Separation and determination of pharmaceutically important polyols in dosage forms by capillary isotachophoresis

Capillary isotachophoresis (ITP) with conductometric detection has been used for separating polyols such as mannitol, sorbitol, dulcitol and xylitol. Since the polyols behave as extremely weak acids in aqueous medium, the complex-formation equilibria between boric acid and the analytes was employed to convert the neutral analytes into ionic species. The characteristic feature of this approach is the use borate, which functioned both as the complexing agent and the terminating ion. The ITP electrolyte system, optimised with respect to the sensitivity of the ITP determination and the quality of separation, consisted of 10 mM HCl+20 mM imidazole (pH 7.1) containing 0.05% poly(vinylalcohol) as the leading electrolyte and 20 mM boric acid (pH 8.1) as the terminating electrolyte. The driving and detection currents were 50 mu A (for 630 s) and 20 mu A, respectively. The effective mobilities of the borate-polyol complexes were determined; efficient separation of mannitol-sorbitol, sorbitol-xylitol and sorbitol-dulcitol mixtures was achieved. The calibration graphs were rectilinear (r=0.9995-0.9999) in the ranges 10-200 mg l(-1) of sorbitol or mannitol. The relative standard deviations were 1.4 to 1.8% (n=6) when determining 100 or 200 g l(-1) of mannitol and/or 50 to 200 g l(-1) of sorbitol in mass-produced infusion solutions. A single analysis took about 20 min. The results obtained by the ITP method were in good agreement with those of the standard pharmacopoeial iodimetric method.