An HPLC method was developed and subsequently validated for the quantitation of cromolyn sodium and its related substances in cromolyn sodium drug substance and Cromolyn Sodium Inhalation Solution, 1.0%. The current USP monograph for cromolyn sodium assay is a non-selective UV method while related substances are determined by TLC. The TLC method, as written in the USP, does not meet the sensitivity requirements as dictated by current regulations. The HPLC method described in this paper provides more accurate and selective quantitation of cromolyn sodium and its two known potential impurities, cromolyn diethyl ester (Impurity 1) and hydroxy phenoxy 2-propanol (Impurity 2). The method development involved the evaluation of several factors including mobile phase composition, column choice and configuration, wavelength evaluation, sind response factors. Chromatographic parameters include a mobile phase of methanol I buffer (45/55; v/v) and a Nova-Pak C-8, 3.9 x 150 mm column, maintained under ambient conditions. The wavelength of choice to maximize the detection of the related substances was 326 nm. Relative response factor for Impurity 2 was determined to be 0.58. Impurity 1 is not stable in an aqueous environment and eventually hydrolyzes to cromolyn sodium. The structural difference between cromolyn sodium and Impurity I is insignificant; therefore, a relative response factor of 1.0 was assigned to Impurity I. The described method is linear, reproducible, accurate; and selective over a range of 0.05% - 2.0% of the working analytical concentration (1 mg/mL) for related substances and 46% - 137% of the analytical working concentration (0.2 mg/mL) for assay. The method precision, relative standard deviation (RSD), among 6 independent samples was not more than 0.4% for the assay and not more than 4.0% for the related substances; Repeatability at the 0.05% (0.0005 mg/mL, n=3) was 2.3%. The intermediate precision was 0.8% (n=18) for assay and 7.8% (n=18) for related substances. The mean absolute recovery for the cromolyn assay between 46 - 137% was 99.9%. The mean absolute recovery for the cromolyn related substance range of 0.05 - 2.0% was 98.5%. Selectivity was evaluated by subjecting the Drug Substance Sample Preparation for assay (0.2 mg/mL) to thermal, basic, oxidative, and UV stress conditions. Cromolyn precipitates under acidic conditions where the pH < 2.0. No significant interference in the analysis of degradation products and impurities was observed. Cromolyn sodium was very sensitive to base and light stress. Consequently, the validated method for the determination of cromolyn sodium and its related substances in cromolyn sodium drug substance and Cromolyn Sodium Inhalation Solution, 1.0% is regarded as stability-indicating.
