Determinationof nitrite, nitrate and ammonium nitrogens in soil by fia

Abstract

A FIA system was developed for the rapid and continuous determination of nitrite, nitrate and ammonium nitrogens in soil by spectrophotometry. Nitrite nitrogen was determined by using of N-(l-naphthyl)ethylene-diamine. The reagent and sample solutions were injected in the order of reagent (40 µl), sample (40 µl) and reagent (40 μl) by a 16-port injection valve in carrier solution (deionized water). Ten meters long Teflon tubing (0.5 mm i.d.) was used as a reaction coil and maintained at 90°C. Nitrate ion was reduced to nitrite ion with a Cu-Cd column and determined by the same method as that for nitrite nitrogen. For determination of ammonium nitrogen, molecular ammonia was liberated by 1 M NaOH which was injected in both sides of sample solution. Molecular ammonia was separated by means of a tubular microporous poly(tetrafluoroethylene) membrane into a mixed reagent stream in the inner tube and determined by indophenol method. The method developed has been successfully applied to the analyses of soil extracts. The linear relationship between the signal and concentration were obtained for nitrite, nitrate and ammonium nitrogens in the range of 0.1~7, 1~20 and 1 ~ 150 ppm, respectively. The relative standard deviation was 0.3~0.5%. The analysis time required for one sample was about 10 min. © 1989, The Japan Society for Analytical Chemistry. All rights reserved.