pH-Mediated field-amplified sample stacking of pharmaceutical cations in high-ionic strength samples

Capillary electrophoretic separation of samples of physiological origin typ ically have both poor resolution and efficiency due to destacking. We have previously reported a stacking method for concentration of catecholamines i n artificial dialysate, or Ringer's solution. However, pH-mediated sample s tacking of other cations has not been investigated. In this report, pH-medi ated stacking has been extended to eletripan, dofetilide, doxazosin, silden afil, UK-103,320, UK-202,581, and CP-122,288. These compounds were chosen w ithout prior structural screening except that they were cationic at the pH of our background electrolyte (BGE). Capillary electrophoretic behavior of samples in BGE is compared with those of samples in Ringer's solution with and without pl-l-mediated acid stacking. Results indicate that the peak hei ghts and efficiencies for acid-stacked samples are increased compared to th e unstacked samples in Ringer's solution or BGE. For example, the peak effi ciencies for 5 s injections of eletriptan in BGE and Ringer's solution are 138 000 and 72000 plates, respectively. In contrast, a 10 s injection of el etriptan followed by acid injection for 16 s produces a peak with 246 000 p lates. Evaluation of the stacking effect was performed by comparison of the peak height at similar peak efficiencies for samples in Ringer's solution with and without stacking. Using this method, pH-mediated acid stacking pro vides a 10- to 27-fold sensitivity enhancement for the seven cations.