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A Van Schepdael

Publications and source records attributed to A Van Schepdael.

At least 19 recordsLinked to original sources
PubMed2006

Characterization of impurities in dirithromycin by liquid chromatography/ion trap mass spectrometry.

With a recently developed liquid chromatographic (LC) method, using a phosphate buffer, several unknown impurities present in dirithromycin samples were separated. In this paper, a reversed-phase liquid chromatography-tandem mass spectrometry method is described for the investigation of dirithromycin and related substances. The method employed uses a Zorbax Extend C18 column (250 mm x 4.6 mm I.D.), 5 microm, and a mobile phase consisting of acetonitrile, 2-propanol, water and ammonium acetate solution pH 8.5. Mass spectral data are acquired on an LCQ ion trap mass spectrometer equipped with an electrospray ion (ESI) source operated in the positive ion mode. The LCQ is ideally suited for the identification of related substances because it provides on-line LC/MS(n) capability, which allows efficient identification without time-consuming isolation and purification procedures. Using this method, the fragmentation behavior of dirithromycin and its related substances was studied and the unknown impurities occurring in commercial samples were investigated. In total the structures of nine impurities were elucidated, among which three were different analogues with a modification in the side chain on the oxazine ring. Two impurities showed a different alkyl group in position C13. In two impurities the desosamine sugar was involved with changes in the degrees of methylation of the amino group. One unknown impurity was identified as dirithromycin F and another unknown was characterized as dirithromycin N-oxide.

Chromatography, Liquid↗
PubMed2006

Investigation of vancomycin and related substances by liquid chromatography/ion trap mass spectrometry.

Liquid chromatography (LC) methods compatible with mass spectrometry (MS) that are suitable for impurity profiling of vancomycin mixtures have not been described in the literature. The mobile phases of the existing methods contain non-volatile additives and/or solvents that give problems in combination with MS. In this paper, a reversed-phase LC/tandem mass spectrometry method is described for the investigation of vancomycin and related substances. The LC method uses a Zorbax Extend C18 column (250 x 4.6 mm i.d.), 5 microm, and a mobile phase consisting of methanol, water and ammonium acetate solution (pH 9.0). This method allows us to separate vancomycin and its impurities. Mass spectral data are acquired on an LCQ ion trap mass spectrometer equipped with an electrospray interface operated in the positive and negative ion modes. The LCQ is ideally suited for identification of impurities and related substances because it provides on-line LC/MSn capability, which allows efficient identification without time-consuming isolation and purification procedures. Using this method, the fragmentation of vancomycin and known derivatives was studied and the structures of six substances occurring in commercial samples were elucidated.

Anti-Bacterial Agents↗
PubMed2003

Interlaboratory study of a liquid chromatography method for erythromycin: determination of uncertainty.

Erythromycin is a mixture of macrolide antibiotics produced by Saccharopolyspora erythreas during fermentation. A new method for the analysis of erythromycin by liquid chromatography has previously been developed. It makes use of an Astec C18 polymeric column. After validation in one laboratory, the method was now validated in an interlaboratory study. Validation studies are commonly used to test the fitness of the analytical method prior to its use for routine quality testing. The data derived in the interlaboratory study can be used to make an uncertainty statement as well. The relationship between validation and uncertainty statement is not clear for many analysts and there is a need to show how the existing data, derived during validation, can be used in practice. Eight laboratories participated in this interlaboratory study. The set-up allowed the determination of the repeatability variance, s(2)r and the between-laboratory variance, s(2)L. Combination of s(2)r and s(2)L results in the reproducibility variance s(2)R. It has been shown how these data can be used in future by a single laboratory that wants to make an uncertainty statement concerning the same analysis.

Anti-Bacterial Agents↗
PubMed2003

Determination of kanamycin in serum by solid-phase extraction, pre-capillary derivatization and capillary electrophoresis.

