3‐Hydroxy‐2‐[1′‐phenyl‐3′‐(p‐chlorophenyl)‐4′‐pyrazolyl]‐4‐oxo‐4H‐1‐benzopyran as a spectrophotometric reagent for trace determination of tungsten(vi)

3‐Hydroxy‐2‐[1′‐phenyl‐3′‐(p‐chlorophenyl)‐4′‐pyrazolyl]‐4‐oxo‐4H‐1‐benzopyran solution in acetone forms a yellow‐coloured complex with tungsten(vi ) in perchloric acid medium which is extractable into chloroform after equilibration. In this study, tests were carried out on this compound and it was found to be quite stable and to obey Beer’s law. Interactions with various ions were studied and the molar absorptivity, Sandell’s sensitivity and relative standard deviation were also investigated. Job’s method, the mole ratio method and the equilibrium‐shift method were also used. The ratio of metal to ligand was measured using a method that was simpler, more accurate, sensitive, rapid and selective as compared with existing methods. This method is applicable to the analysis of various samples of varied composition.