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(6+) determination based on the double reactions of two metals, Co(2+) with dithizone to form a (DTZ)-Co(2+) complex, and the replacement of Co(2+) in the formed complex with Cr(6+). 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(6+), 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(2+) was also applied as a microwell plate film. In the presence of Cr(6+), the colour of DTZ-Co(2+) changed from red to magenta. Among the three studied methods, the colorimetric DTZ-Co(2+)/PU-NF presented the best results. Its linearity range was 0.001–1.0 mg L(−1), with a regression equation of Cr(6+) = −0.189 + (0.0056 × red) + (0.0086 × green) − (0.0129 × blue), R(2) of 0.990. The limit of detection was 0.001 mg L(−1) and the precision was 1.7%. The applicability of DTZ/PU-NF was validated for Cr(6+) 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(2+)/PU-NF and DTZ-Co(2+)/PU-MPF proved to be highly selective, rapid, user-friendly, simple and reliable.