Opw

Stage 1 Stage 2 Stage 3

Stage 4

Stage 1 Stage 2 Stage 3

Stage 4

Inlet airflow

Inlet airflow

Figure 12.16 (a) The multistage liquid impinger. (Reproduced from G. W. Hallworth. Br. J. Clin. Pharm., 4, 689 (1977).) (b) The principal features affecting the performance of inertial impactors: air flow, the dimensions S and T, the diameter of the jet, D*, the density, p, and the diameter of the particles, d. The trajectory of particles which are too small to deposit is shown.

Reproduced from G. W. Hallworth, in Drug Delivery to the Respiratory Tract (ed. D. Ganderton and T. Jones), Ellis Horwood, Chichester, 1987.

Trajectory of particle too small to impact

Figure 12.16 (a) The multistage liquid impinger. (Reproduced from G. W. Hallworth. Br. J. Clin. Pharm., 4, 689 (1977).) (b) The principal features affecting the performance of inertial impactors: air flow, the dimensions S and T, the diameter of the jet, D*, the density, p, and the diameter of the particles, d. The trajectory of particles which are too small to deposit is shown.

Reproduced from G. W. Hallworth, in Drug Delivery to the Respiratory Tract (ed. D. Ganderton and T. Jones), Ellis Horwood, Chichester, 1987.

can be washed to reveal the extent of fall-out of large particles. The smallest particles of all reach the collecting solvent.

Because of the need for standardisation of test equipment, the British Pharmacopoeia and other compendia have adopted detailed specifications for impinger devices. Two impinger devices have been adopted by the British Pharmacopoeia. Apparatus 'A' is shown in Fig. 12.17. All these operate by dividing the dose emitted from an inhaler into the respirable and nonrespirable fractions. The device in Fig. 12.17 employs the principle of liquid impingement and has a solvent in both chambers to collect the aerosol. Air is drawn through the system at 60 dm3 min 1 and the inhaler is fired several times into the device. There are several impaction surfaces at the back of the glass throat about 10 cm away from the activator oc

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