USGS-NWQL: O-1402-01: Organophosphate Pesticides, Filtered Water, Gas Chromatography
|
Official Method Name
|
Organophosphate Pesticides, Filtered Water, Gas Chromatography |
|---|---|
|
Current Revision
| 2001 |
|
Media
|
WATER |
|
Instrumentation
|
Gas Chromatograph with Flame Photometric Detector |
|
Method Subcategory
|
Organic |
|
Method Source
|
|
|
Citation
|
Jha, V.K., and Wydoski, D.S., 2002, Methods of Analysis of the U.S. Geological Survey National Water Quality Laboratory - Determination of Organophosphate Pesticides in Filtered Water by Gas Chromatography with Flame Photometric Detection, U.S. Geological Survey Water-Resources Investigations Report 02-4071, 37 p. |
|
Brief Method Summary
|
Water samples (about 900 to 1,000 mL) are filtered through a 0.7-um glass-fiber filter to remove suspended particulate matter. Sample filtrate (about 1,000 mL) is pumped through disposable C-18 SPE columns. The SPE columns are dried with nitrogen to remove interstitial water. The sorbed method compounds are removed from the SPE columns by elution with 2.0 mL of ethyl acetate. The eluant is evaporated by using nitrogen to a final volume of 1 mL. Extracts are analyzed by dual capillary-column GC/FPD. |
|
Scope and Application
|
This method is suitable for the determination of 20 parent organophosphate pesticides and 5 degradation products in filtered-water samples. Seven of these compounds are reported permanently with an estimated concentration because of performance issues. The method is applicable for determining pesticides and pesticide degradates that are (1) primarily in the dissolved phase because this is a filtered-water method, (2) efficiently isolated from the sample matrix and sorbed onto a C-18 SPE column, (3) efficiently displaced from the SPE column by the ethyl acetate elution solvent, (4) chromatographically resolved and identified by using a gas chromatograph (GC) equipped with flame photometric detectors (FPD), and (5) sufficiently stable to chemical or thermal degradation to allow accurate quantification by using all sampling and analysis steps of the method. |
|
Applicable Concentration Range
|
|
|
Interferences
|
This method involves solid-phase extraction of water samples for organophosphates followed by elution with ethyl acetate. There are many organophosphate compounds in natural matrices that GC/FPD will detect. This method is designed to minimize false positives through dual GC column confirmation. Mass-spectral confirmation also should be used to confirm identification, if uncertain. Sulfur and organosulfur compounds and unknown organophosphate compounds occasionally might interfere with qualification and quantification of other individual organophosphate compounds. |
|
Quality Control Requirements
|
Minimum quality-control requirements include (1) analysis of laboratory reagent water blanks; (2) determination of surrogate standard compound recoveries in each sample blank, fortified reagent-water sample; (3) determination of compound recoveries in the fortified reagent-water sample; and (4) assessment of the GC/FPD chromatographic performance. |
|
Sample Handling
|
Samples submitted for this method must be filtered through a 0.7-um glass-fiber filter prior to isolation of method compounds by SPE. No chemical preservatives are used to preserve the compounds in the water sample, and no sample or extract holding-time studies have been performed for this method. |
|
Maximum Holding Time
|
|
|
Relative Cost
|
|
|
Sample Preparation Methods
|
USGS-WRIR 95-4105 |
