Patent ID: 6913901

Claim:
A method to control a count of particles per unit volume to be counted in a sample, the method comprising the steps of: preparing a first mixture of a plurality of populations of reference particles in known proportions and known quantities, the reference particles in each of the populations having at least one respective characteristic differing between the populations; adding a known quantity of the first mixture to a known volume of the sample to produce a second mixture containing the particles to be counted and the populations of reference particles; flowing the second mixture past a measuring device: measuring with the measuring device a count of the particles to be counted and a count of the reference particles of each of the populations of reference particles in the second mixture in the flow past the measuring device; calculating an absolute number of the particles to be counted per unit volume in the second mixture from the counts of the particles to be counted in the sample and the reference particles; determining final proportions of the populations of the reference particles in the second mixture; and checking whether the final proportions between the populations of the reference particles in the second mixture correspond to the known proportions between the populations of the reference particles in the first mixture to determine the accuracy of the calculated number of the particles to be counted per unit volume in the second mixture.