Home About us Contact
|
Home About us Contact | ||
|
|
||
Methanol Content (methanol + content)
Selected AbstractsChromatographic evaluation and comparison of three ,-cyclodextrin-based stationary phases by capillary liquid chromatography and pressure-assisted capillary electrochromatographyELECTROPHORESIS, Issue 19 2008Bo Lin Abstract Enantiomer separations were performed on three ,-cyclodextrin-based chiral stationary phases (CSP) containing the pernaphthylcarbamoylated ,-cyclodextrin (CSP 1), peracetylated ,-cyclodextrin (CSP 2) and permethylated ,-cyclodextrin (CSP 3) as chiral selectors by capillary liquid chromatography and pressure-assisted capillary electrochromatography in this study. Triethylammonium acetate/MeOH or phosphate buffer/MeOH was used as the mobile phase. The experimental factors affecting chiral separations have been examined for each CSP, including pH of the buffers, methanol content and applied voltage. Under optimal separation conditions, a number of racemic compounds were resolved into their enantiomers on three cyclodextrin-based CSP. A comparative study on the performance of three CSP revealed the presence of carbonyl functional groups as well as aromatic rings in the cyclodextrin derivatives, enhanced the interaction between the analytes and CSP, and thus improved enantioselectivity of the CSP. [source] An evaluation of the robustness of the Tanaka characterization protocol for reversed-phase liquid chromatography columnsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 16 2005Patrik Petersson Abstract The robustness of the popular ,Tanaka' LC column characterization protocol has been evaluated by the statistical tools of reduced factorial design, multiple linear regression and principal component analysis. These have shown that in order to obtain reliable and reproducible results, it is especially important to control the methanol content, the temperature and, in the case of the total ion-exchange capacity test (,B/P pH 7.6), the pH of the mobile phase. In particular, the hydrophobicity tests (kPB and ,) are sensitive to small changes in methanol content. Provided that the operating parameters for the Tanaka column characterization protocol are controlled within the following experimental limits, i. e. methanol content ±0.5% v/v, temperature ±3°C, pH ±0.10 and buffer concentration ±2.0 mM, it is feasible to distinguish between RP materials that possess selectivity differences larger than their batch-to-batch reproducibility. These experimental requirements can be easily met by current LC instrumentation. Hence, the validity of the Tanaka testing protocol for characterizing columns has been verified. [source] Enatiomeric analysis of simendan by CE with , -CD as chiral selector compared with CMPA-HPLCBIOMEDICAL CHROMATOGRAPHY, Issue 10 2004Famei Li Abstract The chiral separation of simendan enantiomers using capillary electrophoresis was studied with , -cyclodextrin (, -CD) as chiral selector. The in,uences of the concentration and pH of borate buffer solution, , -CD concentration and methanol content in the background electrolyte were investigated. These factors were compared with those in an HPLC with , -CD as chiral mobile phase additive (CMPA-HPLC). The quanti,cation properties of the developed CE method were examined. A baseline separation of simendan enantiomers was achieved in the background electrolyte of 20 mmol/L borate buffer (pH 11.0) containing 12 mmol/L , -CD-methanol (50:50 in volume ratio). The CE method is comparable with CMPA-HPLC in chiral resolution, although the optimal pH in CE (11.0) is much higher than that (6.0) in CMPA-HPLC. This chiral CE method is applicable to the quantitative ananlysis and enantiomeric excess value determination of l -simendan. Copyright © 2004 John Wiley & Sons, Ltd. [source] Model-based characterization of an amino acid racemase from Pseudomonas putida DSM 3263 for application in medium-constrained continuous processesBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2007M. Bechtold Abstract The amino acid racemase with broad substrate specificity from Pseudomonas putida DSM 3263 was overproduced and characterized with respect to application in an integrated multi-step process (e.g., dynamic kinetic resolution) that,theoretically,would allow for 100% chemical yield and 100% enantiomeric excess. Overexpression of the racemase gene in Escherichia coli delivered cell free extract with easily sufficient activity (20,50 U,mg,1 total protein) for application in an enzyme membrane reactor (EMR) setting. Model-based experimental analysis of a set of enzyme assays clearly indicated that racemization of the model substrates D - or L -methionine could be accurately described by reversible Michaelis,Menten kinetics. The corresponding kinetic parameters were determined from progress curves for the entire suitable set of aqueous-organic mixtures (up to 60% methanol and 40% acetonitrile) that are eligible for an integrated process scheme. The resulting kinetic expression could be successfully applied to describe enzyme membrane reactor performance under a large variety of settings. Model-based calculations suggested that a methanol content of 10% and an acetonitrile content of 20% provide maximum productivity in EMR operations. However product concentrations were decreased in comparison to purely aqueous operation due to decreasing solubility of methionine with increasing organic solvent content. Finally, biocatalyst stability was investigated in different solvent compositions following a model-based approach. Buffer without organic content provided excellent stability at moderate temperatures (20,35°C) while addition of 20% acetonitrile or methanol drastically reduced the half-life of the racemase. Biotechnol. Bioeng. 2007; 98: 812,824. © 2007 Wiley Periodicals, Inc. [source] A validated enantiospecific method for determination and purity assay of clopridogrelCHIRALITY, Issue 10 2009Katarina Nikolic Abstract A new and accurate HPLC method using ,-cyclodextrin chemically bonded to spherical silica particles as chiral stationary phase (CSP) was developed and validated for determination of S -clopidogrel and its impurities R -enantiomer and S -acid as a hydrolytic product. The effects of acetonitrile and methanol content in the mobile phase and temperature on the resolution and retention of enantiomers were investigated. A satisfactory resolution of S -clopidogrel active form and its impurities was achieved on ChiraDex® column (5 ,m, 4 × 250 mm) at a flow rate of 1.0 ml/min and 17°C using acetonitrile, methanol and 0.01 M potassium dihydrogen phosphate solution (15:5:80 v/v/v) as mobile phase. The detection wavelength was set at 220 nm. The method was validated in terms of accuracy, precision, linearity, and robustness. The limit of detection for R- enantiomer and S -acid were 0.75 and 0.09 ,g/ml, respectively, injection volume being 20 ,l. Finally, the molecular modeling of the inclusion complexes between the analytes and ,-cyclodextrin was performed to investigate the mechanism of the enantiorecognition and to study the quantitative structure,retention relationships. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source] | |||||||||||||