The role of inertial particle collectors in evaluating pharmaceutical aerosol delivery systems.

Design theory for cascade impactors is well developed, and design principles can be summarized quite succinctly. The key geometric parameters of three commonly used impactors have been compared to design guidelines. Calibration theory and practice have undergone improvement in recent years. Published results show distinctly different characteristics for three commonly used impactors, and conformance to modern design recommendations results in desirable performance characteristics. A consideration of the sensitivity of stage collection efficiency characteristics to geometric variables and flow rate indicates that measurement of certain physical dimensions is sufficient to assure that impactor performance matches that of a properly calibrated unit. Flow rate is an important operating variable that is more likely to fall out of its calibrated range than important dimensional variables resulting from instrument manufacturing. In practice, data from impactors are frequently treated as though the impactors have ideal collection characteristics. The practical effects of impactor nonideal performance can be demonstrated by model calculations, and these show the necessity of data inversion to obtain a size distribution. The process is not straightforward for unknown distributions. There are much smaller differences between ideal and real performance for an impactor complying with design guidelines, thus, the cutoff characteristics are sharp.

Assessment of the twin impinger for size measurement of metered-dose inhaler sprays.

The calibration of the first stage of the twin-stage impinger, an instrument proposed for use in measuring the spray size from metered-dose inhalers, was performed with monodisperse aerosols by a standard technique for cascade impactors. The mean cut point was found to be not particularly sensitive to operating variables which may be expected to occur in practice. The cut point was close to that reported previously, although the collection efficiency curve was found to be slightly sharper. Calculations are reported on the expected results of measurements on aerosols in a two-stage instrument with an idealized perfect collection efficiency curve as well as the curve measured for the twin impinger. These results indicate that important characteristics of spray size distribution cannot be distinguished with an ideal two-stage instrument; the twin impinger is less capable than an ideal instrument.

A personal cascade impactor: design, evaluation and calibration.

A cascade impactor has been developed that is suitable for personal sampling. The impactor can be used with four, six, or eight stages with cut points ranging from 0.5 micron to 21 micron aerodynamic diameter. Although the impactor can be operated over a fairly wide flow rate range, it is designed specifically to be operated at 2 L/min so that a personal sampler may be used as the air mover. The nozzles of the impactor are radial slots with six slots per stage for the first six stages. Circular nozzles arranged in a radial pattern are used for the last two stages. On each stage, the area between the nozzles is used as the impaction surface for the stage before it. This design allows for the impactor to be compact, rugged and lightweight (170 gm for the four-stage design). The impactor stages are contained in a mounting bracket that can be clipped to the lapel or pocket. Although the impactor is designed for personal use, it also can be used as a compact impactor for general sampling tasks. The particle cut-off characteristics of each stage and the interstage losses were determined using monodisperse aerosols. The particle losses were found to be low and the cut-off characteristics sharp. Thus, size distributions can be obtained as accurately as with larger cascade impactors.

Personal sampling impactor with respirable aerosol penetration characteristics.

Single stage impactors with penetration characteristics approximating those of the BMRC, AEC and ACGIH respirable criteria have been developed for use as personal samplers. Three impactors were built for flow rates of 2 L/min. Experimental calibration data of these impactors are compared to the respective respirable criteria for which they were designed. Oil soaked impaction plates were used in these impactors so particles impacting on the plates would always strike an oiled surface and not bounce from the plate. Experiments with coal dust using these plates showed little particle bounce. Finally, a procedure is introduced by which samplers can be designed with penetration characteristics that differentiate between the AEC and ACGIH respirable criteria.

A portable optical particle counter system for measuring dust aerosols.

A portable battery-operated optical particle counter/multichannel analyzer system has been developed for the numbers size distribution and number concentration measurement of light-absorbing irregular-shaped dust particles. An inertial impactor technique has been used to obtain calibration curves by relating the magnitude of the optical counter's signal to the particle's aerodynamic or Stokes' diameter. These calibrations have been made for aerosols of coal, potash, silica, rock (copper ore), and Arizona road dust particles.

An evaluation of the GCA respirable dust monitor 101-1.

The GCA RDM 101-1 has been evaluated using aerosols of coal, Arizona road dust, silica, potash, and rock (copper ore) particles. The effects of the dust mass concentration, particle size distribution, and dust material on the instrument response were investigated. The instrument was found to measure the mass concentrations of respirable dust aerosols up to about 16 mg/m3 for coal and rock dust and about 20 mg/m3 for silica, potash, and Arizona road dust, providing there is not appreciable mass in the size range below approximateley 0.7 micrometer aerodynamic diameter.

A dust generator for laboratory use.

A dust generator has been developed to produce dry dust from powderous materials for instrument calibration and laboratory studies. The powder is fed at a constant rate via a chain conveyor into a fluidized bed where the particles are deagglomerated and aerosolized. The powder feed rate is raviable from 1.2 to 36 mm3/min and the air flow rate from 9 to 30 Lpm. Aerosols of coal, silica, potash, rock, and Arizona road dust have been successfully generated for calibrating optical particle counters and aerosol mass monitors.

Precision aerosol divider.

A precision aerosol divider with a 17 to 1 flow split has been designed and tested. The divider, primarily a mass monitor calibration device, collects 94.4% of the aerosol on a filter to serve as a standard and delivers 5.6% of the aerosol to the mass monitor to be calibrated.