Abstract
A novel spot test and a novel chromogenic reagent are reported for thin-layer chromatographic detection and identification of the popular but highly toxic herbicide paraquat. Alkaline phenylhydrazine instantly reduces paraquat to an intense purple radical cation. The reaction is sensitive and highly specific to viologens, i.e., paraquat and diquat herbicide. Surprisingly, 2,4-dinitrophenylhydrazine does not have reaction in this color test. Reaction of the two drugs containing related functional groups is also studied to check whether these drugs also react similarly. Based on this novel color reaction, a simple, ultra-low-cost filter-paper-based sensor is also designed for direct field testing of suspicious forensic samples like vomits and bottle of poison, which are usually found at a crime scene. The possible applications of the reported reaction in the field of organic qualitative analysis, clinical chemistry, and forensic medicine are also discussed.