How does SPE work in EPA Method 1664A specifically?
A. The SPE filter is chemically treated to make it similar in nature to the hydrophobic Oil and Grease analytes. Once the SPE filter is properly conditioned, the wastewater sample is passed through the SPE filter under vacuum. As the Oil and Grease analytes contact the SPE filter, they are stick to it and are extracted (or retained) from the wastewater sample by the SPE filter. Then the SPE filter is then air dried for a minimum of 4 minutes with vacuum at 1 CFM. This air-dry step is very important as it removes any residual water trapped in the SPE filter, which can interfere with the efficient elution of the Oil and Grease analytes with hexane. After the SPE filter is properly air dried, 3 x 10mL rinses of hexane (the final extraction solvent) are used to elute (or release) the analytes of interest from the SPE filter into the final collection container.
