Abstract
A drop (ca. 0.05 ml) of test solution involving ammonia-nitrogen was taken in a small test tube. To it were added with thorough mixing a drop of hypochlorite-carbonate buffer (Dissolve 5 g of NaHCO3 and 8 g of Na2CO3 in 500 ml of water. Then add 100 ml of NaClO with available chlorine 0.3% and dilute to 1 l) and a drop of thymol solution (Dissolve 5 g of thymol in acetone to make 50 ml and add equal volume of 0.7M NaOH solution). It was immersed in a hot water bath (90°C or higher) for 30 sec. to develop blue color of iodothymol. The detection limit was 0.005 μg as N.
Alternatively, The test tube was removed from the water bath, and 2 drops of isobutanol was added with vigorous shaking. After standing, the blue color was transferred into the butanol layer. The detection limit was 0.0025 μg as N.
The reagent blank should be referred to.
