No abstract

Dopa and carbidopa, components of the dual therapy for Parkinson's disease treatment, are both provided as single enantiomers, since their D-forms are inactive. To ensure the efficiency and safety of the therapy, these D-enantiomers, therefore, should be considered as impurities. In this paper, the enantioseparation power of different types of cyclodextrins, both neutral and charged ones, on dopa and carbidopa enantiomers was tested. Three methods of simultaneous separation of dopa and carbidopa enantiomers were developed, using highly sulfated beta-cyclodextrin and sulfated beta-cyclodextrin as chiral selector, in normal and reversed polarity mode. Two methods among these three were found sensitive enough for the quantitation of 0.1% D-enantiomers in L-forms (impurity level). After the optimization study, the best method was selected, using 16 mM sulfated beta-cyclodextrin in 15 mM sodium phosphate buffer pH 2.45, an uncoated fused-silica capillary (50 num inner diameter, 30 cm total length), and an applied voltage of -12 kV. This method is robust and efficient, with very high resolution for all peaks within a short analysis time of 10 min. Quantitatively, the method offers a limit of detection (LOD) of 0.2 nug/mL and a limit of quantitation (LOQ) of 0.5 nug/mL for both D-dopa and D-carbidopa, which is equivalent to 0.02% and 0.05% against the respective L-enantiomers. A linear relationship was found between the concentration of the analyte and the corresponding peak area in a range of 0.5-2.0 nug/mL.

No abstract

Analyses of statistical variance were applied to evaluate the precision and practicality of a CD-based NACE assay for R-timolol after enantiomeric separation of R- and S-timolol. Data were collected in an interlaboratory study by 11 participating laboratories located in Europe and North America. General qualitative method performance was examined using suitability descriptors (i.e. resolution, selectivity, migration times and S/N), while precision was determined by quantification of variances in the determination of R-timolol at four different impurity levels in S-timolol maleate samples. The interlaboratory trials were designed in accordance with the ISO guideline 5725-2. This allowed estimating for each sample, the different variances, i.e. between-laboratory (s2(Laboratories)), between-day (s2(Days)) and between-replicate (s2(Replicates)). The variances of repeatability (s2r) and reproducibility (s2R) were then calculated. The estimated uncertainty, derived from the precision estimates, seems to be concentration-dependent above a given threshold. This example of R-timolol illustrates how a laboratory can evaluate uncertainty in general.

No abstract