USGS-NWQL: O-2437-15:  Pesticides and Pesticide Degradates in Filtered Water ...

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Official Method Name
 Determination of Pesticides and Pesticide Degradates in Filtered Water by Direct Aqueous-Injection Liquid Chromatography Tandem Mass Spectrometry
Current Revision
TM5B11
Media
 WATER
Instrumentation
 Liquid Chromatography with Tandem Mass Spectrometry
Method Subcategory
 Organic
Method Source
  USGS-NWQL
Citation
  Determination of pesticides and pesticide degradates in filtered water by direct aqueous-injection liquid chromatography-tandem mass spectrometry
Brief Method Summary
 Samples are filtered at the field site using a 0.7-micrometer (µm) nominal glass fiber filter and shipped to the laboratory. Prior to analysis at the laboratory, a 900-µL subsample is removed and placed in a 2-milliliter (mL) analytical vial. A solution of isotope-labeled (enriched) pesticides is added to the samples for use as internal standards, and 90 µL of methanol is added to modify the sample matrix for optimal chromatographic performance. Pesticides are determined in the samples in two groups, one by the MS/MS operated in positive electrospray ionization (ESI+) mode, the other in negative electrospray ionization (ESI−) mode. For each group an aliquot of the sample (100 µL) is injected onto a liquid chromatographic column (C18 phase), and the analytes are separated using binary mobile phase of formic acid/ammonium formate-methanol for ESI+ mode or acetic acid-acetonitrile for ESI− mode. A dynamic multiple reaction monitoring (MRM) method is used on the MS/MS to collect specific quantification and qualifier ions for each analyte. Analyte identification is based on agreement between known standards with respect to chromatographic retention time and the ratio of the two characteristic MRMs. The concentration of each identified component is determined using the internal standard technique.
Scope and Application
 This method was developed for determination of 229 pesticides compounds (113 pesticides and 116 pesticide degradates) in filtered water samples from stream and groundwater sites.
Applicable Concentration Range
 The range of concentrations of calibration standards is from 1 to 10,000 ng/L.
Interferences
 (A) Glassware contamination: All glassware is washed with detergent, rinsed with tap water, and finally rinsed with methanol. Nonvolumetric glassware such as sample containers, analytical vials, and micropipette bores and stainless steel spatulas must be either solvent-rinsed (with methanol) or baked in a furnace at 450 °C for 2 hours (h). Volumetric glassware must be solvent rinsed (with methanol followed by solvent used for standard). Clean glassware is covered with aluminum foil for storage. (B) Disposable item contamination: High-purity polypropylene such as transfer pipette tips, syringes, and syringe-tip filters are suitable for this tandem mass spectrometry method and must be pre-rinsed with solvent or sample prior to use. (C) Consumable contamination: Solvents, reagents, disposable transfer pipets, gloves, and other laboratory supplies should be assessed by routine laboratory reagent blanks. Identification of contaminants or interferences in MRM chromatograms will require topical blanks that examine only specific aspects of the method (solvents, vials) to identify and remove them. (D) PPE and lab contamination: Use nitrile gloves in a clean environment, and care must be taken to prevent contamination while preparing samples and standards. Material that comes in contact with samples must only be made of glass, metal, ceramics, or fluoropolymers. Replace plasticizer-containing materials such as pipette bulbs, polypropylene squeeze bottles, and Tygon tubing with plasticizer-free material such as mechanical dispensers, FEP squeeze bottles, and FEP and perfluoroalkoxy alkane (PFA) tubing. Some high-purity plastic materials can be used if shown to be contamination free using this method, for example, disposable pipette tips, filters, and syringes constructed of high-purity polypropylene.
Quality Control Requirements
 Internal standard (IS), Mixed intermediate standards (MIS), Primary dilution standards (PDS),Calibration standards (CS), Spiking solution (SS),Field matrix spikes (FMS), Field blanks (FB), Laboratory reagent blank (LRB), Laboratory reagent spike (LRS), Laboratory matrix spike (LMS, upon request), Wash blank (WBLK), Continuous calibration blank (CCB), Calibration standards (CAL), Continuing calibration verification standards (CCV), Instrument detection level standards (IDL), Instrument blank (IBLNK), Preparation spikes (PSPK), Third party check standards (TPC).
Sample Handling
 Stream and groundwater samples are filtered at the field site using small disposable 0.7-µm GF/F 25-mm-diameter syringe-tip filters or plate filters. About 10 mL of sample is pushed through the filter and collected in an amber glass 20-mL sample container that has not been rinsed with sample. A disposable 20-mL polypropylene syringe is used to push the sample through the filter. The syringe and filter are prerinsed with about 15 mL of sample to clean. Samples that might have residual chlorine should be collected in containers with dry ascorbic acid solid so that the final concentration is 0.10 g/L (1 mg for 10 mL of sample). Note that preservative studies described in this report show that ascorbic acid is not an ideal dechlorination reagent because it causes low recovery and higher variability for some of the pesticide compounds. Samples collected from autosamplers require chilling to 4 °C or preservation with methanol as a microbial inhibiter that is added to the bottles prior to sample collection at a concentration of 10 percent for optimal HPLC separation. Samples are shipped overnight to the laboratory in ice-chilled (4–6 °C) coolers. All pesticide compounds are stable for 14 days when kept chilled at 4 °C. Overnight delivery allows efficient management of samples to meet the 14-day holding time.
Maximum Holding Time
 14 days (ship overnight)
Relative Cost
 Greater than $400
Sample Preparation Methods
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