Autoadaptative sequential injection system for nitrite determination in wastewaters

A novel autoadaptative sequential injection system for the analysis of nitrite is described. The automatic determination uses a direct spectrophotometric method, based on the Griess–Ilosvay reaction. In this method the absorbance of the purple azo dye formed is measured at 555 nm. In the sequential injection operation, the sample and the reagent are aspirated and mixed by reverse flow. The sequencing and overlapping of stacked (reagent) zones as well as selection of volumes have been studied in detail. The proposed analytical system is intelligent, simple and robust, allowing for nitrite determination in a double concentration range, by a simple and automatic programmable operation change. These two ranges are 0.0–3.0 and 0.0–20.0 ppm with detection limits being 0.048 and 0.4 ppm, respectively. Next surroundings have been developed allowing autocalibration and independent monitoring of nitrite concentration. The experimental set-up has been evaluated applying it to real samples analysis of very diverse concentration samples coming from a WWTP. The throughput of the method was 12 samples per hour.