Method repeatability (intra-day precision) was evaluated by assaying six injections of sample preparation of the same batch. The mean % assay was 104.78% and was within the acceptance criteria. The% RSD was found to be 0.41%. The results are shown in table 4. The difference in the assay of Erythromycin estolate in Erythromycin 250mg capsules between the preparations is less than 2.0% of %RSD
Robustness of the method was established by determining the assay and system suitability studies of the sample under deliberately modified chromatographic conditions specified under the method like flow rate, column temperature, pH of buffer or buffer strength in % v/v, mobile phase composition and wavelength of lower and higher side of the actual values. The drug concentration was analyzed under these changed experimental conditions. There was no significant change in the retention time and assay of the drug when the flow rate and composition of the mobile phase were changed. The results are illustrated in Table 5.
In view of the fact that the Erythromycin peak was not found in the existing HPLC method, will pose less of a problem using the proposed UPLC method because it is extracted in the solvent. The proposed UPLC method for the assay of Erythromycin estolate in Erythromycin 250mg capsules was accurate, precise, robust, specific, and stability-indicating thus demonstrating a quality by design approach to method development. Due to its shorter runtime, use of an economical and readily available mobile phase, optimized UV detection the method has been proven to be a significant important compared with the reported methods and is compliant with current regulatory requirements. Owing to shorter run time this method enables rapid quantification of many samples in routine and quality-control analysis of various formulations containing Erythromycin estolate.