Blood Samples and Pharmacokinetic Analysis
Blood samples (2 mL) were then obtained at 0,2,6,12,24,48 and 56 hours after the block injection. The blood samples were centrifuged within 60 minutes after collection. The plasma samples were stored at –20 °C until the assays were performed. The total plasma concentration of ropivacaine was measured by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC‒MS/MS, Waters, American) after direct injection of diluted serum without further cleanup pretreatment. The method and validation characteristics have been described elsewhere [14].