Supercritical fluid extraction with in situ chiral derivatization for the enantiospecific determination of ibuprofen in urine samples

In situ chiral derivatization was used to obtain diastereomeric amides of i buprofen for their subsequent extraction with supercritical carbon dioxide. For this purpose, ibuprofen [racemic 2-(4-isobutylphenyl)propionic acids] was previously extracted on a C-18 SPE device and quantitatively transferre d into the supercritical fluid extraction (SFE) vessel for derivatization a nd extraction with (R)-1-(naphthen-1-yl)ethylamine as chiral derivatizing b ase, and a mixture of 1-(3-dimethylaminopropyl)-3-ethyl-carbodiimide and 1- hydroxybenzotriazole as reagents, in order to obtain and extract the corres ponding diastereoisomeric amides, which were subsequently determined by liq uid chromatography. The influence of different extraction and derivatizatio n variables (pressure, temperature, extraction time in the static and dynam ic extraction modes, and amount of chiral base) on the extraction efficienc y was studied. Spiked and native urine samples containing ibuprofen were us ed to demonstrate the application of this method. The absolute recovery, se lectivity, precision and accuracy of the combined solid-phase extraction (S PE)/SFE approach were compared to those provided by conventional liquid-liq uid extraction. The results indicated that SFE seems to be an effective cho ice for in situ derivatization since analysis times and solvent consumption were dramatically reduced. (C) 2001 Elsevier Science B.V. All rights reser ved.