Disposable Pipette Extraction Phase Based on Styrene-Divinylbenzene/Pernigraniline Composite, Applied for Dexamethasone Determination in Synovial Fluid by HPLC with UV Detector

A reliable method using disposable pipette extraction (DPX) based on composite of pernigraniline and styrene-divinylbenzene (Sty-DVB) copolymer was applied to the analysis of dexamethasone in synovial fluid using high-performance liquid chromatography and ultraviolet (UV) detector (HPLC-UV). DPX variables, namely, number of draw/eject cycles for extraction or desorption, sample pH, volume, and desorption solvent, were optimized to establish the best sorption equilibrium and analysis time. The highest extraction efficiency value was obtained with 50 mu L of synovial fluid mixed with 1950 mu L of water, in five cycles of 300 mu L of sampling, followed by liquid desorption of the drug with 300 mu L of methanol in three cycles. The developed method demonstrated a linear response over the range from 10 to 100 ng/mL, with R-2 = 0.993. The limit of quantification (LOQ) was 10 ng/mL. Based on the validation results, the proposed method can be a useful tool to detect dexamethasone levels in synovial fluid.