Development and validation of a stability-indicating HPLC method for the determination of cromolyn sodium and its related substances in cromolyn sodium drug substance and cromolyn sodium inhalation solution, 1.0%

An HPLC method was developed and subsequently validated for the quantitatio n of cromolyn sodium and its related substances in cromolyn sodium drug sub stance and Cromolyn Sodium Inhalation Solution, 1.0%. The current USP monog raph for cromolyn sodium assay is a non-selective UV method while related s ubstances are determined by TLC. The TLC method, as written in the USP, doe s not meet the sensitivity requirements as dictated by current regulations. The HPLC method described in this paper provides more accurate and selecti ve quantitation of cromolyn sodium and its two known potential impurities, cromolyn diethyl ester (Impurity 1) and hydroxy phenoxy 2-propanol (Impurit y 2). The method development involved the evaluation of several factors inc luding mobile phase composition, column choice and configuration, wavelengt h 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 relat ed substances was 326 nm. Relative response factor for Impurity 2 was deter mined to be 0.58. Impurity 1 is not stable in an aqueous environment and ev entually hydrolyzes to cromolyn sodium. The structural difference between c romolyn sodium and Impurity I is insignificant; therefore, a relative respo nse 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) f or related substances and 46% - 137% of the analytical working concentratio n (0.2 mg/mL) for assay. The method precision, relative standard deviation (RSD), among 6 independen t samples was not more than 0.4% for the assay and not more than 4.0% for t he 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) f or related substances. The mean absolute recovery for the cromolyn assay be tween 46 - 137% was 99.9%. The mean absolute recovery for the cromolyn rela ted substance range of 0.05 - 2.0% was 98.5%. Selectivity was evaluated by subjecting the Drug Substance Sample Preparati on for assay (0.2 mg/mL) to thermal, basic, oxidative, and UV stress condit ions. Cromolyn precipitates under acidic conditions where the pH < 2.0. No significant interference in the analysis of degradation products and impuri ties was observed. Cromolyn sodium was very sensitive to base and light str ess. Consequently, the validated method for the determination of cromolyn s odium and its related substances in cromolyn sodium drug substance and Crom olyn Sodium Inhalation Solution, 1.0% is regarded as stability-indicating.