The Bipolar Next Generation Impactor (bp-NGI) as a Tool for the Simultaneous Measurement of the Bipolar Charge Distribution and Mass Quantification of Aerosols for Inhalation



Interest in the nature of electrostatic charge build up on aerosol particles for inhalation has grown as pharmaceutical scientists seek to fully understand this complex phenomena and its influence on both pMDI and DPI performance. The net charge to mass ratios of aerosol particles have been measured with systems such as the ELPI [1] and the eNGI [2]. Bipolar charge measuring systems (BCMS) such as those developed by O’Leary et al. [3] and Kulon et al. [4] are capable of measuring the bipolar charge distribution of aerosols particles but are not ideally suitable for simultaneous mass determination. To overcome these limitations, the authors present a novel system for the simultaneous bipolar charge and mass quantification of inhalation aerosol particles using a specially designed Bipolar Next Generation Impactor (bp-NGI). The system utilises an electrostatic precipitation system consisting of both negative and positive electrodes and precipitation tubes which can be connected to any stage of an NGI, to a preseparator or USP throat. Negative and positive high voltages are applied to each electrode allowing electrostatic precipitation of the correspondingly charged aerosol particles onto the inner surfaces of the tubes. The tubes are connected to an electrometer, providing charge measurements of the aerosol particles deposited. The system can subsequently be dismantled and washed down with solvent so that quantification of the aerosol particles via reverse phase HPLC may be performed. The system was successfully employed to quantify the bipolar charge to mass ratios of Flixotide™ 250 pMDI.