An effective method based on solid-phase extraction (SPE) and capillary electrophoresis (CE) for the determination of kanamycin in human serum was developed and validated. Off-line SPE was employed for the isolation of kanamycin from serum on a carboxypropyl-bonded phase (CBA) weak cation-exchange cartridge. A mixture of 0.2 M borate (pH 10.5)-methanol (50:50, v/v) was used as analyte eluting solvent. After pre-capillary derivatization with o-phthalaldehyde/mercaptoacetic acid reagent, the sample was analyzed by CE with a separation buffer of 30 mM borax, pH 10.0, containing 16% (v/v) methanol. A linear response over the concentration range 5-40 microgram/ml was obtained with a detection limit of 2 microgram/ml. Intra-day and inter-day precision were 6.2 and 10.3% RSD, respectively. Recoveries of approximately 90% were found. For the determination of lower levels of kanamycin (<5 microgram/ml), NH(4)OH (25%, w/v)-methanol (30:70, v/v) was used for analyte elution. After evaporation, reconstitution and derivatization, the sample was analyzed by on-line field-amplified sample stacking (FASS) CE. Good linearity in the concentration range 0.4-5 microgram/ml was obtained with a detection limit of 0.1 microgram/ml. Intra-day and inter-day RSD were 3.4 and 11.2%, respectively. Recoveries of approximately 60% were found. The method was successfully applied to the analysis of kanamycin in sera of tuberculosis patients at peak level and trough level concentrations.

Anti-Bacterial Agents↗
PubMed2003

Analysis of unknown compounds in azithromycin bulk samples with liquid chromatography coupled to ion trap mass spectrometry.

A selective reversed-phase liquid chromatography/mass spectrometry (LC/MS(n)) method is described for the identification of azithromycin impurities and related substances in commercial azithromycin samples. Mass spectral data are acquired on an LCQ ion trap mass spectrometer equipped with an atmospheric pressure chemical ionization interface operated in positive ion mode. The LCQ provides on-line LC/MS(n) capability, making it ideally suited for identification purposes. In comparison with UV detection, this hyphenated technique provides as its main advantage efficient identification of novel substances without time-consuming isolation and purification procedures. Using this technique, six novel related substances detected in commercial azithromycin samples have been studied.

Anti-Bacterial Agents↗
PubMed2003

Solid-phase synthesis of polymyxin B1 and analogues via a safety-catch approach.

As part of a program towards the development of novel antibiotics, a convenient method for solid-phase synthesis of the cyclic cationic peptide polymyxin B1 and analogues thereof is described. The methodology, based on cleavage-by-cyclization using Kenner's safety-catch linker, yields crude products with purities ranging from 37-67%. Antibacterial assays revealed that analogues 23-26, in which the (S)-6-methyloctanoic acid moiety is replaced with shorter acyl chains, exhibit distinct antimicrobial activity. The results suggest that the length of the acyl chain is rather critical for antimicrobial activity. On the other hand, substitution of the hydrophobic ring-segment D-Phe-6/Leu-7 in polymyxin B1 with dipeptide mimics (i.e. analogues 27-33) resulted in almost complete loss of antimicrobial activity.

Bacillus↗
PubMed2002

Study of the stability of polymyxins B(1), E(1) and E(2) in aqueous solution using liquid chromatography and mass spectrometry.

Polymyxins B(1), E(1) (colistin A) and E(2) (colistin B) were subjected to degradation in aqueous solutions of different pH values (1.4, 3.4, 5.4 and 7.4) and at different temperatures (37, 50 and 60 degrees C) in order to investigate the characteristics of decomposition. The progress of decomposition was followed by reversed-phase liquid chromatography on YMC-Pack Pro, C-18 stationary phase. The degradation curves showed (pseudo) first order kinetics. The pH-rate profiles indicate that colistin is more susceptible to degradation in solutions of pH above 5 and is more stable in acidic media. The degradation of polymyxin B(1) was most rapid at pH 7.4. Qualitative analysis of the degradation products by LC/MS reveals that racemization is the major mechanism of degradation in both acidic and neutral media.

