Spectrophotometric determination of copper with α, β, γ, δ-tetraphenylporphine trisulfonate

Water-soluble porphyrin, α, β, γ, δ-tetraphenylphorphine trisulfonate (TPPS, H₂R), was found to be a very useful agent for both the direct spectrophotometric determination and the photometric titration of copper(II). The molar absorptivity of H₄R²⁺ at 434 nm is 5.0·10⁵ and the spectrophotometric sensitivity is 0.00013 μg Cu cm^?2 for A=0.001. Beer's law is followed in the range 0.006 μg–0.06 μg Cu ml^?1. Among twenty-two elements examined, only zinc(II) seriously interfered. Acid dissociation constants and salt effects on the spectra of TPPS were evaluated.