Simultaneous determination of benzoic acid and saccharin in soft drinks byusing lanthanide-sensitized luminescence

A simple and fast approach is used for the first time to develop a time res olved lanthanide-sensitized luminescence method for the simultaneous determ ination of a preservative and a sweetener, namely benzoic acid (BZ) and sac charin (SC), respectively, in food samples. The method involves the formati on of the corresponding ternary chelates with terbium(III) and trioctylphos phine oxide (TOPO) in the presence of Triton X-100, and the measurement of the initial rate and equilibrium signal of this system, which were obtained in 0.1 and 5 s, respectively. The dynamic ranges of the calibration graphs , obtained by using kinetic and equilibrium measurements, were 0.2-36 mu g ml(-1) and 0.15-30 mu g ml(-1), respectively, for BZ, and 3.3-24 mu g ml(-1 ) and 4-36 mu g ml(-1) for SC and the detection limits were 0.07 and 0.04 m u g ml(-1), respectively, for BZ, and 1.1 and 1.2 mu g ml(-1), respectively , for sodium SC. The relative standard deviation ranged between 2.3 and 3.0 %; Both compounds were determined simultaneously by using a system of two e quations which were resolved by using the calibration data obtained individ ually for each analyte and by multiple linear regression. Mixtures of BZ an d SC in ratios between 3:1 and 1:9 were satisfactorily resolved by using bo th approaches. The method was applied to the direct analysis of several sof t drinks. Analytical recoveries ranged between 89.3 and 108.5%.