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 (Co²⁺) 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 Co²⁺. The procedure allowed the linear detection of Co²⁺ 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 Co²⁺ solution. The method was successfully applied to the determination of Co²⁺ in blue silica gel samples.