Study on the Effect of pH on Luminol Chemiluminescence Reaction

Abstract

Chemiluminescence refers to a distinctive physical‑chemical phenomenon where chemical energy released by chemical reactions is directly converted into light energy without thermal radiation.^[1] Benefiting from high sensitivity, fast response and simple testing conditions, chemiluminescence has been widely applied in forensic identification, biochemical sensing and environmental analysis. ^[2]The luminol‑potassium ferricyanide‑hydrogen peroxide system is one of the most classic and representative chemiluminescence reaction models^[3]. The luminescence performance of this system is highly susceptible to the pH of reaction medium^[4]. In this experiment, the dosages of luminol, potassium ferricyanide and hydrogen peroxide were kept as constant controlled variables. Sodium hydroxide solid was applied to adjust the alkalinity of reaction solution. A series of pH gradients including pH 12, pH 13, pH 13‑14, pH 14 and pH 14.5 were constructed. All experimental observations were completed under dark conditions. Luminescence phenomena, relative brightness and total luminescence duration were carefully recorded for each experimental group.Experimental results demonstrated that no observable luminescence occurred at pH 12. pH 13 turned out to be the optimum reaction condition: the system emitted stable, bright blue chemiluminescence with the maximum luminescence duration of 45 seconds. When pH value exceeded 13, initial luminescence brightness still maintained at a relatively high level, yet luminescence duration decreased sharply as alkalinity further increased. This set of experiments verifies that pH acts as a decisive regulatory factor for both the triggering process and overall performance of luminol‑based chemiluminescence reactions. Accurate pH control is essential for practical chemiluminescence detection work^[5].