Density gradient separation of carborane-containing liposome from low density lipoprotein and detection by inductively coupled plasma spectrometry.

Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used for analyzing the new cholesterol-based compounds (BCH, BCH-Da, BCH-Db and BCH-Dc) in liposomal formulations. Not only the boron compounds but also the phospholipid compositions of the liposome formulation were quantitatively analyzed. Reasonable limit of detection for boron (0.5 µg/ml) and phosphorous (0.09 µg/ml), respectively, was observed. ICP-MS was also utilized for analyzing BCH in a brain distribution study. The detection limit of boron analysis by ICP-MS is at least three orders of magnitude lower than of that of ICP-AES (1 ng B/ml). The method was linear in the range of 500-1 ng B/ml and the linearity correlation coefficient was 1. In addition, an ultracentrifugation method was developed to separate liposomes from low-density lipoprotein (LDL). Factors such as density gradient and size of liposomes were adjusted to optimize separation and it was observed that in conjunction to time, speed and density gradient, size of the liposome also had impact on the separation using centrifugation method. These findings show the importance of ICP-AES as an analytical method for the analysis of element-based compounds encapsulated in phospholipid vesicles.