Ammonia abatement in an enzymatic flow system for the determination of creatinine in blood sera and urine

The abatement of ammonia in standard solutions, and in human blood and urine samples is achieved by adding suitable amounts of NADPH and α-ketoglutarate to the sample and passing it through a 2-m nylon tube with glutamate dehydrogenase immobilized on the inner wall. The procedure provides removal of 98% of the ammonia (1–5 × 10^?4 M) in the original sample in 50 s. The abatement of ammonia permits the use of an ammonia probe coupled with an immobilized degradative enzyme for the determination of creatinine. Creatinine was determined in clinical blood and urine samples by first removing the ammonia from the sample and then cleaving the creatinine to N-methylhydantoin and ammonia with immobilized creatininase. Only 200 μl of sample is needed and the entire process is conducted in a single flow stream.