USGS-NWQL: O-5404-02: Organophosphate pesticides, bottom sediment, high-performance gel-permeation chromatography, gas chromatography
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Official Method Name
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Organophosphate pesticides, bottom sediment, high-performance gel-permeation chromatography, gas chromatography |
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Current Revision
| 2002 |
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Media
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SOILS/SEDIMENT |
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Instrumentation
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Gas Chromatograph with Flame Photometric Detector |
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Method Subcategory
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Organic |
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Method Source
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Citation
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Jha, V.K., and Wydoski, D.S., 2003, Methods of Analysis of the U.S. Geological Survey National Water Quality Laboratory ? Determination of Organophosphate Pesticides in Bottom Sediment by Gas Chromatography with Flame Photometric Detection, U.S. Geological Survey Water-Resources Investigations Report 02-4222, 38 p. |
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Brief Method Summary
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Minimum sample size of about 25-g equivalent dry-weight sample, accurately weighed, is extracted with Soxhlet apparatus using 350 mL dichloromethane and 25 mL methanol (93:7 ratio). The extract is concentrated and then filtered through a syringe filter containing a 0.2-um polytetrafluoroethylene membrane. 1,400-uL aliquot of the sample extract is injected quantitatively onto two linked styrenedivinylbenzene gel-permeation chromatographic columns and eluted with dichloromethane. The aliquot is concentrated and solvent exchanged to ethyl acetate. The extract is evaporated by using nitrogen to a final volume of 0.5 mL. Extracts are determined by dual capillary-column GC/FPD with external standard quantitation method. |
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Scope and Application
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This method is suitable for the determination of 20 parent organophosphate pesticides (OPs) and 5 related OP degradation products in bed-sediment (lake and stream), aqueous suspended-sediment, and soil samples. One of the compounds, O-ethyl-O-methioate, is permanently reported with an estimated concentration because of variable instrumental and extraction stability problems. This method is applicable to the determination of pesticides and pesticide degradates that are (1) efficiently extracted from the solid matrix by methanol and dichloromethane, (2) adequately separated from natural coextracted compounds by gel permeation chromatography, (3) chromatographically resolved and identified by using a gas chromatograph (GC) equipped with flame photometric detectors (FPD), and (4) sufficiently stable to chemical and thermal degradation to allow accurate quantification by using all sampling and analysis steps of the method. |
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Applicable Concentration Range
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Interferences
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Sulfur and organosulfur compounds and unknown organophosphorus compounds occasionally might interfere with identification and quantification of many organophosphate compounds. There are many organophosphate compounds in natural matrices that GC/FPD will detect, because this procedure involves methylene chloride extraction of sediment samples. This method is designed to minimize false positives through dual GC column confirmation. Mass spectral confirmation may be used to confirm identification if there is uncertainty caused by complex matrix samples. |
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Quality Control Requirements
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Minimum quality-control requirements include the following: (1) analysis of laboratory reagent sodium sulfate blank; (2) determination of surrogate standard compound recoveries in each sample, blank, and fortified reagent sodium sulfate sample; (3) determination of compound recoveries in the fortified reagent sodium sulfate spike sample; and (4) assessment of the GC/FPD chromatographic performance. |
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Sample Handling
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Ship samples, contained in 1,000-mL wide-mouthed glass jars with lids lined with polytetrafluoroethylene (PTFE) on ice via overnight carrier to the laboratory as soon as possible following collection. Allow sufficient space for expansion of the sample if frozen. Following login at the laboratory, samples are stored at -15oC in freezers until time of analysis. Sample holding times for this method have not been established. |
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Maximum Holding Time
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Relative Cost
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Sample Preparation Methods
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