Use of a digital image in flow analysis: Determination of nitrite and nitrate in natural waters

Abstract

A webcam is proposed as the detector in a flow system with multicommutation, and the feasibility of the approach is demonstrated in the determination of nitrate and nitrite in natural waters. The typical transient signal inherent to the flow system was obtained using a digital video and quantified by ImageJ software. The linear dynamics range for nitrite and nitrate determinations were 0.2 to 2.0 mg L-1 NO2 - and 1.0 to 10.0 mg L-1 NO3 -, with relative standard deviation < 2% for both analytes. The limits of detection were 0.01 and 0.04 mg L-1 for nitrite for nitrate, respectively, and the sampling rate were 80 and 103 h-1 for nitrite and nitrate, respectively. The use of webcams has a high potential for analysis in the visible region of the electromagnetic spectrum, and the proposed strategy constitutes a promising alternative to traditional absorbance measurements that depend on conventional equipment. The webcam detection system is attractive, especially in relation to field analysis.