On-line double focusing of atenolol and metoprolol in human urine using capillary electrophoresis with the aid of β-cyclodextrin.

A maneuverable and sensitive on-line double focusing technique combined field amplified sample stacking (FASS) with micelle to solvent stacking (MSS) with the aid of β-cyelodextrin (β-CD) is developed to detect the contents of AT and ME in human urine by capillary electrophoresis (CE) with UV detector. Small amount of β-CD not only increase the critical micelle concentration (CMC) of SDS, but also strengthen the interaction between SDS and the aimed compound by forming inclusion complexes. The result indicates that the addition of β-CD affords 5.5- and 3.5-fold improvements for atenolol (AT) and metoprolol (ME) in sensitivity than that of in the absence of β-CD in the double focusing system, respectively. Under the optimal conditions, about 200-fold improvement in sensitivity for analytes is achieved compared with conventional CE method. The limits of detection (LODs) at a signal-to-noise of 3 (S/N = 3) of the two β-blockers can be reached 3.3 and 3.7 ng mL−1 respectively, which are lower than minimum required performance levels (MRPLs) set by the World Anti Doping Agency. The relative standard deviations (RSDs) of peak areas of intra-day and inter-day are 3.51–3.38% and 2.34–4.28% (n = 6), respectively. AT and ME in urine without special pretreatment and additional instrument are analyzed. The recoveries are 82–98% with RSDs less than 2.0%.