Design and evaluation of a high-flowrate nanoparticle respiratory deposistion (NRD) sampler

A high-flow (10 L/min) nanoparticle respiratory deposition (NRD) sampler was designed and evaluated to facilitate lower limits of quantification (LOQ) for metal nanoparticles than a low-flow (2.5 L/min) version. The high-flow NRD consists of an inlet, impactor stage, diffusion stage, and a final filter. For the impactor stage, three nozzle sections each containing 12 nozzles were designed from theory to achieve a cut-off diameter (d50) of 300 nm. Various depths of 37-mm-diameter 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, 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 drop were measured for all components. The impactor stage with one of the nozzle plates had a d50 of 305 nm. The collection efficiency for the foam with a depth of 7 cm adjusted for presence of the impactor was the closest match to the NPM curve with a R2 value of 0.96. Chemical analysis of the metal content for foam media affirmed that the high-flow NRD would require less sampling time to meet LOQs than the 2.5 L/min NRD. The final filter with a modified support pad had a collection efficiency near 100%. The overall pressure drop of the sampler 4.4 kPa (17.5 in. H2O) limits its ability to operate with available belt-mounted personal sampling pumps, although modifications to the sampler design could eliminate this constraint.