Westech Scientific Instruments (Westech)

Westech Scientific Instruments (Westech)

- 8 Stage Impactor for Testing of DPIs



The aerodynamic particle size distribution of the drug leaving an inhaler device can define the manner in which an aerosol deposits in the respiratory tract during inhalation. This characteristic of the aerosol is often used in judging inhaler performance and is particularly relevant in the development of inhalation formulations during research, production, quality assurance and equivalency testing. The results of characterisations using cascade impaction techniques are additionally used for the determination of fine particle fraction or fine particle dose which may be correlated to the dose or fraction of the drug that penetrates to the lung during inhalation by a patient.


Dry Powder Inhaler (DPI) testing could require added options for preventing stage overloading and necessary to acheive the specified pressure drop through the device. Upper stage mass overloading can be prevented with the addition of a high capacity preseparator or pre-collector. The feature traps non-inhalable aerosols. To acheive the proper pressure drop of 4 kPa (40.8 cm water) in the inhaler, a higher vacuum flow rate at 60 or 90 L/minute may be needed. Higher flow rate application kits include additional stages for maintaining traditional cut point ranges with minimal setup effort. All DPI application options work together to acheive quality analytical results.

Westech 8-stage impactors are specifically designed to meet the highest criteria laid down in the various Pharmacopoeia (e.g. United States Pharmacopeia Chapter; European Pharmacopoeia Chapter 29.9.18 for characterising aerosol clouds emitted by inhalers). By analysing the drug deposited on the individual stages and the final filter, the Fine Particle Fraction, the Fine Particle Dose, the Mass Median Aerodynamic Diameter (MMAD) and Geometric Standard Deviation (GSD) can all be calculated.

Apparatus D of the EP and Apparatus 1 of the USP clearly define the specifications of the Westech 8-stage impactor for use in the testing of inhalers. The standard device with the inclusion of the Induction Port, a compatible mouth-piece adaptor and a suitable pump calibrated to the required flowrate (28.3 lpm) with the impactor in place and shown to be leak tight can be used without modification to characterise the inhaler output.

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