Mensuration and cleaning of the jets in Andersen cascade impactors

Fifty-three Andersen Cascade Impactors (404 stages) have been investigated using an automated visual stage mensuration technique. A cleaning method was suggested for stages with jets smaller than nominal diameters. The impact of nonapproved jet diameters on result parameters from particle size analysis was evaluated theoretically.

The jet diameters were measured using the Andersen Visual Inspection Device. A stepwise cleaning procedure was performed to recover the jets of noncompliant stages, and after each step a new stage mensuration was performed.

The result of this extensive investigation, including measurements of each jet, is compared to other studies, to tolerance limits applied at AstraZeneca Lund and also to limits used by the manufacturer. Sixteen of the investigated stages were outside applied tolerance limits due to too small average diameters. Insertion of a go gauge into every jet of the stages was the only technique of those tested that increased the jet diameters toward nominal dimensions. Moreover, the relative standard deviation of the jet diameters decreased considerably after use of go gauges.

Stage mensuration is a valuable technique for detection of improper jet dimensions of the Andersen Cascade Impactor, and use of go gauges is an effective cleaning method especially for jets with small diameters. However, use of stop/go gauges as a periodical quality control test on a small number of randomly selected jets was a poorly discriminating test, as both compliant and noncompliant stages would most probably pass such a test.