Determination of Epinephrine in Epinephrine Hydrochloride Injection by Cyclic Voltammetry Based on Glassy Carbon Electrode Modified with Polyornithine

After GCE was polished, cleaned and dried, it was put into phosphate buffer solution (PBS, pH 8.0) containing 1.0×10^-4mol·L^-1 ornithine, with GCE as working electrode, Ag/AgCl electrode as reference and platinum wire electrode as the counter electrode. At the scanning rate of 10 mV·s^-1, the GCE was modified by cyclic voltammetry (CV) in the range of -1.8-2.3 V for 12 segments. The modified electrode was taken out, washed with water and dried, and POrn/GCE was obtained. 0.72 mL of epinephrine (EP) hydrochloride injection (1 mL:1 mg) was taken, diluted to 50 mL with PBS. An aliquot (10 mL) was taken into a 25 mL-small beaker, and stirred for 130 s. CV scanning was performed in three-electrode system with POrn/GCE as the working electrode, the scanning potential was -0.4-1.0 V, and the scanning rate was 0.08 V·s^-1. It was shown that the oxidation/reduction peak potentials (E_pa/E_pc) of EP on POrn/GCE were basically the same as those on GCE, and the oxidation/reduction peak currents (|i_pa|, i_pc) were 39.9, 15.6 μA, which were higher than those (15.3, 1.66 μA) on GCE, and the solvent did not interfere with the determination of EP, indicating that the modified electrode had a better electrocatalytic effect on EP; E_pa had a negative linear relationship with pH, and the absolute value of the slope (0.058 7) of the curve was close to 0.059, indicating that the electrode reaction was a process involving protons, and the number of protons and electrons involved in the reaction was the same; the|i_pa|had a linear relationship with the scanning rate, indicating that the electrode reaction process was controlled by adsorption. Linear relationship between values of concentration and|i_pa|of EP was kept in the range of 2.0-100 μmol·L^-1, with detection limit of 0.13 μmol·L^-1; 100 times of urea, tryptophan, glycine and lysine, 50 times of Cd²⁺ and Ca²⁺, 10 times of Al³⁺ and Fe³⁺ did not interfere with the determination of EP. Repeated analysis of the standard solution with the modified electrode was made 6 times, and RSD of the determined values was 3.9%; the modified electrode was placed 7 d, and|i_pa|only dropped by less than 3.0%. Test for the spiked recovery was carried out on the actual sample, the determined value was basically the same as the label value, and the recovery was found in the range of 97.6%-102%.