Abstract: A new method was established to determine tryptophan and tyrosine in four edible plants wildly grown in Zhengzhou region, Sonchus asper, Plantago asiatica, Vigna minima and Pyracantha fortuneana. Samples were hydrolyzed with with 6 mol/L sodium hydroxide solution determined by molecular fluorescence spectrometry. The average contents of tryptophan and tyrosine in the wild plants were 1.37–2.63 mg/g and 7.98–25.83 mg/g, respectively, with a relative standard deviation equal to or less than 5.4% (n = 5). The proposed tryptophan standard curve showed good linear relationship over the concentration range of 0.00–0.10 μg/mL. The method exhibited a limit of detection of 0.011 μg/mL and 0.033 μg/mL and a limit of quantification of 0.037 μg/mL and 0.11 μg/mL for tryptophan and tyrosine, respectively. The propose tyrosine standard curve displayed a linear range of 0.0–1.0 μg/mL. The average spike recovery rates of tryptophan and tyrosine in these four plants were 93.5%–105% and 94.6%–100.5%, respectively. This method was simple, sensitive, rapid, and suitable for practical applications.

Key words: molecular fluorescence spectrometry, tryptophan, tyrosine, Sonchus asper, Plantago asiatica, Vigna minima, Pyracantha fortuneana