Cathodic electrochemiluminescence of meso-tetra(4-carboxyphenyl) porphyrin/potassium peroxydisulfate system in aqueous media

• It is found for the first time that water-soluble TCPP could produce cathodic ECL.
• A novel and simple determination method for prophyrin is proposed.
• This way can be used to detect pheophorbide obtained from fresh vegetables.

A two-step cathodic electrochemiluminescence (ECL) of meso-tetra(4-carboxyphenyl) porphyrin (TCPP) in aqueous solution has been reported for the first time. ECL generates upon sweeping from -0.2 V to -1.5 V using potassium peroxydisulfate (K2S2O8) as a reductive–oxidative coreactant. Two cathodic ECL peaks are found simultaneously. One appears at -0.8 V which is corresponding to the reduction of TCPP, another is at -1.1 V that is attributed to the reduction of K2S2O8. ECL efficiency (φecl) is 0.22 for TCPP using Ru(bpy)32+/S2O82− as the standard (φecl = 1). Under the optimum conditions, ECL intensity has a linear relationship with the concentration of TCPP in the range of 2.0 × 10−7 to 1.0 × 10−5 mol L−1 with the detection limit of 1.7 × 10−8 mol L−1. The practical application to determination pheophorbide which is obtained from fresh spinach leaves has been accomplished. The results demonstrate the facility and effectivity of our method for quantitative analysis of porphyrin. At the same time of building this method, the possible ECL mechanism is discussed in detail.