There is a constantly growing demand for monoclonal antibodies for therapeutic and diagnostic applications. Due to this trend the development of new and cost-efficient purification methods is of high importance. This study investigates the separation of a monoclonal antibody from model impurity bovine serum albumin using anionic polyelectrolytes. Different types and molecular weights of anionic polyelectrolytes were screened for their applicability as precipitation agents. Polyanetholesulfonic acid was identified as most promising candidate. Furthermore, the influence and interactions of various parameters on antibody precipitation were investigated by means of Design of Experiments. Design of Experiments provided a fast identification of influencing parameters and parameter interactions. The strongest influence on yield and selectivity of precipitation showed the polyelectrolyte concentration and its interaction with the pH value and the sodium chloride and bovine serum albumin concentration. The interactions identified showed, that parameters should be investigated and optimized together, not stand-alone. (c) 2014 Elsevier B.V. All rights reserved.