Uncertainty assessment from robustness testing applied on an LC assay for R-timolol and other related substances in S-timolol maleate

Ruggedness and robustness testing

Due to the strict regulatory requirements, especially in pharmaceutical analysis, analysis results with an acceptable quality should be reported. Thus, a proper validation of the measurement method is required. In this context, ruggedness and robustness testing becomes increasingly more important. In this review, the definitions of ruggedness and robustness are given, followed by a short explanation of the different approaches applied to examine the ruggedness or the robustness of an analytical method. Then, case studies, describing ruggedness or robustness tests of high-performance liquid chromatographic (HPLC), capillary electrophoretic (CE), gas chromatographic (GC), supercritical fluid chromatographic (SFC), and ultra-performance liquid chromatographic (UPLC) assay methods, are critically reviewed and discussed. Mainly publications of the last 10 years are considered.

Robustness testing of a chiral NACE method for R-timolol determination in S-timolol maleate and uncertainty assessment from quantitative data

A robustness test of a capillary electrophoresis method for the chiral separation of timolol in nonaqueous acidified media was performed. A two-level Plackett-Burman design was applied in which one qualitative and six quantitative factors were examined. Resolution, migration times and relative migration times to pyridoxine (selected as internal standard) were examined as qualitative responses to evaluate electrophoretic performance. A quantitative response, the content of R-timolol in S-timolol maleate sample, was also considered. Even though some significant factor effects were observed on the qualitative responses, it was still possible to quantify the R-timolol in the S-timolol maleate samples properly. The quantitative response was not significantly affected by the selected factors, demonstrating the robustness of the procedure. However, the use of different HDMS-beta-CD batches seemed to affect both types of responses necessitating to introduce a warning in the procedure. Since the experiments of the Plackett-Burman design can be assimilated to laboratories in an interlaboratory study, uncertainty can be evaluated using the robustness test data. The robustness test was set-up in such a way that the required variances could be estimated.

Robustness study of a reversed-phase liquid chromatographic method for the analysis of carboxylic acids in industrial reaction mixtures

The robustness study of the reversed-phase liquid chromatographic method developed for the quantitative analysis of carboxylic acids is a real asset to prepare method transfer because it provides an indication of its reliability during routine use. Indeed, it was possible to predict the consequences of small variations in operating conditions on the responses. The design of experiments approach was applied to model the effects and interactions of a high number of factors varying simultaneously with a limited number of runs. First we identified the factors which potentially affect the chromatographic responses used for carboxylic acids quantitation: detection wavelength (lambda), column temperature (T), acetonitrile ratio in mobile phase (Me), duration of the plateau before the gradient (L) and gradient slope (S). Then we estimated the order of magnitude of realistic variations to assign factor levels. Finally a central composite design was carried out around the nominal conditions defined during method optimization. The statistical treatment of responses (retention factors, and concentrations) showed that the column temperature, the acetonitrile ratio in the mobile phase, the duration of the plateau before the gradient and the gradient slope were the most influent factors. The building of the robust domain from response-surfaces allowed us to give tolerance limits for the factors (216 nm< lambda <222 nm, 49.3 degrees C < T < 51.4 degrees C, 4.90% < Me < 5.18%, v/v, 4.5 min < L < 5.4 min, 9%< S <11%) for which the performances of the method were maintained.

Interlaboratory study of a NACE method for the determination ofR-timolol content inS-timolol maleate: Assessment of uncertainty

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.

Nonaqueous capillary electrophoresis method for the enantiomeric purity determination of S-timolol using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin: validation using the accuracy profile strategy and estimation of uncertainty

Nonaqueous capillary electrophoresis (NACE) was successfully applied to the enantiomeric purity determination of S-timolol maleate using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) as chiral selector. With a background electrolyte made up of a methanolic solution of 0.75 M formic acid, 30 mM potassium camphorsulfonate and containing 30 mM HDMS-beta-CD, the determination of 0.1% of R-timolol in S-timolol could be performed with an enantiomeric resolution of 8.5. Pyridoxine was selected as internal standard. The NACE method was then fully validated by applying a novel strategy using accuracy profiles. It is based on beta-expectation tolerance intervals for the total measurement error which includes trueness and intermediate precision. The uncertainty of measurements derived from beta-expectation tolerance intervals was estimated at each concentration level of the validation standards. To confirm the suitability of the developed and validated method, several real samples of S-timolol maleate containing R-timolol maleate at different concentrations were analysed and the results were compared to those obtained by liquid chromatography.