Anti-Bacterial Agents↗
PubMed2001

Analysis of clindamycin by micellar electrokinetic chromatography with a mixed micellar system.

This study details the development and validation of an optimized method with micellar electrokinetic chromatography for the analysis of clindamycin. The method uses a mixed micellar phase containing anionic sodium dodecylsulfate (SDS) and non ionic Brij 35 on an untreated fused-silica capillary. The influences of buffer concentration, pH, SDS, Brij 35 and organic modifier were investigated. Special attention was given to the role of the non ionic Brij 35 in the mixed micellar system. Optimization with a central composite design resulted in optimal separation conditions: background electrolyte containing 25 mM sodium tetraborate pH 7.75, 90 mM SDS, 14 mM Brij 35 and 21% acetonitrile. The applied voltage was 15 kV and the capillary temperature 15 degrees C. The method was robust and gave good linearity and repeatability. The limits of detection and quantitation were 0.05 and 0.15%, respectively, relative to a 2.5 mg/ml clindamycin solution. Two commercial bulk products were analysed with this system.

Anti-Bacterial Agents↗
PubMed2001

Development and validation of a simple capillary zone electrophoresis method for the analysis of kanamycin sulfate with UV detection after pre-capillary derivatization.

Capillary zone electrophoresis was successfully applied to separate eight related substances of kanamycin and several minor unknowns from the main component. Strategies to enhance derivatization and selectivity and to optimize separation parameters involved the application of experimental designs. This chemometrical approach considers main effects as well as interactions of the influential parameters, thus conducting a more thorough investigation of the method than the common step-by-step approach. Central composite face centered designs established optimal separation conditions: 30 mM borax buffer, pH 10.0 containing 16.0% (v/v) methanol and optimal composition of derivatization reagent: 27 mg/ml 1,2-phthalic dicarboxaldehyde and 25 microl/ml mercaptoacetic acid in borate buffer, pH 10.4. The standard curves were linear over the concentration range of 0.007-1.01 mg/ml for the main component and 0.003-0.1 mg/ml for the related substances. The limit of quantitation was 0.14% (m/m) for the related substances and impurities (S/N= 10). The assay method was used to determine the composition of several commercial samples. Quantitative analysis indicates potential usefulness of capillary electrophoresis as an alternative to the assay method prescribed in the European Pharmacopoeia and the United States Pharmacopeia.

Anti-Bacterial Agents↗
PubMed2001

Isolation and structural characterization of polymyxin B components.

Polymyxin B is a peptide antibiotic complex present as sulphate. The components were separated preparatively on a poly(styrene-divinylbenzene) (PLRP-S), 1000 A, 8 microm, 250 x 12.5 mm I.D. stationary phase maintained at 60 degrees C and using 215 nm detection. Elution was carried out with acetonitrile-sodium sulphate solution (0.7%, m/v; pH adjusted to 2.5 with trifluoroacetic acid)-water (18:50:32, v/v) at a flow-rate of 4.0 ml/min. Seven polymyxin B components were isolated and characterized using 1H and 13C NMR. The molecular masses were confirmed by mass spectrometry. The structures of two components were determined for the first time. Polymyxins B5 and B6 were identified as having the same composition as polymyxin B1 except that the fatty acid moiety was nonanoic acid and 3-hydroxy-6-methyloctanoic acid, respectively.

Chromatography, Liquid↗
PubMed2001

Structure elucidation of four related substances in gramicidin with liquid chromatography/mass spectrometry.

