubMed2002

Optimisation by experimental design of a capillary electrophoretic method for the separation of several inhibitors of angiotensin-converting enzyme using alkylsulphonates.

A statistical experimental design was used to optimise a capillary electrophoretic separation method for eight inhibitors of the angiotensin-converting enzyme: enalapril, lisinopril, quinapril, fosinopril, perindopril, ramipril, benazepril, and cilazapril. Because a free solution capillary electrophoresis system did not achieve a complete separation of these eight compounds in one run, the usefulness of alkylsulphonates as ion-pairing agents was investigated. After preliminary investigations to determine the experimental domain and the most important factors, a three-level full-factorial design was applied to study the impact of the pH and the molarity of the ion-pairing agent on the separation. Improved separations were obtained suggesting a favourable effect of ion-pairing interactions between analytes and the additive; however, it remained impossible to separate them all in one run. A combination of two systems was still necessary for the selective identification of these structurally-related substances.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2002

Screening approach for chiral separation of pharmaceuticals part II. Reversed-phase liquid chromatography.

A screening strategy for the rapid separation of drug enantiomers by reversed-phase liquid chromatography was developed using three cellulose/amylose stationary phases. The key point to achieve enantioselectivity is the control of the compound ionisation. Only two mobile phases, i.e. an acidic phosphate buffer (pH 2.0) containing a chaotropic salt (KPF6) and a borate buffer (pH 9.0) mixed with acetonitrile, are used in the proposed strategy. This strategy was successfully applied to a set of 37 diverse chiral pharmaceuticals. Satisfactory enantioselectivity was achieved for 89% of them.

Acids↗

PubMed2002

Screening and optimisation of an ELISA method for the quantitative detection of enterovirus specific RT-PCR products by means of a two-level experimental design.

In a previous paper, optimal reaction conditions were determined for the RT-PCR part of a quantitative enterovirus specific RT-PCR ELISA method (J. Pharm. Biomed. Anal., 25 (2001) 131-142). In order to obtain a detection limit as low as possible, the ELISA part of the procedure was optimised as well. This was done by investigating the influence of seven factors at three levels in a multivariate approach. A reflected two-level screening design, derived from a Plackett-Burman design, was used. Optimal reaction conditions were established by calculation and by evaluation of the effects of the factors on the measured absorbance of the ELISA detection. Under these conditions, the linear range and detection limit of the test were determined and compared with the ELISA conditions before optimisation. The optimised RT-PCR ELISA will be used to study a possible longitudinal relationship between enteroviruses and the development of multiple sclerosis and juvenile diabetes.

Enterovirus↗

PubMed2002

Evaluation of size-exclusion chromatography and size-exclusion electrochromatography calibration curves.

Size-exclusion chromatography (SEC) and size-exclusion electrochromatography (SEEC) are chromatographic techniques used to determine molecular mass (weight) distributions (MWD) of polymers. One important step in the data treatment to derive MWD parameters is the modelling of the calibration curves. The calibration curves applied in SEC and SEEC are generally not linear. In this study the modelling of calibration curves is being examined. Different polynomial models have been evaluated and compared, not only for model fit but also for their predictive properties. It was found that sometimes a straight line and sometimes a third-order polynomial model were best. The best model across the effective range (also called linear range) is not always found to be a straight line. The SEEC curves were found to have considerably higher prediction errors than the SEC ones. Reduction of the number of calibration standards to five or six did not greatly affect the predictive properties of the calibration curves, neither in SEC nor in SEEC.

Calibration↗

PubMed2002

Knowledge-based system for method development of chiral separations with capillary electrophoresis using highly-sulphated cyclodextrins.

Method development for chiral separations is not easy because it requires experience and many experimental possibilities can be chosen. In order to help the analyst, a knowledge-based system (KBS) for the rapid determination of experimental parameters, which allow a baseline separation of enantiomers, has been developed. On the basis of own laboratory knowledge, completed with literature data, rules were defined and a KBS was built. Five different techniques are considered in this KBS. This paper describes the capillary electrophoresis (CE) section, in which a strategy has been defined based on the use of highly-sulfated cyclodextrins as chiral selectors. A structured representation of the knowledge and its implementation in Toolbook software is presented.

Artificial Intelligence↗

PubMed2001

Quantitative structure-retention and retention-activity relationships of beta-blocking agents by micellar liquid chromatography.

