Supercritical fluid extraction combined with solid phase extraction as sample preparation technique for the analysis of β-blockers in serum and urine

A method is developed for the determination of beta-blockers in serum and urine at levels of 0.5 mu g/mL. The technique uses a combination of solid phase extraction (SPE) with in situ derivatization and supercritical fluid extraction (SFE) with subsequent gas chromatography mass spectrometry. The optimization of the SFE step shows that a static extraction period can be eliminated. The method gives good linearity (r = 0.991-0.999) and repeatability in the concentration range of 0.5 to 5 mu g/mL. Relative standard deviations for oxprenolol, propanolol and metoprolol were less than 5% in serum and 5-11% in urine.