Solid Phase Extraction (SPE) of PCBs & Pesticides from Water Matrix

Applicable Regulations
US-EPA SW-846 Third Edition Method 3535.

Overview of Procedure
Growing concerns for the environment, increasing costs of waste disposal, and potential exposure of employees to hazardous chemicals were among the factors that led to the development of the P2 and waste minimization initiatives in the environmental laboratory.

The extraction methods approved by EPA and other agencies prior to 1986 often involved large sample volumes requiring significant quantities of chemicals and often chlorinated solvents, which result in prohibitively expensive waste storage, segregation, and disposal costs. Reduction of chemicals and solvents at the source would reduce the costs considerably.

Keeping the above objectives in mind, the U-M Occupational Safety and Environmental Health Environmental Laboratory developed an extraction procedure to determine PCBs and pesticides in water matrix which minimized costs in labor, reagents, materials, and waste disposal. Further, the procedure described herein led to increased safety in the laboratory.

Waste Minimization Procedure
Conventional methods outlined in EPA test methods for evaluating solid waste, SW846 3510 specify that one liter of the aqueous samples should be extracted serially with a total volume of 350 mL of methylene chloride. Subsequent analysis is done by gas chromatography. The extraction is performed in a 2 L separatory funnel that is rinsed with 2 x 50 mL of the extracting solvent. Similarly, other glassware is also rinsed with small aliquots of the solvent prior to extraction. A total of 500 mL of the solvent is used per sample. In addition, the extraction and subsequent concentration of the sample extract are time consuming and labor intensive and often require two or more people and several hours to complete. In order to extract a set of 12 samples, it may take as long as six hours. Furthermore, an extensive inventory of glassware and other supporting materials are required.

For extraction of PCBs and pesticides from the water matrix, a procedure was developed based on EPA approved solid phase extraction (SPE) method, SW846 3535, which utilizes one liter of sample and less than 50 mL of solvents, methanol and methylene chloride. The SPE workstation has the capacity to process three samples simultaneously. The sample is filtered through a thin bonded polymeric disc using an aspirator vacuum, wherein the analytes of interest are trapped on the disc, and then extracted with 40 mL of methylene chloride directly into a 60 mL disposable vial. Utilization and subsequent cleaning of large 2 L separatory funnels and other glassware is completely eliminated. Three samples can be processed in 15 minutes or less saving considerable labor costs. SPE workstations with more than three positions are available for labs anticipating higher sample throughput.

Prepared samples are dried with a minimum amount of sodium sulfate, solvent exchanged for analysis by gas chromatography. The SPE procedure eliminates 90 percent solvents when compared with the conventional methods, exhibiting a significant reduction in purchase and disposal costs of chlorinated solvents such as methylene chloride. It also greatly increases safety in the laboratory by reducing potential exposure of workers to the solvents.

A standard operating procedure is available for this methodology that contains a section on P2 measures associated with this protocol.

Known Limitations
None known.

Safety & Health Precautions/Personal Protective Equipment
Follow all applicable safety and health protocols and regulations as established by your institution.

Benefits
As many as 50 to 60 samples can be processed during an eight hour shift, creating an ideal situation for a high production laboratory. Time, money, and a safer work environment than conventional methods, are all benefits of this process.

Disadvantages
None known.

Project Related Costs
Initial capital investment of $2,000 is involved as an associated cost for setting up the method. In addition, ongoing costs for disposable filter discs would be involved. The price for each disc is around $10 when bought in bulk. Conventional extraction, which requires a large area in the laboratory, personnel, glassware sets, and subsequent cleanup steps, would be eliminated. The cost savings from: labor, elimination of large sets of glassware and disposal costs must be calculated to determine the cost-effectiveness of implementing this technique.