Final Evaluation of US EPA Method 3546: Microwave Extraction, a Microwave-Assisted Process (MAPTM)* Method for the Extraction of Contaminants Under Closed-Vessel Conditions

Abstract

Microwave-assisted extraction, a MAPTM technology, has been the subject of enhanced interest from the environmental sector in the last few years as a result of the need for methodologies that improve sample preparation without compromising the quality of the data while being environmentally sustainable. Liquid-phase microwave-assisted extraction offers such advantages: it is a very fast extraction technique, it consumes less solvent and energy, and it is cost effective. A preliminary validation study involving closed-vessel apparatus and contaminants such as PAHs, PCDDs/PCDFs, chlorinated pesticides, and PCBs was performed (Li et al., 1996). Excellent performance and precision were achieved for these analytes (Li et al., 1996). In order to fully evaluate the method for a wider range of analytes an interlaboratory study was performed. A round-robin study was performed with five laboratories carrying out the extraction portion. This study also involved thermally labile and potentially reactive RCRA target analytes such as phenols, phenoxyacid herbicides, and organophospho-rus pesticides. Three split samples were used by each laboratory using methodologies stipulated in a single standard operational procedure (SOP). The extractions from the five laboratories were sent to a single laboratory who performed all the analyses in order to minimize the variability of the results due to the determinative procedure. Clean up was performed using standard procedures and analyses were done according to the appropriate US EPA SW-846 methods. The broad range of applicability, the reduced sample preparation time, and the reduced amount of solvent used all contribute to achieving sustainable environmental protection goals. Furthermore, the reduced operational costs associated with the protocol — compared to conventional Soxhlet, for example — are significant and prove valuable in these times where the “greening” of the laboratory usually gives rise to higher operating costs. Further work involving open-vessel apparatus is under way.