Effect of different conditions on the extraction yields of forsythiaside A, rutin and phillyrin when acetic acid was added to the solvent. The value of forsythiaside A is shown on the secondary y-axis on the right. Condition 1: 50% ethanol as solvent, ultrasonic power 200 W, temperature 30 °C; Condition 2: 50% ethanol + 2% acetic acid as solvent, ultrasonic power 200 W, temperature 30 °C; Condition 3: 50% ethanol + 5% acetic acid as solvent, ultrasonic power 200 W, temperature 30 °C; Condition 4: 50% ethanol + 5% acetic acid as solvent, ultrasonic power 200 W, temperature 50 °C; Condition 5: 50% ethanol + 5% acetic acid as solvent, ultrasonic power 100 W, temperature 30 °C.