The electrical charge carried by inhalation aerosols has been found to affect device performance and lung deposition of Dry Powder Inhalers (DPI), Metered Dose Inhalers (MDI) and nebulizers. The Dekati® ELPI™ (Electrical Low Pressure Impactor, Dekati Ltd.) has been widely used to determine the charge size distribution of inhalation aerosols. However, where the ELPI™ method gives the net charge of the particles the Dekati® Bipolar Charge Analyzer (Dekati® BOLAR™) is the first commercially available instrument capable of measuring bipolar electrical charge size distribution of inhalation aerosols. 

The Dekati® BOLAR™ can separately detect positively and negatively charged particles in five different particle size fractions. After the charge measurement, negatively and positively charged particles can also be analyzed enabling measurement of charge to mass ratio in different particle size fractions. This completely new kind of information is needed in the development of inhalable medicine and delivery devices; the positive and negative charge levels carried by particles can vary significantly between different inhaler devices depending on the materials used in the device, the design of the device, carrier and drug particles used in the device and operating conditions. Until now, the measurement of size classified bipolar electrical charge levels has not been possible, which makes the Dekati® BOLAR™ a completely unique tool for inhaler device development.

BOLAR™ features include

  • Bipolar electrical charge size distribution in 5 particle size fractions
  • Separate detection of positively and negatively charged particles
  • Real-time measurement
  • Analysis of collected particles
  • Sample flow rate 30 – 90 lpm
  • Automated test sequence and self check procedures
  • Stand alone operation
  • Standard USP inlet connection
  • Large 7” display with user interface
  • Data stored on a USB drive or network drive via ethernet connection
  • Easy data analysis options for reviewing and analysing charge and mass data

See video of the BOLAR™ unit here.

Yli-Ojanperä, J., Ukkonen, A., Järvinen, A., Layzell, S., Niemelä, V. & Keskinen, J. 2014. Bipolar Charge Analyzer (BOLAR): A new aerosol instrument for bipolar charge measurements. Journal of Aerosol Science, vol 77, pp. 16-30.

The Dekati® Bipolar Charge Analyzer (BOLAR™) has been specifically designed for measuring bipolar charge of inhalation aerosols including DPIs (Dry Powder Inhalers), MDIs (Metered dose inhalers) and nebulizers. The charge carried by inhalation aerosols has been found to affect both inhaler device performance and lung deposition. Thus far particle charge studies have focused on particle net charge measurements since a method for measuring bipolar charge has not been available. These studies have, however, indicated that net charge measurements give insufficient information as the particles generated by one inhaler device can simultaneously carry both positive and negative charge. The Dekati® BOLAR™ is the solution for this and is the first commercially available instrument that can simultaneously measure both negative and positive charges.

The BOLAR™ features have been designed to meet the needs of inhaler device development:

  • The instrument inlet is designed for a standard USP port connection where the inhaler device can be connected to.
  • The measurement cycle is programmed for short time scale measurement (~ 1 min), each cycle consist of data quality verification procedures.
  • Repeatability of the measured inhaler can be easily viewed after the measurement on the BOLAR™ display. Consecutive measurement cycles can be shown simultaneously on the screen for comparison.
  • Different data saving options are available ensure protection of the data.
  • Instrument calibration and measurement cycle details can be programmed to be only accessed with a password and thus avoid user errors.
  • Data processing tools have been designed to easily analyze repeatability and reproducibility of measurements of individual shots or actuations
  • Particles collected inside the bipolar detectors can be analyzed to determine the charge to mass or drug to carrier ratio in different particle size fractions and for different polarity particles.



Leung, S.S., Chiow, A.C., Ukkonen, A. & Chan H.K. Applicability of Bipolar Charge Analyzer (BOLAR) in Characterizing the Bipolar Electrostatic Charge Profile of Commercial Metered Dose Inhalers (MDIs). Pharmaceutical Research 09/2015. DOI 10. 1007/s11095-015-1786-z

Wong, J., Lin, Y.W., Kwok, P., Niemelä, V., Crapper, J. & Chan, H.K. Measuring Bipolar Charge and Mass Distributions of Powder Aerosols by a Novel Tool (BOLAR). 2015. Molecular Pharmaceutics 2015, 12(9). pp. 3433-3440. DOI:10.1021/acs.molpharmaceut.5b00443.

Wong., J., Kwok, P. C. L., Niemelä, V., Heng, D., Crapper, J., Chan, H.-K., Bipolar electrostatic charge and mass distributions of powder aerosols – Effects of inhaler design and inhaler material, J Aerosol Sci., 95, 104-117, 2016


Particle size range 0.1 - 12.8 µm
Number of size fractions 5
Number of electrometers                                                        17
Sampling rate 10 Hz
Sensitivity 10 pC
Flow rate 60 lpm (30-90 lpm)
Data storage USB or network drive via ethernet                                
Pump requirements* 35-95 lpm @ 400 mbar depending
on the used sample flow rate
Dimensions 670 x 552 x 595 mm
Unit weight 90 kg
Operating Conditions 10 - 35 °C
0 - 90% RH non-condensing
Inlet connection Standard USP inlet





*Suitable pumps available at Dekati Ltd.

Impactor cutpoints

Branch D50%
1 0.94 µm
2 2.84 µm
3 4.47 µm
4 8.07 µm
5 12.79 µm





The Dekati® Bipolar Charge Analyzer measures particle bipolar electrical charge size distribution. The instrument consists of two main components: a flow divider and electrical collection tubes. The flow divider is carefully designed to divide the sample evenly into six branches. Five of these branches lead the sample to bipolar detectors and the sixth one is connected to an electrical filter that is used to verify successful flow dividing. The bipolar detector assemblies consist of a pre-separator impactor and two nested cylinders which measure the bipolar charge carried by the particles. The impactor has a different cut point in each of the five branches enabling detection of different particle size fractions in different bipolar detector tubes.

The bipolar detector itself consists of two concentric cylinders. The inner cylinder is at high positive potential creating an electrical field between these two cylinders. The particle sample travels in a gap between the two cylinders where positively charged particles drift to the outer cylinder and negatively charged particles drift to the inner cylinder. Both cylinders are connected to electrometers that measure separately the amount of negative and positive charge carried by the particles. A back-up filter is placed at the end of each bipolar detector to collect neutral particles that may exist in the sample. The bipolar detector cylinders can be uncoupled after measurement and particles collected in different cylinders analyzed. This way the device can be used to measure bipolar charge distribution in respect of particle mass and particle composition in five different size fractions.


Bipolar detector operation

Dekati® BOLAR™ brochure

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