Analytical Use of Luminescence Induced Ultrasonically in Solution. I. Sonic Chemiluminescence of Luminol for Determination of Cobalt(II) at Sub-pg Levels by Flow Injection and Continuous Flow Methods

Ultrasonic irradiation of alkaline luminol solution produces intense light emission (sonic chemiluminescence) as a result of the reaction of luminol with reactive species which are generated ultrasonically from water molecule. For the analytical application of ultrasound-induced luminescence, the sonic chemiluminescence of luminol is first utilized for the determination of ultratraces of cobalt(II) by flow injection and continuous flow methods. This novel method is based on the measurement of sonic chemiluminescence enhanced by the presence of cobalt(II); it provides analytical characteristics comparable to those for the conventional luminol chemiluminescence method using hydrogen peroxide as an oxidizing agent. The limit of detection is 0.06 pg(10-μl sample injection) or 0.06 pg ml−1 (continuous sample flow), the linear dynamic range is 3 orders of magnitude (10-μl sample injection), the sampling rate is 120 h−1, and the relative standard deviation is 3.9% for 6 pg Co(II) (n=10). The method is successfully applied to real samples. Possible explanation of sonic chemiluminescence is also presented; the mechanism involving superoxide anion radical is proposed for the cobalt(II)-catalyzed sonic chemiluminescence.