Determination of albuterol sulfate and its related substances in albuterol sulfate inhalation solution, 0.5% by RP-HPLC

Abstract

An isocratic reversed-phase high performance liquid chromatographic (RP-HPLC) method has been developed and validated for the determination of albuterol sulfate and six of its related substances in albuterol sulfate inhalation solution, 0.5% (w/v). The separation was achieved using a YMC phenyl column (250 mm × 4.6 mm ID, 5 μm fitted with a direct connect YMC phenyl guard column (20 mm × 4 mm ID) maintained at ambient conditions, and a mobile phase of 25 mM monobasic potassium phosphate (pH 3.0) and methanol (95:5, v/v). The mobile phase flow rate was 1.5 mL/min and the detection wavelength was 225 nm. Albuterol is quantitated versus an external standard. The method was capable of resolving six of the seven known albuterol-related substances. Bis-ether albuterol, a drug substance process related impurity, is retained on the column due to its different hydrophilic character. The related substances are determined by area percent. However, a correction factor of 1.6 is applied for the determination of albuterol aldehyde, a potential impurity and a degradation product, since its molar absorptivity is about 1.6 times that of albuterol. The limits of detection and quantitation for albuterol and six of its related substances ranged between 0.01 and 0.21% of the assay concentration of 0.3 mg/mL as albuterol base. The method was found to be linear for albuterol over the range of 50–150% of the active label claim. The method was also found to be linear for the six related substances over the range 0.05–0.5%. No interferences from the blank, placebo (formulation matrix), related substances or force-degraded placebo samples were observed for the determination of the active or the individual related substances. The method was found to be accurate, precise, linear, specific, sensitive, rugged, robust, and stability-indicating.