An apparatus and a method for isolating a biologic product, such as plasmid DNA, from cells. The method involves lysing cells in a controlled manner separate insoluble components from a fluid lysate containing cellular components of interest, followed by membrane chromatographic techniques to purify the cellular components of interest. The process utilizes a unique lysis apparatus, ion exchange and, optionally, hydrophobic interaction chromatography membranes in cartridge form, and ultrafiltration. The process can be applied to any biologic product extracted from a cellular source. The process uses a lysis apparatus, including a high shear, low residence-time mixer for advantageously mixing a cell suspension with a lysis solution, a hold time that denatures impurities, and an air-sparging bubble mixer that gently yet thoroughly mixes lysed cells with a neutralization/precipitation buffer and floats compacted precipitated cellular material.