Inhalation Device Development

Why is charge important?

The charge carried by inhalation aerosols has been found to affect both inhaler device performance and lung deposition. The charge levels have been found to be affected by materials used in the device, drug and carrier material used in the formulation, interaction between surfaces and the device, but can also be affected by environmental conditions such as temperature and humidity. Thus far particle charge studies have focused on particle net charge measurements with e.g. the ELPI®+ which enables detection of particle net charge distribution in 14 size fractions. Since the ELPI®+ operation is based on impactor technology, it can simultaneously be used to measure net charge distribution and gravimetric mass size distribution of the aerosol to gain charge to mass ratio.

Though the ELPI®+ is a useful tool for determining particle net charge distribution, it is not able to distinguish negatively and positively charged particle but is measuring net charge of the aerosol. To gain more detailed information on particles’ charge state, the bipolar charge size distribution of the particles can be measured. The Dekati® BOLAR is the right tool for this and is the first commercially available instrument that can simultaneously measure both negative and positive charges.



The Dekati® ELPI®+ has been widely in pharmaceutical inhaler studies to measure particle concentration, size distribution and charge. ELPI®+'s main advantages in pharmaceutical inhalation aerosol studies are its wide operational size range (6nm -10µm), possibility to analyse the size classified particles after the measurement for drug-carrier ratio in different size fractions, fast time response and a unique ability to measure net charge distribution of the particles. The real-time operation of the ELPI®+ enables fast assessment of burst-to-burst repeatability and reproducibility of the inhaler.

The ELPI®+ can be used to:

  • Detect particle number concentration and size distribution in real-time (e.g. the repeatability of the inhaler device).
  • Make gravimetric impactor measurements to determine particle mass size distribution.
  • Collect the size classified samples in the impactor for further analysis.
  • Determine particle net charge levels in different size fractions.

For more information on charge measurements, see the Dekati® Bipolar Charge Analyzer.



Glover, W. & Chan, H.-K. 2004. Electrostatic charge characterization of pharmaceutical aerosols using electrical low-pressure impaction (ELPI). Journal of Aerosol Science 35, pp. 755-764. 

Telko, M.J., Kujanpää, J. & Hickey, A. 2007. Investigation of triboelectric charging in dry powder inhalers using electrical low pressure impactor (ELPI™). International Journal of Pharmaceutics 226, pp. 352-360.