Detection and Counting of Ultrafine Particles in Ultrapure Water Using Laser Breakdown Acoustic Method

Ultrafine particles, with a size and number density comparable to those of particulate impurities in ultrapure water, were counted individually by the proposed laser induced breakdown acoustic method. The detection conditions and counting efficiency of the particles were investigated theoretically, and the design conditions of the optical system for counting the ultrafine and ultradilute particles was obtained. Using 0.038 µm polystyrene ultrafine particles, which is one of the smallest standard particles on the market, particle counting at the number density of ultrapure water level, 102 particles per 1 ml, was demonstrated, and it was shown that the minimum detectable particle size was at least one order smaller than that of the conventional laser scattering method. The validity and applicability to in-line monitoring using a flow-type cell and size distribution measurements applying the pulse height distribution of the breakdown acoustic signals were also confirmed.