Determining trace amounts of contaminants in water

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Courtesy of Horizon Technology, Inc.

Introduction
Pesticides, polychlorinated biphenyls (PCBs), and pharmaceuticals are a worldwide contamination problem. Several major US water bodies, such as the Hudson River, St. Lawrence River, Fox River and the Great Lakes have been contaminated with PCBs from industries discharging into these water bodies for decades. For example, from approximately 1947 to 1977, the General Electric Company (GE) discharged as much as 1.3 million pounds of PCBs from its capacitor manufacturing plants at the Hudson Falls and Fort Edward facilities into the Hudson River. GE is now paying for clean-up and monitoring efforts.

Studies have confirmed that many of the contaminants that were previously discharged into the environment have undergone degradation, weathering, vaporization and sedimentation. The contaminants may no longer resemble the original mixture and pattern. In particular, PCB contaminants may still be present, but in different amounts and altered patterns, called congeners. With the improvement of analytical techniques over the past 25 years, investigators are now looking closer at individual congeners. With these investigations, a shift in analysis has occurred from total contaminants analysis to congener specific analysis. This development has led to a greater need for versatility in PCB analysis.

Because many of these contaminants are long lived in the environment and bio-accumulate throughout the food chain, numerous regulations have been developed and implemented. Demands have been placed upon environmental testing laboratories to increase sample throughput, shorten sample turnaround times, achieve reproducible results, and provide lower detection limits. The analysis of water for a full spectrum of contaminants has proved to be very challenging. With tighter regulation and lower-level detection limits being required by regulating authorities, analytical laboratories have to find improved methods of extraction.

Traditional methodologies typically involve a manual separation funnel in a method called Liquid-Liquid Extraction (LLE) or a more exhaustive extraction technique called Continuous Liquid-Liquid Extraction (CLLE). These methods require a large volume of solvent, such as dichloromethane, in a process that causes contaminants to transfer from the water sample to the solvent. The extract is then concentrated through an evaporation step; solvent is exchanged with hexane, with the final extract now ready for analysis. These methods were originally developed for analysis of all types of water samples and worked very well for samples with high concentrations of contaminants. However, with the necessity of trace analysis for PCBs and other contaminants present in water, these methods are proving to be outdated and inadequate. They are labor intensive, use large amounts of solvent and require contaminant-free glassware. This limits the number of samples a laboratory can process in a day, makes reproducible results difficult and does not allow for lower detection limits.

The implementation of an optimized and automated Solid Phase Extraction (SPE) method overcomes all these issues. The development of automated extraction and cleanup processes has resulted in less solvent use, glassware and extraction time, while producing trace detection at a much lower-method detection limit (MDL.) This last issue has become the most important.

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