Fluorescence determination of sulphobutylether-β-cyclodextrin sodium in human plasma and urine by size-exclusion chromatography with inclusion complex formation

HPLC methods with fluorescence detection have been developed for the determination of sulphobutylether-β-cyclodextrin sodium (SBECD), a novel excipient for use with drugs of limited aqueous solubility, in human plasma and urine. SBECD contains no chromophore or fluorophore but can be detected by size-exclusion HPLC using excitation and emission wavelengths of 290 and 360 nm when 1-naphthol is included in the mobile phase. The guest-host inclusion complex SBECD forms with the 1-naphthol restores the quenched fluorescence in the mainly aqueous environment of the mobile phase. Using simple solid phase extraction, recoveries of 41% were obtained using aminopropyl cartridges for urine and of 69% using end-capped cyclohexyl cartridges for plasma. These extracts were analysed using size exclusion HPLC. Both methods were precise, accurate and simple to perform. The working ranges were 4 to 200 μg mL⁻¹ and 50 to 1500 μg mL⁻¹ for plasma and urine respectively. The lower limits of quantification were 4 μg mL⁻¹ for plasma and 50 μg mL⁻¹ for urine. The methods were also selective; no significant interferences were observed in six different sources of plasma or urine, or from a range of likely co-medicants.