Optical sensing of sulfite with a phosphorescent probe Original Research Article

Spectral-luminescent properties and quenching behavior of the covalent conjugate of the platinum(II) complex of coproporphyrin-I and bovine serum albumin (PtCP–BSA) was investigated. Quenching of phosphorescence by sulfite was studied in detail in an acidic range as a function of pH. Strong dynamic quenching of the phosphorescence by sulfite occurred at pH below 4.0 which was attributed to the formation of sulfur dioxide. The quenching reached its maximal level at pH below 1.5, Stern–Volmer quenching constants being as high as 2000 M−1. A new flow-injection system for the determination of sulfite was developed based on the PtCP–BSA conjugate immobilized on a preactivated Biodyne ABC membrane and placed in a flow-cell, with an acidic carrier buffer and fiber-optic phosphorescent detector. Such a solid-state phosphorescent probe is quenchable by sulfite and allowed rapid on-line detection of sulfite with a detection limit of about 10 μM. Performance of the new system and possible interferences were investigated.