Liquid Chromatography - Liquid Chromatography Applications 5
In order to identify the impurities, the column had to be significantly overloaded. Despite this, the impurities were well separated from the main component and a substance was shown to be present in the generic formulation that was not in the Darvocet®. The mobile phase was 98.5% dichloromethane with 1.5% v/v of methanol containing 3.3% ammonium hydroxide. The ammoniacal methanol deactivated the silica gel but the interaction of the solutes with the stationary phase would still be polar in nature. In contrast solute interactions with the methylene dichloride would be exclusively dispersive.
Courtesy of Supelco Inc.
Figure 59. The Analysis of Acetaminophen Formulations
Ion chromatography can be used in a number of novel ways and employing the appropriate conditions can even be used to separate mixtures where the components are not ionic or do not normally produce interactive ions in aqueous solution. An example of this type of separation is the analysis of saccharide mixtures using ion exchange interactions. An illustration of such a separation is given in figure 60. The saccharides are reacted with a borate with which saccharides readily forms complex anions. The procedure for making the complex is simply and is achieve by merely including a borate buffer in the mobile phase. The process is, in fact, a form of 'in-line' derivatization.