Spectrophotometric quantification of the salicylanilide anthelmintic rafoxanide based on the charge-transfer absorbance of its iron(III) complex

Abstract

Formation of an iron(III)—rafoxanide chelate provides the basis for a direct spectrophotometric method for the quantification of this halogenated salicylanilide in the concentration range 9.00 × 10 -4–7.00 × 10 -3 M. The intense visible charge-transfer absorption band of the complex at 505 nm represents a general spectrophotometric characteristic that is useful for other substituted salicylanilides. The maximum absorption wavelength of the charge-transfer band shifts monotonically to higher energy in an order consistent with Hammett substituent constants.