Fluorescein and its derivatives: New coreactants for luminol chemiluminescence reaction and its application for sensitive detection of cobalt ion

Fluorescein and its derivatives, including 4′,5′–dibromofluorescein, 2′,7′–dichlorofluorescein and 2′,4′,5′,7′–tetrabromofluorescein can be employed as efficient coreactants for luminol reaction. Under an alkaline condition they reacted with luminol to produce measureable chemiluminescence (CL) in the absence of any extra–oxidant. Cobalt ion (Co 2+ ) significantly enhanced the CL emission of the reaction. The CL emission was strongly dependent on the concentration of carbonate buffer used; higher concentration of carbonate buffer provided more intense CL emission. The system had two emission peaks locating at 425 nm and 535 nm, respectively. With 4′,5′–dibromofluorescein as the coreactant for luminol reaction, a new CL method was developed for the detection of Co 2+ . The procedure allowed the linear detection of Co 2+ in the range of 5–1000 nmol/L. The limit of detection (LOD) and limit of quantitation (LOQ) were 1.8 nmol/L and 5.0 nmol/L, respectively. The intra–day precision (n = 11) and inter–day precision (n = 3) was 3.2% and 4.7% for replicated measurements of 0.2 μmol/L Co 2+ solution. The method was successfully applied to the determination of Co 2+ in blue silica gel samples.