Sixteen beta-blocking agents (acebutolol, alprenolol, atenolol, bisoprolol, carteolol, celiprolol, esmolol, labetalol, metoprolol, nadolol, oxprenolol, pindolol, practolol, propranolol, sotalol and timolol) showing a large range of hydrophobicity (octanol-water partition coefficients, log P between -0.026 and 2.81) were subjected to micellar liquid chromatography with sodium dodecyl sulfate as micelle forming agent, and n-propanol as organic modifier. The correlation between log P and the retention factor extrapolated to a mobile phase free of micelles and organic modifier was investigated. The use of an interpolated retention factor or the retention factor for specific individual experimental mobile phases was however advantageous since the retention factors of all beta-blocking agents were measurable in the selected mobile phases. Good correlations with log P and with in vitro biological parameters (cellular permeability coefficients in Caco-2 monolayers and apparent permeability coefficients in rat intestinal segments) were found.

Adrenergic beta-Antagonists↗

PubMed2001

Development and validation of a high-performance liquid chromatographic method for the determination of gamma-hydroxybutyric acid in rat plasma.

A method for the determination of gamma-hydroxybutyric acid (GHB) in rat plasma was developed using solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with UV detection. GHB was isolated from plasma using strong anion-exchange SPE columns. The chromatographic separation was performed on a C18 Aqua column. The lower limit of quantification was 10 microg/ml using 60 microl of plasma. The linearity of the calibration curves was satisfactory as indicated by correlation coefficients of >0.990. The within-day and between-day precision were <10% (n=24), the accuracy was nearly 101%. Plasma concentrations in rats after GHB infusion determined by HPLC-UV were compared with the corresponding concentrations determined with a validated gas chromatographic-mass spectrometric method by orthogonal distance regression. A good correlation was observed and a t-test indicated no significant differences from 0 and 1 for the intercept and slope, respectively.

Animals↗

PubMed2001

Evaluation of dissolution profiles using principal component analysis.

The performance of principal component analysis (PCA) for the evaluation of dissolution profiles is examined and compared with other methods such as the similarity factor and the calculation of the area under the curve. Both simulated and real data from the pharmaceutical industry are used. The PCA scores plots of the dissolution curves provide information about the between- and within-batch variations. Differences in level or shape can be observed in the first two principal components (PCs). Irrelevant irregularities, which have a strong influence on the similarity factor, are neglected in PC1/PC2. To detect outliers in a set of dissolution curves, PCA was preferred above Hotelling's T2 test. In general, PCA is found to be a useful technique to examine dissolution data visually, but however, it does not contain criteria to decide if batches are similar or not. This can be done by combining PCA with the resampling with replacement or bootstrap method to construct confidence limits.

Solubility↗

PubMed2001

Rapid screening for chiral separations by short-end injection capillary electrophoresis using highly sulfated cyclodextrins as chiral selectors.

Two series of amino acid derivatives and phenylamines were used to evaluate the potential of highly sulfated cyclodextrins (HS-CDs) for the screening for chiral separations by capillary electrophoresis (CE). HS-CDs showed to be very versatile and to exhibit very high enantioselectivity. The use of short-end injection allowed to reduce dramatically the analysis time. From the results obtained, a scheme for the rapid screening of enantiomeric molecules was developed and applied to various chiral drugs. Results are very satisfying as almost all compounds (62 out of 67) could be baseline-resolved. Usually, less than three experiments were necessary to obtain very good separation.

Acids↗

PubMed2001

Optimization of the chiral separation of some 2-arylpropionic acids on an avidin column by modeling a combined response.

The enantiomeric separation of some nonsteroidal antiinflammatory drugs was investigated on an avidin column. An experimental design approach (central composite design) was used to evaluate the effects of three method parameters (pH, concentration of organic modifier, and buffer concentration) on the analysis time and the resolution, as well as to model these responses. This revealed that the organic modifier concentration and sometimes the pH are significant parameters to control because of their influence on both analysis time and resolution. Furthermore, the central composite design results were combined in a multicriteria decision-making approach in order to obtain a set of optimal experimental conditions leading to the most desirable compromise between resolution and analysis time.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2001

Screening of an enterovirus specific RT-PCR ELISA method for the quantification of enterovirus genomes in human body fluids by means of a three-level experimental design.

In order to obtain a detection limit as low as possible for a quantitative enterovirus specific RT-PCR ELISA assay, optimal reaction conditions, which give rise to the highest response, need to be determined. This was done by investigating the influence of 13 factors, selected from RT and PCR, in a multivariate approach by means of a well-balanced three-level screening design, derived from a three-level Plackett--Burman design. Optimal reaction conditions could be determined by calculation and evaluation of the effects of the different factors on the response, i.e. the measured absorbance of the ELISA detection. The method will be used to study a possible longitudinal relationship between enteroviruses and the development of multiple sclerosis and juvenile diabetes.

Body Fluids↗