Ultra-Low Analysis of Pesticides and PCB Aroclors in Ground Water
The toxicity and environmental impact of organochlorine pesticides and polychlorinated biphenyls (PCBs) is well documented. Routine environmental analysis of these compounds has remained largely unchanged since the advent of EPA method 8081 and EPA method 8082. However, recent instrumental advances and implementation of ultra-trace extraction techniques have allowed for significant improvements in detection limits.
The CAS Kelso laboratory has developed procedures that produce detection limits low enough to meet the requirements of the majority of studies. The extraction and analysis procedures include modifications to increase sensitivity, but still meet the requirements of the traditional EPA SW846 methods. Samples are prepared according to EPA Method 3520C with modifications, including a 2L continuous liquid-liquid extractor. Special glassware handling techniques are incorporated to minimize potential background contamination.
Development work is in progress to migrate the procedure to solid phase extraction (SPE) resulting in enhanced method performance. The instrumental portion of the analysis meets EPA Method 8081/8082 requirements. Combining Agilent Gas Chromatograph (GC) equipped with a micro-electron capture detector (micro-ECD) and a programmable temperature vaporizing (PTV) inlet with increased sample volume, ground water detection limits can be reduced ten to forty-fold over the limits listed in the methods.
Table 1 shows the current Method Detection Limits (MDL), Method Reporting Limits (MRL), and the mean recoveries. A relatively high level of accuracy can be achieved at or near the lowest point in the calibration curve (i.e., considering the levels spiked, the recoveries are excellent).
Unlike conventional split/splitless inlets, several hundred microliters can be injected into a PTV inlet. The PTV injector is cryogenically cooled and the excess solvent is vented. When most of the solvent is eliminated, the vent is closed and the target analytes are swept onto the column. Programming the PTV inlet properly is critical. Optimization of vent time and temperature are important in eliminating enough solvent while retaining the analytes of interest. Liner selection is also critical in retaining target compounds while the solvent is swept away. A Gerstel multi-baffled liner coated with 2μm of VB5 (5% diphenyl/95% dimethyl polysiloxane), supplied by Valco Instruments Company, Inc. (VICI), retained the lower molecular weight pesticides and Aroclors and consistently met the EPA criteria for 4,4’-DDT and Endrin analyte degradation.
As mentioned, sample preparation is critical to being able to utilize the potential of the instrumentation. Emphasis must be placed on careful handling of samples and extracts to avoid background contamination and/or loss of analyte during the procedure. If the proper techniques are employed, excellent sensitivity can be achieved.