Sequential injection analysis as a tool for in situ monitoring of Fe(II), Fe(III), NO3− and NO2− in natural and waste waters Original Research Article

This paper presents a sequential injection analysis (SIA) system for sequential monitoring of Fe(II) and Fe(III), or NO3− and NO2− with typical concentrations of natural and waste waters. Determination of nitrite was based on the Griess–Ilosvay reaction, while the Fe(II) determination was based on the reaction with 1,10-phenantroline. Determination of Fe(III) and NO3− were performed after their reduction, respectively, in Jones and copperized cadmium columns, using forward and reversal flow directions. Tangential filtration permitted the application of the methodology for determination of dissolved species in aquatic suspensions containing particulate matter and sediments. The stability of the analytical curves was verified over periods of 4–5 days. Quantification limits for NO2− and NO3− were 0.01 and 0.02 mg l−1 N, respectively. For Fe(II) and Fe(III) the quantification limits were 0.05 and 0.1 mg l−1, respectively, with a sampling frequency of 20 h−1. The influence of sulphides and natural organic matter on the performance of the reducing columns were evaluated, as well as the use of regeneration solutions.