To facilitate optimal process control limiting substrates must be identified, moni-tored and controlled. Amino acids are often critical substances, especially in mam-malian 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 understand-ing in a shorter time and facilitate process control.