This paper is concerned with pH process control based on sensitivity analysis, applied to a strong acid-strong base system. The models were developed, using the concept of chemical reaction invariants. Derived from GMC synthesis, a non-linear PI control law was presented and the results compared to the classical PI controller. The presence of uncertainties or a shift in the system's behavior has been considered, either on steady state or from the dynamic point of view. ne analysis showed that sensitivity presents the same behavior in both cases, thus demonstrating the feasibility of the application with the nonlinear PI controller. The results of sensitivity analysis indicate a strategy for improving control structure performance, using the concept of fictitious smoothing tanks, inserted into computer codes for process control, yet without incurring appreciable computational load or additional costs.