Measuring The Bipolar Charge Distributions of Fine Particle Aerosol Clouds of Commercial PMDI Suspensions Using a Bipolar Next Generation Impactor (bp-NGI)

Purpose To measure the charge to mass (Q/M) ratios of the impactor stage masses (ISM) from commercial Flixotide™ 250 μg Evohaler, containing fluticasone propionate (FP), Serevent™ 25 μg Evohaler, containing salmeterol xinafoate (SX), and a combination Seretide™ 250/25 μg (FP/SX) Evohaler metered dose inhalers (MDIs). Measurements were performed with a purpose built bipolar charge measurement apparatus (bp-NGI) based on an electrostatic precipitator, which was directly connected below Stage 2 of a Next Generation Impactor (NGI). Methods Five successive shots of the respective MDIs were actuated through the bp-NGI. The whole ISM doses were electrostatically precipitated to determine their negative, positive and net Q/m ratios. Results The ISM doses collected in the bp-NGI were shown to be equivalent to those collected in a standard NGI. FP particles, actuated from Flixotide™ and Seretide™ MDIs, exhibited greater quantities of negatively charged particles than positive. However, the Q/m ratios of the positively charged particles were greater in magnitude. SX particles from Serevent™ exhibited a greater quantity of positively charged particles whereas SX aerosol particles from Seretide™ exhibited a greater quantity of negatively charged particles. The Q/m ratio of the negatively charged SX particles in Serevent™ was greater in magnitude than the positively charged particles. Conclusions The bp-NGI was used to quantify the bipolar Q/m ratios of aerosol particles collected from the ISMs of commercial MDI products. The positive charge recorded for each of the three MDIs may have been enhanced by the presence of charged ice crystals formed from the propellant during the aerosolisation process.