A novel double metal-dithizone functionalized polyurethane electrospun nanofiber and film for colorimetric determination of hexavalent chromium.

This work proposes a highly specific method of Cr determination based on the double reactions of two metals, Co with dithizone to form a (DTZ)-Co complex, and the replacement of Co in the formed complex with Cr. The fast degradation of DTZ in solution in wet analysis was overcome by preparing dithizone functionalized polyurethane nanofibers that were electrospun into a membrane (DTZ/PU-NF) and a microwell plate film (DTZ/PU-MPF). For comparison, the performance of diphenylcarbazide (DPC), a currently used complexing agent for Cr, was also investigated. Colour changes were detected as red-green-blue values. The DTZ/PU-NF was smooth, with an average diameter of 384.09 nm and no bead appeared. A dense network structure was formed. The best formulation of DTZ, PU and Co was also applied as a microwell plate film. In the presence of Cr, the colour of DTZ-Co changed from red to magenta. Among the three studied methods, the colorimetric DTZ-Co/PU-NF presented the best results. Its linearity range was 0.001-1.0 mg L, with a regression equation of Cr = -0.189 + (0.0056 × red) + (0.0086 × green) - (0.0129 × blue), of 0.990. The limit of detection was 0.001 mg L and the precision was 1.7%. The applicability of DTZ/PU-NF was validated for Cr in vegetable oils with recoveries of 89.5-116.8%. The sensitivity of DTZ/PU-NF was ten times higher than that of DTZ/PU-MPF. The methods based on DTZ-Co/PU-NF and DTZ-Co/PU-MPF proved to be highly selective, rapid, user-friendly, simple and reliable.