Efficient molecularly imprinted polymer as a pipette-tip solid-phase sorbent for determination of carvedilol enantiomers in human urine

In this work, an efficient pipette tip based on molecularly imprinted polymers solid-phase extraction (PT-MIP-SPE) method was developed for carvedilol (CAR) analysis. This compound is available in clinical practice as a racemic mixture, in which (-)-(S)-CAR is a beta- and alpha(1)-adrenergic antagonist, while ( +)-(R)-CAR only acts as an alpha(1)-adrenergic antagonist. Enantioseparation of CAR presented satisfactory retention times (5.85 and 14.84 min), acceptable theoretical plates (N = 2048 and 2018) and good resolution (Rs = 9.27). The separation was performed using a Chiralpak (R) IA column (100 mm x 4.6 mm, 3 mu m), a mixture of methano-I:ethanol:water (64:15:21, v/v/v) plus 0.3% diethylamine as mobile phase, temperature of 35 degrees C and flow rate of 1.5 mL min(-1). After density functional theory calculations based on prepolymerization complexes, the best protocol for the MIP synthesis was chosen. Then, some parameters that affect the PT-MIP-SPE technique were investigated. After optimization, the best conditions were 300 [11, of water as washing solvent, 500 I, of acetonitrile:acetic acid (7:3, v/v) as eluting solvent, 20 mg of MIP, 500 mu L of urine sample (pH 12.5) and no addition of NaCl. Recoveries relative standard deviation (RSD%) for ( +)-(R)-CAR and (-)-(S)-CAR were 101.9 +/- 4.8% and 104.6 +/- 2.1%, respectively. The method was linear over the concentration range from 20 to 1280 ng mL(-1) for each enantiomer, with correlation coefficients larger than 0.99 for both enantiomers. The method was applied successfully in a preliminary study of urinary excretion after administration of CAR race mate to a healthy volunteer.