SIMULTANEOUS DETERMINATION OF AMMONIA NITROGEN AND L-GLUTAMINE IN BIOREACTOR MEDIA USING FLOW-INJECTION

A novel split stream flow injection (FI) system suitable for the simul taneous determination Of L-glutamine and ammonia nitrogen (ammonia-N) in cell culture media is described. Potentiometric detection of ammoni a-N in one portion of the manifold is achieved using a commercial ammo nia gas-sensing electrode fitted with a wall-jet cap. L-Glutamine is q uantified in the other part of the split sample by potentiometric dete ction of ammonium ions (by an ammonium-selective polymer membrane elec trode), liberated from the hydrolysis of glutamine after the sample fl ows through a glass bead reactor containing immobilized glutaminase. E ndogenous ammonia-N and potassium ions that would normally interfere w ith the glutamine measurement are removed upstream using a unique tubu lar cation-exchange unit. Using 50 mul sample volumes and mixed soluti ons of ammonium chloride and L-glutamine in Iscove's Modified Dulbecco 's Medium to calibrate the Fl measuring system, values for ammonia-N a nd L-glutamine determined for 22 media samples obtained from a bioreac tor growing retroviral producer cells correlate well with those measur ed with commercial, manual enzymic-spectrophotometric assay kits.