EPA-RCA: 8141B (by GC-NPD):  Organophosphorus Compounds in Water, Soil, and Waste Samples by GC-NPD

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Official Method Name
 Organophosphorus Compounds by Gas Chromatography: Capillary Column Technique
Current Revision
Revision 2, November 2000
Media
 VARIOUS
Instrumentation
 Gas Chromatography with Nitrogen - Phosphorus Detection
Method Subcategory
 Organic
Method Source
  EPA-RCA
Citation
  SW-846 Update IVB
Brief Method Summary
 Samples are extracted and cleaned up (according to sample matrix) and the solvent appropriately exchanged. The samples are analyzed by direct injection into a gas chromatograph with a flame photometric or nitrogen-phosphorus detector.
Scope and Application
 This method determines the concentration of organophosphorus (OP) compounds in water, soil, and waste samples by using fused-silica, open-tubular, capillary-column gas chromatography with either a flame photometric detector (FPD) or a nitrogen-phosphorus detector (NPD). Triazine herbicides can also be determined when the NPD is used.
Applicable Concentration Range
 Not Available.
Interferences
 (A) Low recoveries: Some compounds have low yield recoveries when using either the Florisil Cleanup or Gel Permeation Cleanup and, therefore, are not recommended for all compounds. However, use of alternative cleanup procedures must demonstrate that the recovery of each analyte is not below 85 percent.
(B) Flame photometric detector: Interferences from materials other than sulfur and phosphorus are minimized. If Method 3660 is used for sulfur cleanup, only the tetrabutylammonium (TBA) - sulfite option should be employed since copper and mercury may destroy OP pesticides. Recovery must not be less than 85 percent.
(C) Halogen-specific detector: May be employed for halogen-containing compounds and for the determination of Chlorpyrifos, Ronnel, Coumaphos, Tokuthion, Trichloronate, Dichlorvos, EPN, Naled, and Stirophos only. Although many OP pesticides can be detected by electron capture detection (ECD), it is not as specific as NPD or FPD. ECD should only be used when previous analyses show that interferences will not adversely affect quantitation, and that the detector sensitivity is sufficient to meet regulatory limits.
(D) Coeluting Compounds: Some compounds coelute, especially on 15-m columns. In which case, analysts should either use another column of different polarity for confirmation, use 30-m x 0.53-mm columns, or use 0.25-mm or 0.32-mm ID columns.
(E) Analytical difficulties: The method describeds numerous analyte-degradation scenarios.
(F) Method interferences: Contaminants in solvents, reagents, glassware, and other sample processing hardware may lead to elevated baselines and/or other interferences in the gas chromatograms. Routine analysis of reagent blanks should be performed as a check for method interferences.
(G) NP Detector interferences: Triazine herbicides and other nitrogen-containing compounds may interfere.
(H) Refer to Methods 3500, 3600, and 8000.
Quality Control Requirements
 Refer to Chapter One and Methods 3500, 3600, 8000, and 8270 for specific QC procedures. Procedures include: analysis of mid-level check standards, validation of extraction, cleanup, and GC operation procedures, as well as, techniques for qualitative identifications and confirmations.
Sample Handling
 See the introductory material to Chapter Four, "Organic Analytes", Section 4.0. Extracts must be refrigerated at 4oC. Organophosphorus esters will hydrolyze under acidic or basic conditions, therefore adjust samples accordingly to a pH of 5 - 8.
Maximum Holding Time
 Extract within 7 days of collection and analyze within 40 days of extraction.
Relative Cost
 $201 to $400
Sample Preparation Methods
 8140, 3510, 3520, 3540, 3541, 3620, 3660
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