Fig 2. Absorbance spectra obtained by the UV spectrophotometer.

(A) Spectra of four kinds of acid buffer, (B) spectra of all reagents. (C, E) spectra of standard samples from 1 μg mL⁻¹ to 100 μg mL⁻¹ before heating, (D, F) the absorption spectra of standard samples from 1 μg mL⁻¹ to 100 μg mL⁻¹ after heating.