[Fluorescence spectra and fluorescence quantum yield of sulfosalicylic acid]

Fluorescence spectra and fluorescence quantum yield of sulfosalicylic acid (SSA) have been studied. Under the condition of pH<2, SSA has no fluorescence. With the increase in pH value, fluorescence intensity of SSA increases. In the range of pH 5-10.5, SSA gives a strong and steady fluorescence with a maximum emission wavelength at 402 nm and excitation wavelengths at 212, 238 and 297 nm, respectively. In strong alkaline solutions with pH>13, SSA exists as another fluorescence species with a maximum excitation wavelength at 261 nm and a maximum emission wavelength at 390 nm. The excitation spectrum of SSA changes when its concentration is relatively higher, but the emission spectrum remains unchanged. There is an excellent linear relationship between fluorescence intensity and the concentration of SSA under neutral condition. The linear range is 5-250 ng x mL(-1), and the detection limit is 5 ng x mL(-1). Using quinine bisulphate as a reference, fluorescence quantum yields of SSA at different wavelengths were measured. At the maximum excitation wavelength 297 nm, fluorescence quantum yield of SSA is 0.54.