A plurality of particles of from about 5 nm to 100 .mu.m possessing predetermined isoelectric points in the pH range from about 2.5 to 11 is used in a method of detection of a plurality of analytes, wherein the isoelectric particles of each isoelectric point further contain a label and a member of a binding pair capable of interacting with a selected analyte. The particles that formed specific binding pairs are recovered and separated by isoelectric focusing, followed by the detection of the labels associated with the particles. A flow cytometer may be used as a detector of the isoelectric particles.