Multidimensional on-line solid-phase extraction (SPE) using restricted access materials (RAM) in combination with molecular imprinted polymers (MIP)

A novel, multidimensional SPE sample-processing platform for complex fluids , which relies on the combination of small LC columns packed with restricte d access materials (RAM) and molecular imprinted polymers (MIP) is describe d. It is called the Six-S ProcEdure (Six-SPE). Six-SPE involves a size-sele ctive sample-separation step followed by a solvent-switch. Six-SPE efficien tly removes interfering matrix components of complex aqueous samples and cr eates optimal conditions for selective recognition, i.e. binding of the imp rinted target analyte(s). A SixSPE analysis cycle consists of four distinct steps: 1. separation of a given sample (e.g. plasma, urine, saliva, milk, etc.) by adsorptive extraction (e.g. reversed-phase partitioning) of low molecular weight components on to the stationary phase of a RAM column and simultaneo us size-exclusion, i.e. quantitative disposal of macromolecular matrix cons tituents to waste; 2. desorption and transfer of the extract from the RAM column on to a serie s-connected MIP column using a pure organic mobile phase (e.g. acetonitrile ) [solvent switch]; 3. molecular recognition, i.e. selective binding of the target analyte(s) b y a tailor-made MIP column; and 4. desorption and transfer of the analyte fraction on to a series-connected separation (e.g. HPLC) and/or detection system (e.g. UV, FD, MS). As a first application we coupled the Six-SPE platform to a conventional HP LC system for on-line analysis of the analgesic drug Tramadol in human plas ma using LiChrospher ADS RP-18 as a RAM precolumn for the fractionation ste p in the first and second chromatographic dimension and a Tramadol imprinte d polymer for the molecular recognition step, i.e. third chromatographic di mension.