A selective reversed phase liquid chromatography/mass spectrometry (LC/MS(n)) method is described for the identification of related substances in commercial gramicidin samples. Mass spectral data are acquired on an LCQ ion trap mass spectrometer equipped with an electrospray interface operated in the positive and the negative ion mode. The LCQ is ideally suited for identification of related substances because it provides on-line LC/MS(n) capability. Compared with UV detection the main advantage of this hyphenated LC/MS(n) technique is the efficient identification of novel related substances without time-consuming isolation and purification procedures. Using this method four novel related substances were separated and identified in a commercial sample.

Amino Acid Sequence↗
PubMed2001

Analysis of metacycline by capillary electrophoresis.

The development and validation of an optimized capillary electrophoresis method for the determination of metacycline in the presence of its related substances by capillary electrophoresis is shown. The influence of methanol as organic modifier, buffer pH, buffer concentration, capillary length, column temperature, Triton X-100 and methyl-beta-cyclodextrin was investigated. A central composite design was performed in order to optimize the method. The optimal separation conditions were: uncoated fused-silica capillary (39 cm total length, 31 cm effective length, 50 microm ID); as background electrolyte a solution of 160 mM sodium carbonate and 1 mM EDTA (pH 10.35)/methanol (89:13 v/v); temperature, 15 degrees C; voltage, 12 kV. The method showed good selectivity, repeatability, linearity, and sensitivity. The limits of detection and quantitation are 0.024% and 0.06%, respectively, relative to a 2.5 mg/mL solution. Six commercial samples were analyzed quantitatively.

Automation↗
PubMed2001

Analysis of bacitracin by micellar electrokinetic capillary chromatography with mixed micelle in acidic solution.

A method used for quantitative analysis of bacitracin with micellar electrokinetic capillary chromatography (MEKC) is described. As capillary zone electrophoresis gave poor separation selectivity, MEKC was preferable. It was found that a zwitterionic surfactant, 3-(N,N-dimethylhexadecylammonium)-propanesulfonate (PAPS) gave the best selectivity among the several surfactants studied. As the analytes tend to adsorb onto the capillary wall due to their positive charge, an acidic solution composed of Tris-phosphate buffer at pH 2.5 was necessary to diminish such adsorption. The peak tailing caused by relatively strong ion pair interaction between the analyte and PAPS micelle could be reduced by adding nonionic surfactant Brij 35 to the PAPS solution. This phenomenon is possibly explained by a mixed micelle mechanism. In order to obtain the optimal conditions and to test the method robustness, a central composite experimental design was performed. The optimal conditions are as follows: 44 cm length of fused-silica capillary with 50 microm inner diameter, 90 mM Tris-phosphate buffer (pH 2.5) containing 17 mM PAPS and 0.3% w/v-Brij 35, 18 kV applied voltage, UV detection at 192 nm and 25 degrees C column temperature. Under the optimal conditions, more than 50 peaks could be obtained in 30 min. The method had a linearity range from 1 to 0.05 mg/mL (concentration of bacitracin A). The limit of quantitation (LOQ) and limit of detection (LOD) were 0.005 and 0.0012 mg/mL, respectively.

Bacitracin↗
PubMed2001

Michaelis-Menten analysis of bovine plasma amine oxidase by capillary electrophoresis using electrophoretically mediated microanalysis in a partially filled capillary.

A method for determining bovine plasma amine oxidase (PAO; EC 1.4.3.6) activity with benzylamine (Bz) as substrate is described. Electrophoretically mediated microanalysis (EMMA) combined with micellar electrokinetic capillary chromatography (MEKC) was used to perform an on-capillary enzymatic reaction and to separate the generated benzaldehyde from the other reaction products. The capillary was only partially filled with the separation solution, since the enzyme was unstable in the presence of the applied surfactant. The initial reaction velocity of the enzyme-catalyzed reaction was estimated from the peak area of the enzyme product, benzaldehyde. An amplification step was introduced by means of an on-capillary incubation of 15 min, in order to accumulate enough reaction product to detect spectrophotometrically at 254 nm. This set-up resulted in a fully automated assay, which can be carried out in less then 35 min. Using the Lineweaver-Burk equation, an average Michaelis constant (K(M)) for PAO was calculated to be 0.74 mM +/- 0.05 mM, which is consistent with previously reported values.

