SOLID-PHASE EXTRACTION (SPE)

2.1 Sample preparation procedures vary by analyte group. Extraction of some groups requires that the pH of the sample be adjusted to a specified value prior to extraction (see Sec. 7.2). Other groups do not require a pH adjustment. 2.2 Following any necessary pH adjustment, a measured volume of sample is extracted by passing it through the solid-phase extraction medium (disks or cartridges), which is held in an extraction device designed for vacuum filtration of the sample. 2.3 Target analytes are eluted from the solid-phase media using an appropriate solvent (see Secs. 7.8 and 7.9) which is collected in a receiving vessel. The resulting solvent extract is dried using sodium sulfate and concentrated, as needed. 2.4 As necessary for the specific analysis, the concentrated extract may be exchanged into a solvent compatible extract with subsequent cleanup procedures (Chapter Four, Sec. 4.2) or determinative procedures (Chapter Four, Sec. 4.3) for the measurement of the target analytes.