Spectrophotometric determination of manganese with derivatives of 1,3,3-trimethyl-2-[3-(1,3,3-trimethyl-1,3-H-indol-2-ylidene)propenyl]-3H-indolium

Abstract

A new, simple, rapid, and sensitive spectrophotometric method has been developed for the determination of manganese in sewage. The method is based on the reaction of manganese with derivatives of 1,3,3-trimethyl-2-[3-(1,3,3-trimethyl-1,3-H-indol-2-ylidene)propenyl]-3H-indolium to form a colored ion associate with a sensitive absorption maximum at 560 nm. The appropriate reaction conditions have been established: pH 8.5–10.0, 1.25–2.3×10⁻³ mol L⁻¹ 1-nitroso-2-naphthol, and 1.6–2.4×10⁻⁴ mol L⁻¹ dye reagent. Beer's law is obeyed for manganese concentrations up to 4.2 mg L⁻¹. The limit of detection is 0.01 mg L⁻¹ Mn²⁺; the molar absorptivity of the ion associate was 7.5×10⁴ L mol⁻¹ cm⁻¹. The effect of various foreign ions was examined. A reaction mechanism is suggested. The developed procedure was tested for determination of manganese in sewage with satisfactory precision and accuracy.