Abstract: The concentrations of hyperfine particles in a fluid are monitored by flowing a predetermined quantity of the particle-containing fluid over a substrate in the presence of a force field which "collects" the particles onto the substrate. The particles may be deposited on the substrate according to size, so that one can readily ascertain not only the particle concentration in the fluid, but the size distribution of the particles as well. This technique greatly concentrates the particles so that one can usually detect and monitor materials having extremely small particulate concentrations in the fluid from which they are collected.