![]() The selected concentration was 0.4 mM, the first value in the plateau. The results showed that the CL signal increased as sodium hypochlorite concentration increased. The light intensity was recorded at 10 s also. Second, the sodium hypochlorite concentration was kept constant (0.248 mM) and the luminol concentrations were varied between 0.05 mM and 0.5 mM ( Figure 3). Moreover, it was important that the CL signal is not highly dependent on luminol concentration, thus 0.248 mM was selected. It was interesting to reach the maximum signal of the luminometer without saturation in order to obtain the maximum working range for the analyte, due to the fact that the presence of the analyte decreases the CL signal. As shown in Figure 3, it was found that the CL signal increased as the sodium hypochlorite concentration increased too. The light intensity, a transient signal, was recorded at 10 s, which was the minimum time needed for measuring precisely in the portable instrument and achieving low detection limits. First, the luminol concentration was kept constant (0.4 mM) and the sodium hypochlorite concentrations were varied between 0.025 mM and 0.4 mM. To establish the optimal conditions for organic amino nitrogen and ammonium determination, the effect of luminol and sodium hypochlorite concentration on CL intensity of the formed compound was previously studied in solution using the portable luminometer. This sensor allows in situ monitoring owing to its simplicity, rapidity, and portability. ![]() The achieved limit of detection was around 10 µg ![]() This portable method was successfully validated and applied to the analysis of several real waters: fountain, river transition, lagoon, and seawater with recovery values between 92% and 112%, which indicated that the matrix effect was absent. The liberation of the luminol from sensor is higher than 90% and the sensor is stable for at least a week at room temperature. Then, the remaining hypochlorite reacts with luminol sensor by producing a luminescence signal, which was measured by using a portable luminometer, being inversely proportional to nitrogen concentration. The method is based on the reaction between amino nitrogen compounds and hypochlorite to produce chloramino derivatives. We propose a portable sensor, obtained by embedding luminol into the tetraethylorthosilicate/trietoxymethylsilane (TEOS/MTEOS) composite, for the quantitative determination of organic amino nitrogen and ammonium in water with the goal of achieving low levels of concentration.
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