Chemiluminescence of tryptophan and histidine in Ru(bpy)32+-KMnO4 aqueous solution

Amino acids with different chemical structures have different abilities in terms of increasing the intensity of chemiluminescence (CL) of tris(2,2′-bipyridine)ruthenium(II) [Ru(bpy)32+]. In a flow system, CL caused by the reaction between Ru(bpy)33+ and 15 amino acids was observed, but only tryptophan (Trp) and histidine (His) enhanced the intensity obviously, and so the CL of Trp and His and their molecular groups was studied. A calculation of the ionization potentials (IPs) of their N atom indicated that the CL intensities of these compounds depended on their IPs. In addition, the flow system was used for the determination of Trp and His, and the detection limits were 3 × 10−8 mol L−1 for His and 2.5 × 10−9 mol L−1 for Trp. The calibration curves for the two amino acids were 1.0 × 10−7 to 5.0 × 10−3 mol L−1 for His and 1.0 × 10−8 to 1.0 × 10−4 mol L−1 for Trp. The proposed approach was applied to the determination of His in Ganoderma.