Chiral separations in polar organic solvent chromatography: updating a screening strategy with new chlorine-containing polysaccharide-based selectors.
ABSTRACT The screening conditions of an existing column and mobile phase selection strategy for chiral drug substances in polar organic solvent liquid chromatography (POSC) were tested for their applicability on two new chlorine-containing polysaccharide-based stationary phases. The selectors of these phases are cellulose tris(3-chloro-4-methylphenylcarbamate) and amylose tris(5-chloro-2-methylphenylcarbamate). The enantioselectivity of these phases is compared to that of the four phases (Chiralpak AD-RH, Chiralcel OD-RH, Chiralpak AS-RH and Chiralcel OJ-RH) used in the earlier defined strategy. A test set of 62 structurally diverse chiral drug substances is analyzed using the screening conditions of the strategy on the six phases. The results confirm that the acetonitrile-based mobile phase provides a higher success rate and better resolutions than the methanol-based also on the new phases. However, the importance of the methanol-based mobile phase cannot be neglected for complementarity reasons; the two mobile phases insure enantioselectivity for different compounds. A third (ethanol-based) mobile phase, not part of the strategy, was also used to screen the two new phases. The joint results led to different possibilities to upgrade the current screening strategy so that improved success rates are obtained. The chlorine-containing chiral stationary phases demonstrated to have an added value to the screening process since they provided enantioresolution for compounds not resolved by non-chlorine-containing ones.
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ABSTRACT: Biodegradation of chiral pharmaceuticals in the environment can be enantioselective. Thus quantification of enantiomeric fractions during the biodegradation process is crucial for assessing the fate of chiral pollutants. This work presents the biodegradation of alprenolol and propranolol using an activated sludge inoculum, monitored by a validated enantioselective HPLC method with fluorescence detection. The enantioseparation was optimized using a vancomycin-based chiral stationary phase under polar ionic mode. The method was validated using a minimal salts medium inoculated with activated sludge as matrix. The method was selective and linear in the range of 10-800ng/ml, with a R(2)>0.99. The accuracy ranged from 85.0 percent to 103 percent, the recovery ranged from 79.9 percent to 103 percent, and the precision measured by the relative standard deviation (RSD) was <7.18 percent for intra-batch and <5.39 percent for inter-batch assays. The limits of quantification and detection for all enantiomers were 10ng/ml and 2.5ng/ml, respectively. The method was successfully applied to follow the biodegradation of the target pharmaceuticals using an activated sludge inoculum during a fifteen days assay. The results indicated slightly higher biodegradation rates for the S-enantiomeric forms of both beta-blockers. The presence of another carbon source maintained the enantioselective degradation pattern while enhancing biodegradation extent up to fourteen percent.Ecotoxicology and Environmental Safety 11/2012; · 2.20 Impact Factor
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ABSTRACT: In the search for appropriate chromatographic conditions to separate enantiomers, screening strategies are often applied because achieving chiral separations is tedious. These screenings aim to find relatively fast suitable separation conditions. However, the definition of these screenings mostly relies on years of expertise or on the labour- and time-intensive investigation of a broad range of chiral stationary- and mobile phases. A large amount of data is generated using either approach. In this study, the obtained data are investigated in a systematic manner and (dis)similar systems are searched for. For this case study, 48 chromatographic systems were characterized by the enantioresolutions of 29 racemates. Exploratory data analysis was performed by means of projection pursuit, revealing the different enantioselective patterns of the chromatographic systems. To quantify the (dis)similarity, correlation coefficients and Euclidean distances were calculated. These results were visualized in color maps to allow investigating the degree of (dis)similarity between the systems. These maps proved to be a helpful tool in the selection of dissimilar/orthogonal chromatographic conditions. Hierarchical-cluster-analysis dendrograms were constructed next to evaluate the clustering of similar systems, i.e. with an equivalent enantioselectivity. Screening sequences were extracted and compared with the initial, defined by direct data interpretation. In a final section, selection of dissimilar systems was done by means of the Kennard and Stone algorithm. The systems selected by the applied techniques did not necessarily perform better than the selection by direct data interpretation. Nevertheless, high cumulative success rates are achieved for the selected combinations, due to the broad enantioselectivity, the high individual success rates and the complementarity of the chiral selectors.Journal of Chromatography A 01/2013; · 4.61 Impact Factor
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ABSTRACT: In this study, the screening steps of chiral separation strategies with polysaccharide-based chiral stationary phases were applied on boron cluster compounds in normal-phase liquid chromatography (NPLC) and polar organic solvents chromatography (POSC). Since the screening steps were initially developed to analyze organic compounds, their applicability for boron clusters was investigated. Overall, the screening steps in NPLC were applicable for the separation of zwitterions, while for anions mostly no elution was observed. A hypothesis for the latter behavior is precipitation of anions in the nonpolar mobile phases. Ten out of 11 compounds could be partially or baseline separated on the NPLC screening systems. In POSC, all zwitterions were separated on at least one of the screening systems, with an overall lower retention as in NPLC. Anions were detected but not separated in the majority of the experiments. Also their retention on the chiral stationary phases was very limited. This study showed that the chiral discrimination potential of chemically modified polysaccharides is meaningful for chiral separations of structurally chiral boron cluster species, but needs further systematic research, in which recognition mechanisms should be further explored. In addition, some unusual peaks also indicated that conditions with a high separation efficiency must first be searched for some of the tested systems. Copyright © 2014 John Wiley & Sons, Ltd.Biomedical Chromatography 01/2014; · 1.95 Impact Factor