Determination of Sunset Yellow in Mineral Water and Beverage by Fluorescence Spectroscopy with Copper Nanoclusters as Probe

Copper nanoclusters (CuNCs) were prepared using one-step wet chemical synthesis method, and a method for the determination of sunset yellow in mineral water and beverage by fluorescence spectroscopy was proposed using CuNCs as fluorescent probe. The mixture containing 15.0 mL of water, 4.0 mL of 0.01 mol·L^-1 L-cysteine solution and 0.2 mL of 0.1 mol·L^-1 copper nitrate solution was placed in 15 ℃ water bath and stirred for 5 min. Then 1.00 mL of 1.0 mol·L^-1 sodium hydroxide solution was added slowly, and the reaction was continued for 2.5h in 15 ℃ water bath. The light blue solution of CuNCs protected by L-cysteine was dialyzed for 72 h, and dried at 60 ℃ for 72h to obtain CuNCs. An aliquot of 50 μL filtered sample was mixed with 0.5 mL of 0.33 g·L^-1 CuNCs solution, and diluted to 3.0 mL with Burritan-Robinson buffer (pH 8.0). The excitation wavelength was set as 370 nm, and the slit widths of excitation and emission were set as 5, 10 nm, respectively. The fluorescence intensities of the system at 490 nm before and after CuNCs addition were recorded. The results showed that the fluorescence of CuNCs was quenched by sunset yellow mainly coming from inner filter effect. Linear relationship between fluorcescence intensity ratio (F/F₀) of the system and concentration of sunset yellow was kept in the range of 2.00-60.00 μmol·L^-1, and the detection limit (3s/k) was 1.31 μmol·L^-1. The recoveries of sunset yellow in mineral water and beverage were in the range of 95.2%-104%, and RSDs (n=5) of the determined values were in the range of 2.0%-3.7%.