Application of Column Chromatography for Accurate Determination of the Carbon Isotopic Compositions of n-alkanes in Diverse Environmental Samples

Abstract

The carbon isotopic compositions (delta C-13) of n-alkanes in various environmental samples have been previously proposed as suitable fingerprints for assessing the origin of organic matter (OM) in diverse environmental systems. However, with respect to using gas chromatography-combustion-isotope ratio mass spectrometry for the carbon isotopic analysis of n-alkanes, analytical uncertainty may often be caused by the co-elution of interfering unsaturated compounds (e.g., aromatic and branched compounds). Hence, we propose a simple but reliable method for purification that uses column chromatography. The performance of two different solid stationary phases (i.e., aluminum oxide and Ag+-impregnated silica) was compared in terms of their capacity to eliminate unsaturated compounds from total hydrocarbons and thus increase the precision of delta C-13 measurements. Compared to the use of an activated aluminum oxide column, elution from an Ag+-impregnated silica column allows more effective isolation of individual n-alkanes, which results in more precise delta C-13 measurements for diverse environmental samples. Thus, Ag+-impregnated silica column separation can be effective as a routine experimental technique for increasing the accuracy of the delta C-13 values for n-alkanes in OM, which includes a large proportion of unsaturated compounds.