USGS-NWQL: O-2060-01:  Pesticides in Water by SPE and HPLC-MS

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Official Method Name
 Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory - Determination of Pesticides in Water by Graphitized Carbon-Based Solid-Phase Extraction and HPLC-MS
Current Revision
2001
Media
 WATER
Instrumentation
 High Performance Liquid Chromatography
Method Subcategory
 Organic
Method Source
  USGS-NWQL
Citation
 Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., Coffey, L.J., and Burkhardt, M.R., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory--Determination of pesticides in water by graphitized carbon-based solid-phase extraction and high-performance liquid chromatography/mass spectometry: U.S. Geological Survey Water-Resources Investigations Report 01-4134
Brief Method Summary
 A prefiltered water sample of 1 L is pumped through the SPE cartridge at a flow rate of 20 mL/min. After extraction, the adsorbed compounds are eluted from the SPE cartridge using two sequential elutions of 1.5 mL methanol, followed by 13 mL of an 80-percent methylene chloride and 20-percent methanol mixture that has been acidified with trifluoroacetic acid anhydride (0.2 percent). The two fractions are reduced under nitrogen to near dryness and then combined. The final volume for the extract is 1,000 uL. Analytes are chromatographically separated by HPLC using a reverse-phase octadecylsilane HPLC column, which is coupled to an electrospray ionization interface and quadrupole mass spectrometer for detection, identification, and quantitation. Each extract is analyzed twice using separate ionization modes. The first analysis is for those compounds that preferentially form positive ions under electrospray conditions, and the second is for those compounds that preferentially form negative ions. The terms "extraction" and "elution" are used to define specific actions during sample processing. Extraction is the transfer of the selected compounds from the sample onto the SPE cartridge. Elution is the removal of the selected compounds from the SPE cartridge.
Scope and Application
 The method is applicable for determining pesticides and pesticide metabolites that are efficiently isolated from the sample matrix and adsorbed onto a graphitized carbon black sorbent-filled cartridge, and chromatographically resolved and identified using an HPLC coupled by an electrospray ionization source to a quadrupole mass spectrometer. The method has been tested and validated for filtered surface water and ground water. Although not specifically tested for other aqueous matrices, it could be applied to precipitation, wastewater, tile drain discharge, and other sample types as long as the samples have been filtered using the method of Shelton (1994), and the user recognizes that performance characteristics of new matrices are not tested and any results would be provisional. Two classes of determinations are reported for samples analyzed by this method. Compounds for which the results of the determination are reported without qualification make up the first class. Compounds for which the results of the determination are reported as qualified estimates, and the concentration qualified with an "E", are in the second class.
Applicable Concentration Range
 0.025 - 1.0 (undiluted)
Interferences
 Interferences might be caused by compounds recovered from a sample matrix that contains one or more of the same ions as the selected compound and that cannot be chromatographically resolved from the selected compounds. Compared to optical detection methods typically used with HPLC, mass spectrometry is less affected by interferences, but the potential for interferences remains and requires special attention to the ratios of the characteristic ions of interest to avoid false positive detections. In addition, for the sulfonylurea and imidazolinone compound classes, sample matrix components have been shown empirically to result in an apparent increase in compound concentration (Furlong and others, 2000).
Quality Control Requirements
 Laboratory extraction samples are formed into sets, each consisting of 10 environmental samples, a set reagent spike and set reagent blank, for a total of 12 samples. Field equipment blanks and laboratory matrix spikes, whose frequency is determined by the method user, provide additional quality assurance/quality control (QA/QC). The frequency of analysis of these QA/QC samples and the aspects of the analytical process they monitor are described in the source document.
Sample Handling
 GCC - This schedule consumes the entire sample. Description: 1 L Glass bottle, amber bottle baked at 450 deg C by laboratory. Filter sample with a burned glass fiber filter. 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
 $201 to $400
Sample Preparation Methods
 USGS-WRIR 95-4105
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