摘要：An enzymic determination of ammonia-nitrogen with L-glutamate dehydrogenase has been applied, not only to blood but in water analysis, and an attempt was made to develope a simple procedure for routine analysis of water samples by the usual photometric technique. The sample was mixed with a substrate solution consisting of NADH and α-ketoglutarate (α-KG), and incubated with an enzyme solution. At the end of enzymic reaction, absorbance at 340 nm reached a minimum and showed a stable value. Difference in absorbance between blank and final reaction mixture agreed well with the theoretical value, and was proportional to the amount of ammonia-nitrogen. It required a few to 12 minutes to complete the enzymic reaction, and the length of time depended on the amount of enzyme solution added. Ammonia-nitrogen existing as chloramine in a mixture of ammonium chloride and sodium hypochlorite was determined similarly by the enzymic method, and although the value obtained by former method was a little high than by the indophenol method. This error in enzymic determination was derived from larger decrease of OD 340 nm of NADH by the action of available chlorine of chloramine, and was eliminated by the addition of thiosulfate. Additionally, ammonia in chloramine was found to be unstable and tend to undergo decomposition, so that addition of thiosulfate is necessary to a sample containing chloramine. Thiosulfate gave no adverse effect on the enzymic determination of ammonia. Presence of the following amount of substances in a sample did not interfere in the enzymic determination of ammonia-nitrogen : Cr6+, As3+ 0.05 mg/l ; Mn2+, Fe3+, 0.3 mg/l ; Pb2+, nitritenitrogen 0.1 mg/l ; nitrate-nitrogen 10 mg/l ; F-0.8 mg/l ; SO2-4, Ca2+ 200 mg/l ; Mg2+ 100 mg/l ; silicate 30 mg/l.
