Quantitative determination of clenbuterol, salbutamol and tulobuterol enantiomers by capillary electrophoresis

Enantiomers of clenbuterol, salbutamol and tulobuterol were directly separa ted and quantitated from a spiked sample by capillary electrophoresis (CE) using sulfated beta -cyclodextrin (SCD) as chiral selector and phosphate as running buffer. The SCD and buffer concentration, pH and field strength we re the parameters studied to optimize the separation. Optimal separation wa s obtained using 50 mM of phosphate monobasic at pH = 2.24, 0.25% (w/w) of sulfated cyclodextrin and a field strength of 10 kV, with 20 min total time analysis. Comparison between two different injection modes (hydrodynamic a nd electrokinetic) was made. In the hydrodynamic mode, repeatability (expre ssed as relative standard deviation, RSD) was less than 1.2% for migration times for all the analyte peaks and less than 2% for peak area percentages. With respect to reproducibility. RSD was less than 3.8% for migration time and less than 3% for peak area percentages. Calibration curves were set up for two different sample concentration ranges(1 to 10 mug mL(-1) and 160-8 00 ng mL(-1), of each of the racemates studied). Although the electrokineti c injection mode for an aqueous sample appeared to suffer from some enantio discrimination, calibration curves were linear in the range between 1 and 1 0 ng mL(-1) with regression coefficients ranging from 0.9996 to 0.9952. As in the case of hydrodynamic injection, the method was tested with a spiked sample.