Used as a sensitive analytical reagent for the colorimetric detection of metal ions, particularly mercury (Hg²⁺) and copper (Cu²⁺). It forms highly colored complexes with these metals, allowing for visual or spectrophotometric determination at trace levels. Commonly applied in environmental monitoring for testing water and soil samples due to its high selectivity and distinct color change upon complexation. Also utilized in the development of test strips and sensors where rapid, on-site detection is required. Its stability in solid form and in solution makes it suitable for incorporation into commercial kits for metal analysis.