Activated aluminum oxide selectively retaining long chain n-alkanes. Part I, description of the retention properties.
Aluminum oxide activated by heating to 350-400 degrees C retains n-alkanes with more than about 20 carbon atoms, whereas iso-alkanes largely pass the column non-retained. Retention of n-alkanes is strong with n-pentane or n-hexane as mobile phase, but weak or negligible with cyclohexane or iso-octane. It is strongly reduced with increasing column temperature. Even small amounts of polar components, such as modifiers or impurities in the mobile phase, cause the retention of n-alkanes to irreversibly collapse. Since n-alkanes are not more polar than iso-alkanes and long chain n-alkanes not more polar than those of shorter chains, retention by a mechanism based on steric properties is assumed. The sensitivity to deactivation by polar components indicates that polar components and n-alkanes are retained by the same sites. The capacity for retaining n-alkanes is low, with the effect that the retention of n-alkanes depends on the load with retained paraffins. These retention properties are useful for the pre-separation of hydrocarbons in the context of the analysis of mineral oil paraffins in foodstuffs and tissue, where plant n-alkanes, typically ranging from C(23) to C(33), may severely disturb the analysis (subject of Part II).
Fiselier
Katell
K
Official Food Control Authority of the Canton of Zurich, P.O. Box, CH-8032 Zurich, Switzerland.
Fiorini
Dennis
D
Grob
Koni
K
D000473:Alkanes / Q000032:analysis*; D000537:Aluminum Oxide / Q000737:chemistry*; D002853:Chromatography, Liquid / Q000379:methods*; D007536:Isomerism; D018401:Sample Size; D012997:Solvents / Q000737:chemistry; D013696:Temperature
D000473:Alkanes; D012997:Solvents; D000537:Aluminum Oxide