Investigation of Electrostatic Properties of Pharmaceutical Powders Using Phase Doppler Anemometry

Electrostatic properties of formulation component materials and blends play an important role in dry powder inhalation (DPI) products. Valid measurement of charge distribution will therefore lead to better control of powder behavior in DPI manufacturing processes. Ultrafine powders are known to have bipolar charge, have nonspherical shapes, and tend to be highly cohesive. Real-time noninvasive techniques need to be developed to obtain a precise and accurate measurement of electrically charged powders, as they aerosolize from a DPI product. How this measure relates to materials behavior throughout the various steps of a manufacturing process, e.g., from drug micronization and blending with lactose to filling dose units, also needs to be addressed. A novel noninvasive technique, which employs the phase Doppler anemometry (PDA) system for simultaneous measurement of size and charge of pharmaceutical powders, is currently being considered. Previous research demonstrated the advantages of this technique in measuring the bipolar charge distribution on a population of liquid aerosols. These findings led to significant improvements in understanding the performance of inhaler formulations, manufacturing processes, and development of new devices for inhaled drug delivery. This paper presents an investigation of electrostatic properties of lactose materials (typically used as a DPI excipient) using the PDA system. PDA calibration was checked using dry polystyrene microspheres, followed by an investigation of different grades of lactose. The PDA technique was used to track the motion of charged particles in the presence of an electric field. The magnitude, as well as the polarity of the particle charge, can be obtained by solving the equation of particle motion combined with the simultaneous measurement of its size and velocity. Results show the capability of the technique to allow real-time charge distribution and size measurement in the control of dry powder attributes that are critical to a better understanding of the manufacturing design space.