A: In this position the trapping cartridge is cleaned for trapping by washing with ethanol and then water. The sample is then applied to the trapping cartridge to perform the concentration of the materials. If necessary, the sample may require dilution or adjustment of the pH to affect the retention of the material on the trapping cartridge. The trapping cartridge is then washed with water or other solution to remove interfering materials. At the same time, the analytical system is equilibrated to minimize the analysis time. B: In this position, the trapping cartridge is moved into the flow path with the analytical column to perform the analytical analysis. C: The trapping cartridge (Valco Instruments Co. Inc, Houston, TX, Finger-tight cartridge assembly #SFECH412) can be packed by the user with any standard solid phase extraction or resin packing.