Separation of tramadol enantiomers by capillary electrophoresis using highly sulfated cyclodextrins

In the pharmaceutical industry a continuing need for chiral resolution of drugs for various purposes and in diverse matrices exist. For these reasons, analysts may require a number of different separation systems capable of resolving a given pair of enantiomers. Highly sulfated cyclodextrins [HS-CDs] represent a relatively new class of chiral selectors in capillary electrophoresis [CE]. In this investigation the use of HS-CDs as chiral selectors in CE for enantioseparation of tramadol, a highly potent analgesic, as the model drug and the influence of the type of selector and its concentration on enantiomeric resolution were studied. All of the available HSCDs [alpha,beta and gamma] could resolve tramadol enantiomers, but HS-gamma-CD showed better resolution and a baseline resolution was achieved with this selector even at a concentration as low as 0.5% w/v. Additionally, effect of the buffer pH on the enantioresolution was studied. At low pH buffers, in which electroosmotic flow is low in CE, the negatively charged selector prevented the cationic tramadol to migrate out of the capillary even after a long analysis time of 60 minutes. However, at higher pH values [pH=7 or more], the electroosmotic flow is high enough to drag drug-selector complex toward the detector and a reasonable of the enantiomers of the drug was achieved

Effect of capillary rinsing proctol on the reproducibility of separation in capillary electrophoresis with indirect UV detection

Capillary electrophoresis [CE] with indirect UV detection is an interesting analytical method for the analysis of drugs and pharmaceuticals. Good and reproducible capillary quality is needed to develop robust methods and to facilitate method transfer in CE. It is widely accepted that preconditioning procedures are indispensable in capillary electrophoresis in order to achieve reproducibility of migration times and peak areas. In order to explore different aspects of this technique, a set of experiments were performed using vigabatrin as a model drug. The effects of capillary rinsing between each run was investigated using basic [NaOH 0.1 M] and acidic [phosphoric acid 0.1 M]-wash cycles. The results of 10 consecutive injection of the model drug after each of the two wash cycles, reveal that more reproducible results obtained when acid-wash cycle was performed as a capillary conditioning protocol. The higher pH changes during basic-wash cycle and its effects on the characteristics of the capillary inner surface were suggested as a source of greater variation between consecutive runs