A palm-sized wireless device for colorimetric nitrite determination in water

Abstract

In this work a palm-sized, affordable, and wireless device is presented for colorimetric determination of nitrite in water, based on the Griess method. A RGB sensor APDS 9960 was used, as a detector, to determine the amount of nitrite in water and the color intensity of the dye produced by the reaction between nitrite and Griess reagent was detected. The detection system consisted of a green LED (λmax = 530 nm) used as light source and the signals were monitored by selecting the green channel. An ESP32 board was used for signal processing and this ESP board includes a housing having space for receiving a lithium-ion battery, used for the power source of the circuit. Also, this boards act like a router which was employed to transfer data between the devices. A detection limit of 2 μgL−1 (3σ) was achieved by the proposed procedure with a relative standard deviation value varied from 1.6 to 2.5 for intra-day (and from 2.4 to 2.7 for inter-day precision, when a Green and White LEDs were used, respectively. With a low reagent demand of 20 μL, the proposed device is environmentally friendly, ideal for in situ determination and the resulting battery life of a 7-hours is feasibly for nitrite monitoring in different water samples. A comparison between the presented procedure employing a white and a green LEDs, used as light source, was conducted for nitrite determination and the results were compared with those obtained by UV–vis. The proposed procedure employing the green LED was more sensitive and provides greater accuracy.