To facilitate optimal process control limiting substrates must be identified, monitored and controlled. Amino acids are often critical substances, especially in mammalian processes. Measurement and thus monitoring is tedious and rarely done. In this application note, we demonstrate how two different analyzers for amino acids, namely HPLC-FLD and Cedex® Bio HT, can be connected on-line to the reactor us-ing the automated sampling system Numera. On the example of a CHO process, it is shown how the on-line availability of the data may increase process understanding in a shorter time and facilitate process control.