Spectrophotometry mole ratio and continuous variation experiments with dithizone

  • Lumanyano L.A. Ntoi
  • Karel G. von Eschwege


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.


Journal Identifiers

print ISSN: 2227-5835