Esterase inhibitor screen: As is shown in TABLE 1, different inhibitors inhibit the degradation of clevidipine to different extent.The most efficient inhibitor is 4％ citric acid, followed by TTFA, BNPP, and PMSF.The weakest inhibitor is NaF.In general, the degradation of an analyte in biological matrix is significantly slower when the sample is processed on ice (～4 ℃) compared with at room temperature.