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If stage mensuration results in an Effective Diameter in excess of an upper limit, then the stage must be replaced. This is a sign that the nozzles have worn, either as a result of corrosion from the solvents used to dissolve the active drug or erosion from the constant rapid passage of particles through the nozzles concerned. In this case, there is no further option available as it is not practical to reapply metal to impactor nozzles.
The majority of failed stages however relate to cases where the Effective Diameter decreases below the lower limit for the stage. This is usually caused by a build-up of hardened particulates or, more likely, because the corrosion process products metal salts that occlude the nozzle.
In this instance, a combination of ultrasonic cleaning and “stage pinning” is often sufficient to remove deposits and restore performance.
Impactor Stage Pinning involves pushing stainless steel “go” pins with a diameter between the nominal diameter and the lower tolerance limit for the stage through each nozzle in order to clear accumulated debris.
For comprehensive product details, specifications and part numbers, please request a copy of our brochure “Quality Solutions for Inhaler Testing”.
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