Chromatographic Separation
Modified chromatographic adsorbents consisting of silica gel impregnated with metal salts facilitate the separation of complex hydrocarbon mixtures. During the analysis of mineral oils in paper and board, silver nitrate silica acts as the stationary phase in cleanup columns to separate saturated hydrocarbons from aromatic hydrocarbons. This cleanup is essential for preventing overlapping chromatographic signals.
Coordination Chemistry
Electron interactions govern the separation process in silver-impregnated media. The silver ions bonded to the surface of the silver nitrate silica form weak reversible pi-complexes with the double bonds of aromatic hydrocarbons and olefins. Saturated hydrocarbons do not possess double bonds and therefore pass through the column without being retained, eluting in the first fraction.
This chemical selectivity allows analysts to isolate the aromatic hydrocarbon fraction by subsequently flushing the column with a more polar solvent, ensuring that both chemical groups are measured independently without cross-contamination.
Fractionation Quality
Protecting the column from light and moisture is necessary to prevent the degradation of silver ions. When silver nitrate silica is exposed to ambient light, the silver reduces to metallic silver, which diminishes the column’s separation efficiency. Adhering to strict storage and handling conditions ensures reliable fractionation of saturated and aromatic mineral oils.
