Determination of tetracaine hydrochloride by fluorescence quenching method with some aromatic amino acids as probes.

A novel fluorescence quenching method for the determination of tetracaine hydrochloride (TA·HCl) concentration with some aromatic amino acids as fluorescence probe has been developed. In pH 6.3 acidic medium, tryptophane (Trp), tyrosine (Tyr) or phenylalanine (Phe) can react with tetracaine hydrochloride to form an ion-association complex by electrostatic attraction, aromatic stacking interaction and Van der Waals' force, which lead to fluorescence quenching of above amino acids. The maximum fluorescence excitation and emission wavelengths of them are located at 278, 274, 258 nm and 354, 306, 285 nm, respectively. The relative fluorescence intensity (F (0)/F) is proportional to the TA·HCl concentration in certain range. The linear ranges and detection limits are 1.2-5.0 μg/mL and 0.37 μg/mL for Tyr-TA·HCl system, 1.3-6.0 μg/mL and 0.38 μg/mL for Trp-TA·HCl system, and 1.4-6.0 μg/mL and 0.41 μg/mL for Phe-TA·HCl system. The optimum reaction conditions, influencing factors and the effect of coexisting substances are investigated. And the results show the method has a good selectivity. Judging from the effect of temperature, the Stern-Volmer plots and fluorescence lifetime determination, the quenching of fluorescence of amino acids by TA·HCl is a static quenching process.