A preparative method of isolating a preselected whey protein or group of whey proteins from a solution is provided. The method comprises the following steps: (a) contacting a whey protein solution with the preselected ion exchanger for a time and at a temperature sufficient to enable the preselected whey protein to be adsorbed; wherein the whey protein solution has (1) a protein content in the range of about 5% to about 20% by weight, (2) a pH of a preselected level, which is the level at which the preselected whey protein or group of whey proteins selectively binds to the preselected ion exchanger, and (3) a reduced ionic strength; and (b) recovering either or both of the following: (1) the whey protein component adsorbed in step (a), and (2) the breakthrough whey protein component not adsorbed in step (a). It is preferred that the whey protein solution is a retentate obtained via ultrafiltration of whey, having reduced ionic strength, or a whey protein concentrate powder which has been reconstituted with water.