RESUMEN
Ammonia is the main nitrogenous waste product of cellular metabolism and if accumulated in culture media may limit cell growth and affect the quality of cultured cell lines. Therefore, it is crucial to control levels of this metabolite during the in vitro expansion of human cells. This paper describes the successful application of ion selective electrodes (ISE) to continuously monitor ammonium concentrations in a perfused cell bioreactor. The polymeric membranes of the ISE were cast from carboxylated poly(vinyl chloride) (PVC-COOH) and doped with highly hydrophilic poly(ethylene glycol) (PEG). The PEG was incorporated into the surface of the sensors in order to reduce the effect of biofouling without impairing their analytical characteristics. The electrodes developed enabled fast and selective measurements of ammonia in the range 0.5-5mM, corresponding well with the concentration determined off-line. Additionally, the UV sterilised sensors were small and flexible enough to be readily inserted into the limited space of the bioreactor. Long-term analytical performance of PEG-modified ISE during continuous measurements in mammalian cell cultures was investigated. The sensors remained stable for the duration of the bioprocess, 7 days.