1. 1. Solutions containing L-asparagine or L-arginine were pumped through open tube enzyme reactors, the reactors catalyze the convertion of l-asparagine or l-arginine to ammonia, the ammonia concentration in the effluent was determined and found to be directly proportional to the concentration of l-asparagine or l-arginine in the range 3–25 mM and 1–12 mM, respectively. 2. 2. The reactor for l-asparagine determination was prepared by immobilizing asparaginase on the interior surface of a nylon tubing. 3. 3. The reactor for l-arginine determination was prepared by simultaneous immobilization of arginase and urease, this dual enzyme reactor catalyzes two consecutive reactions leading to the formation of ammonia from l-arginine.