Droplet detector for the continuous flow luminol–hydrogen peroxide chemiluminescence system

A droplet detector with high sensitivity and low consumption of reagents and sample for continuous flow chemiluminescence (CL) detection has been developed. The proposed system directly mixes sample with luminescence reagents to form a small droplet, thanks to the gravity force and surface tension of water, in front of a photomultiplier tube (PMT) where the CL reaction takes place. The PMT can then instantaneously record the maximum CL light signal emitted from the whole reaction process. This small droplet can replace the conventional spiral-shaped flow cell for flow injection CL analysis and the droplet detector can reduce interference from the reaction products and residual reagents. To evaluate the potential application of the proposed detector, the CL detection of Fe(II) was assessed under the alkaline luminol–hydrogen peroxide conditions. The CL intensity increased linearly with the concentration of Fe(II) ranging from 10.0 to 1000 nmol dm−3 with a detection limit of 7.16 nmol dm−3 (S/N = 3). The droplet detector allows highly sensitive, stable and fast CL detection of analytes, and thus is promising for application to other analytes having fast CL reaction rates.