Optical sensing of heavy metal ions in anionic micellar solution using a Pd porphyrin phosphorescent probe

Using sodium sulfite as an oxygen scavenger, meso-tetra (4-N,N,N-trimethylanilinium) porphyrin-Pd (Pd-TAPP) emits strong and stable room temperature phosphorescence (RTP) in sodium dodecyl sulfate (SDS) micellar solution. Heavy metal ions, including Fe2+, Co2+, Ni2+ and Cu2+, can efficiently quench the phosphorescence of Pd-TAPP. The Stern–Volmer constants increased in the order Fe2+ < Co2+ < Cu2+ < Ni2+, directly reflecting the relative sensitivity of the method for these ions. The detection limits calculated following the 3σ IUPAC criteria are: 2.3 × 10−7 mol/L for Cu2+, 3.4 × 10−7 mol/L for Co2+, 1.2 × 10−7 mol/L for Ni2+ and 2.1 × 10−6 mol/L for Fe2+. The addition of these ions also resulted in reduction of the lifetime (τ) of Pd-TAPP. The linear relationship between the concentration of Fe2+, Co2+, Ni2+ or Cu2+ ions and τ0/τ indicated the dynamic quenching mechanism.