Abstract
We established a separation procedure of sedimentary straight-chain and cyclic fatty acids by urea adduction to facilitate GC/C/IRMS analysis. The procedure involves a mixing of the monocarboxylic methyl ester fraction with 15% (w/v) urea in MeOH (200μl), ethyl acetate (300μl) and n-pentane (500μl) at room temperature. After drying the solvents under N2 flow, the non-adduct fraction (cyclic compounds) is washed with n-hexane (3×1.5ml) (mean recovery: 91%). The residue is dissolved in water (4ml) and the adduct fraction (straight-chain compounds) is subsequently extracted with n-hexane/ether (9:1v/v; 3×1.5ml) (mean recovery: 87%). The separation we apply here was confirmed not to affect the isotopic composition of the straight-chain and the cyclic fatty acids.
