SUPERCRITICAL-FLUID EXTRACTION OF CLEVIDIPINE FROM A WATER-BASED VEGETABLE OIL EMULSION

A method was developed for the determination of clevidipine and some o f its degradation products from a water based soya bean oil emulsion u sing supercritical fluid extraction (SFE). A trap packed with octadecy l silica (ODS) and stainless steel beads (ss) in the proportions 1:4 ( v/v), with ODS closest to the restrictor, offered adequate trapping an d recollection performance. The extractability of clevidipine (standar d solution) was investigated using different sample support materials (hydromatrix, sea sand, filter paper, glass beads, and ss beads). Inte ractions were very small for ss beads but considerably stronger for, e .g., filter paper. On ss beads clevidipine could be extracted within a relatively short time (24 min) using mild conditions (91 bar, 0.50 g/ mL, 4 mL/min, 40 degrees C, 3% methanol, 25 thimble volumes swept). Fi lter paper required harsher extraction conditions (134 bar, 0.75 g/mL, 5% methanol, 40 degrees C) to break interactions between clevidipine and the paper. However, filter paper gave a better distribution of the emulsion on the sample support than the more inert stainless steel be ads. This resulted in higher recoveries (102% compared to 63% using st eel beads) and better precision in the quantitative measurements of em ulsion samples with a repeatability of 1.8% (RSD; n=8) for filter pape r compared to 7.4% (RSD; n=8) for ss beads. Thus, filter paper was rec ommended for quantitative determination of clevidipine in emulsion sam ples. No degradation product of clevidipine could be found in the emul sion matrix. In order to detect the degradation products at least 3 mt emulsion has to be extracted to reach the limit of detection. At pres ent such large volumes can not be sustained in the extraction thimble. The current maximum volume to be extracted is I mL.