One-step SFE-plus-C₁₈ selective extraction of low-polarity compounds, with lipid removal, from smoked fish and bovine milk

Abstract.

Co-extraction of lipid materials is the major source of interference in determinations of low-polarity compounds in many biological matrixes. "SFE-plus-C₁₈", a recently developed supercritical fluid extraction method employing C₁₈ adsorbent in the extraction chamber, can enable selective extraction of low-polarity compounds in lipid-rich biological matrixes without a cleanup step. This study reports the application of the SFE-plus-C₁₈ method to the quantification of: 1. polycyclic aromatic hydrocarbons (PAH) in commercially purchased smoked fish; and 2. anti-cancer agents cyclophosphamide (CP) and suberoylanilide hydroxamic acid (SAHA) spiked into homogenized whole bovine milk.

Over the course of SFE-plus-C₁₈ extraction, indigenous lipids are preferentially retained on the C₁₈ adsorbent. Compared with the conventional method, only 8–15% of the lipids in the smoked fish sample, and only 6–18% of the lipids in the milk sample, were co-extracted by SFE-plus-C₁₈. This reduction in the quantity of background lipids significantly improved chromatographic separations, retarded deterioration of the column, and dramatically improved the ability to quantify PAH present at trace levels in smoked fish by GC–MS. Using the SFE-plus-C₁₈ method, ten targeted PAH were detected in the range 9.5–13.5 ng g^–1 in the smoked fish sample. Compared with these levels, PAH extractions by use of conventional SFE gave values that were lower by 38–86%. Recoveries of CP and SAHA spiked into milk were close to 100% in both SFE-plus-C₁₈ and conventional SFE, where the lipid background during the chromatographic elution of CP and SAHA was not so severe.