MODULATED POTENTIAL ELECTROGENERATED CHEMILUMINESCENCE OF LUMINOL AND RU(BPY)3(2+)

Chemiluminescence emission intensity is modulated by modulating the potential of a working electrode which is used to generate a key species in the electrogenerated chemiluminescence (ECL) reaction. The emission is monitored synchronously using a lock-in amplifier. The reactions used in the characterization are luminol with hydrogen peroxide and tris(2,2'-bipyridyl)ruthenium (II) (or Ru(bpy)3(2+)) with oxalate. Modulation widths of +/- 50 mV yield maximum signals for luminol when centered at 0.45 V (vs Ag/AgCl) and for Ru(bpy)3(2+) when centered at 1.05 V. The resulting signal decreases with increasing modulation frequency and shows that luminol/H2O2 is a faster ECL system than Ru(bpy)3(2+)/oxalate. Working curves for luminol and for oxalate have essentially the same linear range and slope with the modulated potential approach as with a DC electrode potential. This approach provides capability for differentiating the analytical signal from constant background emission or stray light.