Direct and simultaneous determination of intra-liposomal and external sulfate in liposomal doxorubicin formulations by capillary electrophoresis/inductively coupled plasma-tandem mass spectrometry (CE/ICP-MS/MS).

A capillary electrophoresis coupled to an inductively coupled plasma-tandem mass spectrometry (CE/ICP-MS/MS) method was developed and validated for the determination of external and intra-liposomal sulfate in doxorubicin liposomal formulations. Ammonium sulfate is a critical component of liposomes, in the loading and maintenance of drug in the intra-liposomal space. Complete separation of external and intra-liposomal sulfate was achieved using CE with minimal liposome disruption. The current filtration technique induces intra-liposomal sulfate leakage during the separation as a result of rupture of liposomes. CE was coupled to a triple quadrupole ICP-MS detection method that allows direct quantification of intra-liposomal sulfate without the need of disintegration of liposomes. Three FDA-approved brand name and generic doxorubicin liposomal formulations were compared for total sulfate and external sulfate. In addition, batch-to-batch product quality consistency was analyzed by comparing the total sulfate and external sulfate for the brand name formulation. Slight variations were observed in total sulfate among the different formulations, and the total sulfate was consistent between different batches of brand name formulation. However, the external sulfate concentration was significantly different among all the tested doxorubicin liposomal formulations. Nevertheless, the interior sulfate is higher than the exterior sulfate concentration to keep the doxorubicin encapsulated by maintaining the ion gradient. This fast and direct sulfur analysis method could be potentially used to quantitative analyze liposomal formulation for quality control.