Materials
Ropivacaine was obtained from Libang Pharmaceutical Co., Ltd., China. The purity was 99%. Benzyl alcohol and benzyl benzoate were purchased from Hunan Er-kang Pharmaceutical Co., Ltd., China. Soybean oil was produced by Tieling Pharmaceutical Co., Ltd., China. Ropivacaine hydrochloride injection (RHI) was manufactured by AstraZeneca AB, Sweden. The specifications are 100 mg:10 mL. RODD was composed of 2% ropivacaine, 4% benzyl alcohol, 30% benzyl benzoate and approximately 64% soybean oil and was commissioned to be produced at the GMP (Good Manufacturing Practice)-certified plant of Jiangsu Taikang Biomedical Co., Ltd, batch number CR20191001. Ropivacaine-D7, a reference substance, was obtained from the United States Pharmacopoeia.