On-line high-performance liquid chromatography method for analyte quantitation from pressurized metered dose inhalers

A sensitive and rapid, on-line reversed-phase high-performance liquid chromatographic method for quantitation of compounds at low concentrations in pressurized metered dose inhaler (MDI) systems was developed. Traditional methods for the quantitation of compounds in MDI formulations involve the opening of the MDI vial along with sample dilution prior to quantitation. The new method, reported in this study, involves a direct injection from the MDI vial into the needle injector port of a manual injector. Since there is no dilution step involved, this method can be used to quantitate low concentrations of compounds in MDIs with excellent precision. In addition, since the method requires a small injection volume of 5 microl, repeated analyses can be performed in order to generate multiple data points using the same MDI vial. Validation of the method was performed using ethanol-1,1,1,2-tetrafluoroethane (134a)-based MDIs. Beclomethasone dipropionate (BDP), a corticosteroid used for the treatment of asthma, was used as a model compound. Phase separation studies were conducted to investigate the miscibility of the ethanol-134a mixtures with different mobile phase solvent compositions. For the MDI systems in this study, an acetonitrile-water (90:10, v/v) mobile phase at a flow rate of 0.9 ml/min was found to give acceptable chromatography for BDP on a Apollo C18 5 microm, 150 mm x 4.6 mm column (Alltech Associates, Deerfield, IL, USA). Ultraviolet detection was done at 240 nm and the retention time of BDP was 2.7 min. The on-line HPLC method was characterized to be accurate, precise, sensitive, and specific.