Amine Oxidase (Copper-Containing)↗
PubMed2001

Analysis of vancomycin and related impurities by micellar electrokinetic capillary chromatography. Method development and validation.

A fast and highly selective micellar electrokinetic capillary chromatography (MEKC) method for quantitative analysis of vancomycin and related impurities is described. Among the tested surfactants, cetyltrimethylammonium chloride (CTAC) offered the best selectivity. Another important parameter, which strongly influenced the selectivity, was buffer pH. It was found that the selectivity increased with buffer pH decreasing from 9 to 5. Using Tris-phosphate buffer containing CTAC, satisfactory separation could be obtained in the pH range from 5.0 to 5.5. Excellent repeatability in terms of migration time and peak area could be obtained when the capillary was carefully washed between two runs. In order to obtain optimal conditions and to evaluate the method robustness, a central composite experimental design was carried out. The optimal conditions were: 44 cm length of fused-silica capillary with 50 microm ID, 120 mM Tris-phosphate buffer (pH 5.2) containing 50 mM CTAC, -15 kV applied voltage, UV detection at 210 nm, and a column temperature of 25 degrees C. Under the optimal conditions, more than 20 peaks could be separated within 8 min. The method has a linearity range from 0.004 to 1.2 mg/ml (concentration of vancomycin B, active component). The limit of detection (LOD) and limit of quantitation (LOQ) were 0.4 microg/mL vancomycin, equivalent to 0.3 microg/mL vancomycin B (0.04%) and 1.1 microg/mL vancomycin, equivalent to 0.9 microg/mL vancomycin B (0.1%), respectively.

Aminoglycosides↗
PubMed2001

Electrophoretically mediated microanalysis of gentamicin with in-capillary derivatization and UV detection.

This paper describes a system for integration of a one-step-microscale chemical derivatization and analysis by a methodology known as electrophoretically mediated microanalysis (EMMA). Differential electrophoretic mobility between an analyte, reagent, and their product offers EMMA a unique capability to selectively carry out electrophoretic mixing, control product formation, and separation. This system was successfully applied to perform derivatization and separation of the multicomponent aminoglycoside antibiotic gentamicin using 1,2-phthalic dicarboxaldehyde and mercaptoacetic acid as labeling reagents. A multivariate approach based on central composite experimental design was used to optimize the derivative yield. Full automation of the derivatization and analytical procedure, high derivatization efficiency, high sample throughput, and precision are the excellent features of the present method. In addition, this methodology offers short analysis time, as well as selectivity and sensitivity suitable for impurities determination. Separation of gentamicin C1, C1a, C2, C2a, C2b, sisomicin, and several minor components was achieved. For the first time separation and identification of three impurities, namely garamine, 2-deoxystreptamine, and paromamine are described.

Anti-Bacterial Agents↗
PubMed2001

Isolation and structural characterization of colistin components.

Preparative-scale separation of colistin sulphate bulk sample was carried out on a preparative poly(styrene-divinylbenzene) stationary phase. Isocratic elution with acetonitrile-sodium sulphate solution (0.7% m/v; pH adjusted to 2.5 with TFA) - water (16:50:34, % v/v/v) was carried out at a flow rate of 4.0 ml min(-1). Six colistin components were isolated and characterized using 1H and 13C NMR. The molecular weights were confirmed by mass spectrometry. The structures of 2 components were determined for the first time. Polymyxin E7 was identified as having the same composition as polymyxin E1, except that the fatty acid moiety was 7-methyloctanoic acid. Isoleucine polymyxin E8 was characterized as having the same composition as isoleucine polymyxin E1 with 7-methylnonanoic acid as the fatty acid moiety.

Anti-Bacterial Agents↗