Experimental design applied to a spectrophotometric study of a diclofenac sodium–copper(II) complex

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Abstract
An extraction method with spectrophotometric detection for the determination of diclofenac sodium, using copper(II) acetate as the analytical reagent has been established, with the aid of two statistical optimization procedures. A three-variable, two-level full factorial design was used to estimate the effects of varying the pH, ionic strength (I) and concentration of copper(II) acetate in the reaction mixture, in addition to the interaction between them. A response surface diagram was used to optimize the experimental conditions for the complex formation and extraction. It was found that diclofenac sodium reacts with copper(II) acetate, in the pH range 4.4–6.4, to form a green chloroform-extractable complex with a molar ratio of diclofenac sodium to CuII of 2:1 and with a maximum absorbance at 480 nm. The relative stability constant of the complex, at the optimum pH of 6.0 and I of 0.18 mol dm–3, was found to be 106.8. Good agreement with Beer's law was found for diclofenac sodium concentrations of up to 6.29 mmol dm–3, calculated for the final solution, with a detection limit of 72 µg ml–1. The nominal recovery of diclofenac sodium was 98.5%(n= 10).

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