SPECTROPHOTOMETRIC STUDY OF DICLOFENAC-FE(III) COMPLEX

A multifactor optimisation technique is successfully applied to develo p a new spectrophotometric method in which diclofenac sodium is analys ed and determined as it's Fe(III) complex. The effect of simultaneousl y varying the pH, ionic strength and concentration of colour reagents in the reaction mixture were studied. A four-variable two-level factor ial design was used to investigate the significance of each variable a nd interactions between them. A response surface design was used to op timise complex formation and extraction. It was established that diclo fenac reacts with Fe(III) chloride, in the presence of ammonium thiocy anate, in the pH range 4.2-6.5, forming a red chloroform extractable ( 2:1) complex with maximum absorbance at 481 nm. By applying the method s of Sommer and Job involving non-equimolar solutions the conditional stability constant of the complex, at the optimum pH of 6.0 and an ion ic strength mu = 0.19M, was found to be 10(6.4). Good agreement with B eer's law was found for diclofenac concentrations up to mmol l(-1). Th e nominal percent recovery of diclofenac was 98.8% (n = 10). The lower limit of sensitivity of the method was found to be 14.7 mu g ml(-1). (C) 1997 Elsevier Science B.V.