AN 18 - Automated Measurement of δ13C for Identifying Edible Oils

Edibles oils are derived from a wide variety of plant species including several types of nuts, seeds, and corn (maize). These vary significantly in cost and perceived value because of their taste and other quality parameters. Consequently, there is an economical incentive for unscrupulous adulteration of higher value and gourmet oils by dilution with lower cost (e.g. corn) alternatives, at several points along the supply chain. In addition to the fraud aspects, such un- recorded adulteration can have potentially negative consequences to consumers with strong allergic reactions to specific product types.

Stable isotope ratios have long been known to have enormous potential for food source screening, including the specific case of edible oils¹. Although the stable carbon isotope value, δ¹³C, is very sensitive to plant type, this potential has remained largely unexploited because of the considerable difficulty, time and cost of obtaining this type of data with traditional IRMS instrumentation. In this application note we present isotopic carbon analysis data of samples from three different edible oils – sesame, soybean and corn. The data were obtained in minutes, using a totally new type of turnkey isotope analyzer, the i-TOC-CRDS, jointly developed by Picarro and OI Analytical. This device integrates a combustion chamber front-end from OI which converts solids, semi-solids and liquids into CO₂. This gas is then automatically injected into Picarro’s wavelength scanned cavity ring down spectroscopy (WS-CRDS) detector for a high precision isotopic carbon measurement.