Simultaneous determination of manganese and zinc in mixtures using first- and second-derivative spectrophotometry

A new direct spectrophotometric determination of manganese with 5,8-dihydroxy-1,4-naphthoquinone (naphthazarin,NAZA) is reported. Absorption maximum, molar absorptivity and Sandell’s sensitivity of 1:2 (M:L) complex are 695 nm, 1.88×104 l mol−1 cm−1 and 2.92 ng cm−2, respectively. A linear calibration graph is obtained up to a concentration of 7.2 μg ml−1 of manganese. The optimum range for determination (Ringbom) is between 0.20 and 6.8 μg ml−1. A rapid method for simultaneous determination of manganese and zinc in their mixture using derivative spectra is described. The range 0.28–5.6 μg ml−1 manganese could be determined in the presence of 0.33–6.8 μg ml−1 zinc and vice versa. The developed method was applied to the simultaneous spectrophotometric determination of manganese and zinc in some synthetic mixtures and was found to give satisfactory results.