Automatic System for Simultaneous Determination of Nitrates and Nitrites in Waters

Abstract

An automatic FIA system for simultaneous determination of nitrates and nitrates in waters is described. The method is based on the classical azodye reaction for nitrites. The sample is split into two flows: (a) one is directly treated with the azodye reagent and sent to the sample flow cell of a double beam spectrophotometer, which gives positive absorbance values, allowing direct determination of nitrites in the sample, (b) the other flow goes through a cadmium reduction microcolumn, where nitrates are reduced to nitrites. The sample is then treated with the azodye reagent and the overall mixture is sent to the reference cell of the same double beam spectrophotometer, which gives negative peaks corresponding to the sum of the absorbances of nitrates and nitrites. Thus deducing the nitrate content in the original sample from the difference. The procedure has been automatized by connecting a digital potentiometer, provided with a RS232C interface, to the register output of the spectrophotometer. The potentiometer is used as a data acquisition interface for an Amstrad 128 microcomputer. A specific program has been developed, allowing: (a) data storage of the successive experiments, (b) data treatment for calculation of the calibration curves and automatic reports of the samples nitrates and nitrites contents.