Electrostatic charge characterization of pharmaceutical aerosols using electrical low-pressure impaction (ELPI)

A novel method for characterizing the electrostatic charge in pharmaceutical aerosols was developed. Electrical low-pressure impaction (ELPI) was modified and optimized to allow the measurement of aerosol particles from metered dose inhalers (MDIs) for anti-asthmatic drugs. Two commonly used MDIs, VentolinTM and FlixotideTM, were investigated for the charging properties of their emitted aerosols. VentolinTM aerosol was found negatively charged, whilst FlixotideTM aerosol was bipolarly charged, containing both positive and negative charged particles. The electrostatic charge measurements for both MDIs were reproducible with %CV ranging from 3.3% to 12.5% for 10 actuations from each of the inhalers. In addition, chemical assay was undertaken to obtain mass distributions of the aerosol collected inside the ELPI. Both MDIs showed that only a small amount of the drug was recovered from the submicron size range where a large amount of charge was present (negative charge for VentolinTM and positive for FlixotideTM). For the FlixotideTM, the majority of drug was recovered from the 1 to 10 μm particles which were negatively charged. Hence, different particle size fractions of the aerosol can contribute differently to the charge which can feasibly be studied by the ELPI method.