Sub-critical fluid extraction of morphinic alkaloids in urine and other liquid matrices after adsorption on solid supports

Supercritical fluid extraction (SFE) of liquid matrices is difficult and requires special instrumentation. An alternative is to load the liquid on a solid support prior to extraction. This procedure yields higher selectivity and can be used as a clean-up step when very complex liquid matrices, such as urine, are to be analyzed. This paper demonstrates the use of various solid supports in order to extract morphinic alkaloids with subcritical fluids (CO2 + polar modifier). Optimization of the procedure with regard to loading conditions, SFE parameters such as pressure, extraction time, flow rate and eluent composition, was carried out with morphinic alkaloids in aqueous solution. As a real-life application, SFE of opiates in urine were tested with two silica bonded phase supports (C18 (polygosil 60-4063, from Macherey-Nagel) and Bond Elut Certify from Analytichem International). Recovery, variation coefficients and linearity are described for each procedure. Bond Elut Certify silica was chosen as the best solid support and SFE is compared with conventional solid phase extraction