All reagents used were of analytical grade, all purchased from Merck and used without further purification.
Distilled water was obtained from a glass double-distiller and used to prepare all solutions. Stock solution of Cr (III)
and Fe (III) were prepared by dissolving appropriate amount of K2Cr2O7 and Fe(NO3)3•9H2O, respectively.
Quantitative analysis was conducted using colorimetric reagent of 1,5-diphenylcarbazide (DPC) for Cr (III) and
potassium thiocyanate (KSCN) for Fe (III).