Often simply referred to as capacitance, radio-frequency (RF) impedance has been used for over two decades to measure online biomass. It is generally regarded as the most robust and reliable method to monitor live-cell concentrations in mammalian cell culture (1). Many biopharmaceutical companies have now made the transition from conventional glass or stainless steel multiuse (MU) vessels to single-use (SU) bioreactors. Disposables are rapidly becoming the preferred platform for new processes requiring current good manufacturing practice (CGMP) compliance. At the…