Optimization and validation of a capillary zone electrophoresis (CZE) method for the determination of inner and external inorganic sulfate from doxorubicin-loaded liposomes as a measurement of encapsulation efficiency are presented. Sulfate was determined using a fused silica capillary (50 cm x 75 μm ID) and background electrolyte (BGE) composed of 5 mM chromate with 1 mM of TTAB at pH 10.5 with indirect UV detection at 254 nm. The separations were achieved at temperature of 25 ºC, 5 kV of reverse applied voltage using a pressure of 0.5 psi for 5s of sample introduction. Sulfate quantitation from the outside of liposomes was obtained by simple dilution of the liposome sample but an extraction with a non-ionic surfactant and a mixture of methanol-chloroform-water were necessary to breakdown the liposomes for the quantitation of the total sulfate (inside and outside) with acceptable recovery percentages (96.3% to 102.6%). Parameters of validation were evaluated according to ICH guidelines such as specificity, linearity, LOD, LOQ, accuracy, precision and robustness. The proposed CE method resulted to be suitable for the inner and external sulfate analysis of doxorubicin-loaded liposomes for routine quality and stability control studies.
Keywords: Doxorubicin encapsulation, liposomes, sulfate, capillary zone electrophoresis.