Separation of PAHs in Environmental Samples by Use of Solid-Phase Extraction System for Carbon Isotope Analysis

Abstract

For precise determination of carbon isotope ratios of individual polycyclic aromatic hydrocarbons (PAHs), optimum condition to separate PAHs from unresolved complex mixture (UCM) extracted from environmental samples were examined. Two stationary phases, three eluents, and four flow rates were tested using an automatic solid-phase extraction system. PAHs standard and motorbike soot extract were used as testing sample. The results indicated (1) aminopropylsilane stationary phase (NH₂ s.p.) is superior to cyanopropylsilane stationary phase (CN s.p.), (2) n-hexane/benzene is superior to n-hexane and n-hexane/dichloromethane as the eluent, and (3) 0.03 mL min^-1 of flow rate is the most suitable. By the separation procedure with 1 g of the NH₂ s.p., approximately 75% of UCM extracted from soot sample is found to elute in fraction 1; phenanthrene, anthracene, fluoranthene, and pyrene are in fraction 2; and the PAHs heavier than chrysene are obtained as fraction 3. In the case of environmental samples such as a lake sediment and an aerosol sample, UCM interfering isotope measurement of co-eluted PAHs was not observed in fractions 2 and 3. Thus, this procedure can be applied to δ¹³C measurement of PAHs over “3-ring” in environmental samples containing UCM with a precision of 1.2‰. Reproducible elution condition is obtained by using a computerized separation system. No significant carbon isotopic fractionation of PAHs was observed during this separation procedure.