Development of a Simple and Sensitive Terbium Sensitized Fluorescence Method for Determination of Epinephrine and Norepinephrine in Serum

A simple, rapid, selective and highly sensitive fluorimetric method for determination of two catecholamines, i.e. norepinephrine (NE) and epinephrine (EP), in serum samples was developed. The method is based on the fluorescence sensitization of terbium (Tb3+) by complexation with both catecholamines in the presence of lanthanum (La3+), as a co-cation, and in a Na2SO3 solution (chemical deoxygenating agent), which fluoresces intensely with an emission maximum at 545 nm when excited at 312 nm. We found that fluorescence enhancement effects were observed when La3+ was added to the system (co-luminescence effect). In the presence of this element the fluorescence of the Tb-catecholamines system was enhanced by a factor of about 15 compared with that of the system without La3+. Optimum conditions for the formation of the complexes were investigated. Under optimum conditions, a linear relationship was obtained between the fluorescence intensity and catecholamines concentration in the range of 2.5×10-3 to 0.22 μg.ml- 1. The detection limits were 0.59 and 0.58 μg.l-1 for EP and NE, respectively. Relative standard deviation (RSD) values for two compounds were in the range of 1.2-2.1% indicating excellent reproducibility. The proposed method was successfully applied to the determination of EP and NE in spiked serum samples after deproteinization of the samples with acetonitrile. Analytical recoveries from treated serum samples were in the range of 95-105%.