USGS-NWQL: O-2002-01:  Pesticides and Selected Degradates in Water by C-18 Solid-Phase Extraction and GC/MS

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Official Method Name
 Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory - Determination of Pesticides and Selected Degradates in Water by C-18 Solid-Phase Extraction and GC/MS
Current Revision
2001
Media
 WATER
Instrumentation
 Gas Chromatography with Mass Spectrometry Detection
Method Subcategory
 Organic
Method Source
  USGS-NWQL
Citation
 Sandstrom, M.W., Stroppel, M.E., Foreman, W.T., and Schroeder, M.P., 2001, Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of Moderate-Use Pesticides and Selected Degradates in Water by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry: USGS Water-Resources Investigations Report 01-4098, 70 p.
Brief Method Summary
 A method for the isolation and analysis of 21 parent pesticides and 20 pesticide degradates in natural-water samples is described. Water samples are filtered to remove suspended particulate matter and then are pumped through disposable solid-phase-extraction columns that contain octadecyl-bonded porous silica to extract the analytes. The columns are dried by using nitrogen gas, and adsorbed analytes are eluted with ethyl acetate. Extracted analytes are determined by capillary-column gas chromatography/ mass spectrometry with selected-ion monitoring of three characteristic ions. The upper concentration limit is 2 micrograms per liter (ug/L) for most analytes.
Scope and Application
 The method is suitable for the determination of low-level concentrations (1 to 1,000 nanograms per liter) of pesticides and pesticide degradates in filtered natural-water samples. The methods are applicable to pesticides and degradates that are (1) efficiently partitioned from the water phase onto a C-18 organic phase that is chemically bonded to a solid porous silica matrix, and (2) sufficiently volatile and thermally stable for gas chromatography. Suspended particulate matter is removed from the samples by filtration, so this method is suitable for pesticides and degradates in the dissolved phase.
Applicable Concentration Range
 0.001-1.0 for most analytes in analysis
Interferences
 Interferences might be caused by organic compounds that have gas-chromatograph retention times and characteristic ions with a mass identical to those of the pesticides and degradates of interest. Contaminants in laboratory air, solvents, reagents (including water), glassware, sample bottles and caps, SPE columns, and sample-processing equipment can cause artifacts or false positives in the chromatograms. All of these materials must be routinely demonstrated to be free from interference [less than long-term method detection level (LT MDL), once determined] under conditions of analysis by analyzing laboratory reagent blanks. Matrix interferences might be caused by contaminants that are coextracted from the sample. The extent of matrix interferences will vary, depending on the nature of the sample matrix. Residual chlorine in treated water samples might cause degradation of some analytes, especially organophosphorus compounds (Dennis and others, 1979). Suitable reagents that might be used to dechlorinate chlorinated water samples have not been tested for their effect on all analytes. Pesticide degradates might be formed by degradation of the parent pesticide in the hot injection port of the GC. These degradates are considered artifacts of the analytical process, and are not representative of the concentration of analytes in the water samples.
Quality Control Requirements
 Method blanks, reagent spikes, surrogate spikes, certified reference material samples, continuing calibration verification standards, field blanks, field replicates, matrix spikes and matrix spike duplicates, quarterly control samples and Branch of Quality Assurance samples are analyzed. Data from these are compiled to continually monitor the QA/QC of the analysis. Each analyst must undergo technical and ethics training, perform an initial demonstration of capability, and annually demonstrate continuing capability on an analysis. Additional QA/QC practices may be added.
Sample Handling
 1L GCC - This schedule consumes the entire container. Description: 1 L Glass bottle, amber bottle baked at 450 deg C by laboratory - SOME GCCs should be filtered. CHECK METHOD REFERENCE OR EMAIL LABHELP@USGS.GOV FOR FILTERING REQUIREMENTS. Treatment and Preservation: DO NOT RINSE BOTTLE. Do not fill bottle beyond shoulder, reagents must be added to the sample at the NWQL before analyses. Chill sample and maintain at 4 deg C, ship immediately.
Maximum Holding Time
 7 days from sampling
Relative Cost
 Greater than $400
Sample Preparation Methods
 USGS-WRIR 95-4105
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