Liquid chromatographic sample cleanup coupled on-line with gas chromatography in the analysis of beta-blockers in human serum and urine

An on-line coupled reversed-phase liquid chromatographic-gas chromatographic (LC-GC) method with minimal manual sample preparation is developed for the analysis of metoprolol, oxprenolol, propranolol, timolol, and codeine (as an internal standard) in human serum and urine. The method is based on a loop-type interface and concurrent eluent evaporation technique. On-line liquid-liquid extraction (LLE) is used to extract the analytes from aqueous eluent to organic solvent before injection onto the GC, and the two phases are separated with a sandwich-type phase separator. The LC is used for cleanup, and the GC is used for the final separation and detection of the analytes. Total analysis time is less than 45 min, which is much less than those of traditional analysis methods. Recoveries in LC cleanup and on-line LLE are excellent. A marked increase in the recoveries with on-line LLE is obtained by heating the aqueous eluent and the extraction coil. Linearity and repeatability of the method are good or both serum and urine, and the limits of quantitation for the analytes are 18-44 ng/mL.