Spectrophotometry mole ratio and continuous variation experiments with dithizone

Abstract

The well-known color development dithizone reagent, H₂Dz, has been used extensively in trace metal analyses for almost a century. However, very little effort has gone into developing derivatives for aqueous media applications in absence of organic solvents. Synthesis of a suitable (p-COOH)H₂Dz derivative is reported here. For spectrophotometric determinations of various metal (M) to ligand (L) ratio’s in dithizonato metal complexes this reagent provides a versatile alternative for undergraduate chemistry practicals that is cost-effective, yielding repeatable results. The mole-ratio method yield a ratio of 1M : 1L for the silver dithizonate complex and 1M : 3L for cobalt. Employing the continuous variation method give M : L ratio’s of 1 : 3 for both nickel and cobalt. Formation constants are readily calculated from absorbance data. Complete methods, data, calculations and outcomes are reported here. All ratio’s are confirmed by mass spectroscopy.