Patent ID: 7805983

Claim:
A method for measuring the number of fine particles in ultrapure water using a filtration device for measuring the number of fine particles in ultrapure water, the filtration device comprising: a hollow fiber membrane unit constituted by sealing one end of a hollow fiber membrane having a skin layer capable of trapping the fine particles in the ultrapure water at least on an inner surface thereof by setting a pore diameter of the skin layer equal to or less than a particle diameter of each of the fine particles and fixing a fixing member to an outer periphery between the sealed portion and an open portion via a resin mold part; a water drain part external cylinder connected to one side of the fixing member while internally equipped with the sealed portion of the hollow fiber membrane; and a water supply part external cylinder connected to the other side of the fixing member while internally equipped with the open portion of the hollow fiber membrane and having a water supply port and a blow water drain port through which the ultrapure water supplied from the water supply port is discharged, the method, comprising: passing the ultrapure water from the water supply port of the water supply part external cylinder toward the blow water drain port; subjecting the ultrapure water to internal pressure filtration through the hollow fiber membrane while discharging part of the ultrapure water supplied from the water supply port of the water supply part external cylinder to the blow water drain port; exposing the inner surface of the hollow fiber membrane; and measuring the number of fine particles on the exposed inner surface.