Biodegradable asparagine–graphene oxide free chlorine sensors fabricated using solution-based processing

A free chlorine-sensing biodegradable ink was made by functionalizing asparagine onto graphene oxide then deposited on an electrode. The sensor showed a sensitivity of 0.30 μA ppm−1, selectivity amid interfering ions, and low temperature dependence.

Simple-to-use and portable device for free chlorine determination based on microwave-assisted synthesized carbon dots and smartphone images

A new portable and simple 3D printed device was designed for free chlorine determination in water samples. The analytical method was based on the quenching caused by free chlorine on the fluorescence emission of the carbon dots (CD) synthesized from citric acid and urea. The fluorescence was captured through the camera of a smartphone, which was coupled to the 3D printed device, and the images were processed using the RGB system by the ImageJ 1.51q software. The proposed method was selective and precise (RSD% 4.6, for n = 6), and the trueness of the results was evaluated by comparing the results obtained with those recovered by the spectrophotometric method 4500-Cl G (standard method), with good agreement between them. Moreover, the remarkable correlation between the CD signal and the free chlorine concentration resulted in a determination with low detection limits (limit of detection of 6 μg L^-1 and limit of quantification of 20 μg L^-1). Therefore, the new method and the related portable device could be considered a fast, economical and reliable alternative for the on-site determination of free chlorine in water samples.

Field analysis of Cr(vi) in water samples by using a smartphone-based ultralong absorption path reflection colorimetric device

Hexavalent chromium is highly toxic and regarded as one of the main pollutants in the environment. A multiple reflection colorimetric cell is designed to improve the sensitivity in field analysis for Cr(vi).