1997 Volume 46 Issue 4 Pages 271-274
An 80 ml of sample solution (0.11 mgN) was adjusted to pH 1011 with a sodium hydroxide solution and to 0.01 M EDTA with an EDTA solution, and then diluted to 100 ml with pure water. The treated solution was pumped at 2 ml/min into a converter (18 cm high and 8 mm diameter) containing copper-zinc grains, which converted the nitrate ion to ammonia. As the concentration (activity) of the zinc ion in converter decreased, the reduction efficiency (NO3-→NH3) increased. Thus, EDTA was added to the sample solution to decrease the concentration of zinc ions in the column. The ammonia in the effluent (10 ml) was determined by indophenol colorimetry (final volume, 50 ml). The EDTA in the effluent hardly affected the colorimetric determination of ammonia. When the concentration of EDTA was 0.03 M in the effluent, the absorbance of indophenol blue decreased by 1.6% of the maximum absorbance. Calibration curves of both the nitrate ion and ammonia almost agreed in the region 110 mgNil. The relative standard deviation (n =10) was 0.91 % for 2 mgN/l of the nitrate ion. The nitrate ion in seawater was well determined by this method using the standard-addition method.
