Method Modifications for EPA Method 1664A Using Automated SPE

Historically, methanol was used to activate and dry solid phase extraction (SPE) disks but, in January of 2009, the Environmental Protection Agency (EPA) released a modification to their 1664A method disallowing its use as a co-solvent in the determination of n-Hexane extractable materials (HEM). This decision caused a great deal of turmoil within the SPE world.A series of tests were run on influent samples from a wastewater treatment plant using liquidliquid extraction (LLE) and SPE with and without methanol as a drying agent. These test proved that, for spikes with no matrix interference, the results for LLE and SPE with methanol were comparable to those of SPE without methanol. However, when using a raw wastewater influent sample, results of SPE without methanol had over a 42 percent reduction in HEM recovery compared to samples run using LLE and SPE with methanol. Without a drying agent such as methanol, an influent sample can encapsulate the HEM within its matrix giving significantly lower recoveries during the SPE process.Upon further communication with the EPA, methanol was allowed in a restricted sense. It could be used to activate the disk and then later to break the matrix encapsulation provided that it all be sent to waste and not eluted. With the methanol back in place, both the disk activation and the matrix encapsulation problems have been solved and HEM recoveries for automated SPE are now averaging 98 percent in laboratory tests.