Design and Evaluation of a High-Flowrate Nanoparticle Respiratory Deposition (NRD) Sampler

A high-flow (10 L/min) nanoparticle respiratory deposition (NRD) sampler was designed and evaluated to achieve reduced limits of quantification (LOQs) for metal nanoparticles. The high-flow NRD consists of an inlet, impactor stage, diffusion stage, and a final filter. An impactor stage with 12 nozzles was designed from theory to achieve a cut-off diameter of 300 nm at 50% particle collection efficiency (d₅₀). Various depths of 37-mm-diameter polyurethane foam cylinders were tested for the diffusion stage to obtain a collection efficiency curve similar to the deposition of nanoparticles in the human respiratory tract, known as the nanoparticulate matter (NPM) criterion. The objective for the final filter was a collection efficiency of near 100% with minimal pressure drop. The collection efficiencies by size and pressure drops were measured for all NRD sampler components. The final design of the impactor stage nozzle achieved a d₅₀ of 305 nm. The collection efficiency for the diffusion stage with a depth of 7 cm when adjusted for presence of the impactor was the closest to the NPM curve with a R² value of 0.96 and d₅₀ of 43 nm. Chemical analysis of the metal content for foam affirmed that the high-flow NRD sampler required less sampling time to meet metal LOQs than the 2.5 L/min NRD sampler. The final filter with a modified support pad had a collection efficiency near 100%. The overall pressure drop of the sampler of 8.5 kPa (34 in. H₂O) could not be handled by commercial personal sampling pumps. Hence the high-flow NRD sampler can be used as an area sampler or without the final filter for collection of nanoparticles.