Two important cell culture process parameters that are often monitored in an effort to improve mammalian cell culture are osmolality and pH. Proper control of pH and osmolality can help optimize cell viability and growth by maintaining the isotonicity of the culture medium and regulating the transport of water and nutrients through cell membranes. Samples are typically withdrawn from the bioreactor and passed through a biomedical analyzer such as the NOVA BioProfile 400. While in situ pH measurement is common, it has some inherent technical challenges that reduce the quality of the test results with time. Near infrared spectroscopy can perform in situ real-time monitoring of pH and osmolality and provide closed-loop feedback to the bioreactor controllers. With this input the controllers can adjust culture media conditions to optimize cell performance and productivity. This poster discusses how near infrared spectroscopy can measure ionic concentrations in a bioreactor cell culture process.