Determination of Impurities in Ipratropium Bromide and Albuterol Sulfate Inhalation Solution by High Performance Liquid Chromatography

The ipratropium bromide and albuterol sulfate inhalation solution was injected directly. Agilent^© Zorbax SB-Aq C₁₈ column was used as the stationary phase, and the mixed solutions of 6.4 mmol·L^-1 sodium heptanesulfonate solution (adjusting its acidity to pH 3.8 with phosphoric acid) and acetonitrile at different volume ratios were used for gradient elution to separate known and unknown impurities. Detection was performed at the detection wavelength of 210 nm, and all impurities were first assigned (4 common known impurities of ipratropium bromide were identified based on their relative retention time of 0.67, 0.75, 0.83, and 1.32 relative to ipratropium bromide, while 6 common known impurities of salbutamol were identified based on their relative retention time of 2.55, 3.19, 3.40, 3.46, 3.71, and 3.96 relative to salbutamol). The 8 known impurities not studied in the US pharmacopoeia were quantified using the standard curve method, and unknown impurities were quantified using area normalization method (compared to main constituents such as ipratropium bromide or salbutamol). Impurities that could not assigned were analyzed qualitatively and quantitatively with reference to unknown impurities. It was shown that the impurities related to the 2 main constituents were basically consistent under conditions of acid, alkali, illumination, oxidation, high-temperature degradation, and non degradation, indicating that the applicability of the method was good. The resolution of each known compound in the ipratropium bromide and albuterol sulfate inhalation solution was greater than 1.5. Linear relationships between values of the mass concentration of the 8 known inpunities and the peak area were kept in definite ranges, with detection limits (3S/N) in the range of 0.002-0.028 mg·L^-1. Test for recovery was made according to the standard addition method, giving recoveries of the 8 known impurities in the range of 98.4% -102%, and RSDs (n=6) of the determined values were not greater than 1.0%. The proposed method was successfully used for the analysis of actual samples.