Modern Water: 72920: 2,4-D in Water by Immunoassay
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Official Method Name
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EnviroGard 2,4-D Plate Kit 72920 (SDI 1998) http://www.sdix.com/ |
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Current Revision
| 1998 |
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Media
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WATER |
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Instrumentation
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Immunoassay |
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Method Subcategory
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Organic |
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Method Source
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Citation
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Brief Method Summary
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Inhibition immunoassay, with a colorimetric indicator for competitive binding of analyte and an enzyme-labeled conjugate to surface-immobilized antibodies. Colorimetric response is inversely related to the concentration (log) of analyte in the sample or standard. Calibrated using 2,4-D: also sensitive to 2,4-D esters. Reagents are purchased in kits with manufacturers' instructions for sample preparation and analysis. Requirements: a clean water supply to prepare dilutions of water samples; filtration equipment to remove particulates from water samples; a spectrometer which accepts sample plates (96-well) for analyses at visible wavelengths (450 nm primary; 600 or 650 nm reference); equipment to automate sample preparation for large numbers of samples (prefiltration, measurement of uL volumes, plate washing, agitation), so that contact times with reagents are controlled as required; computerized data acquisition and processing. Expendable supplies - approximately $5 per determination. |
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Scope and Application
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Ambient and compliance monitoring of 2,4-D and its esters. Can be adapted for analysis of soils by Method 4015. Screening for 2,4-dichlorophenoxyacetic acid by immunoassay (EPA 1995). |
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Applicable Concentration Range
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0.5 - 100 ug/L |
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Interferences
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Sensitivity > 2,4-D: 2,4-D esters, including 2,4-D propylene glycol ester, ethyl ester, isopropyl ester, methyl ester, butyl ester, sec-butyl ester, butoxyethyl ester, butoxy-propylene ester. Sensitivity < 2,4-D: 2,4-D isooctyl ester; 2,4,5-T; 2,4-DB; MCPA. Sensitivity << 2,4-D: MCPB; 4-chlorophenoxy-acetic acid; dichlorprop; 2,4,5-TP; dichlorphenol; triclopyr |
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Quality Control Requirements
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Recommended for a kit allowing 96 quantitative determinations: a. calibration with 3 standards and 1 blank, all analyzed in duplicate b. precision: all 44 samples analyzed in duplicate (repeats) c. accuracy: 3 matrix samples, spiked with the target analyte at different levels in the range for quantitative analysis. d. validation: analysis of 4 positive and 4 negative samples by an independent method, for confirmation |
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Sample Handling
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Samples are typically collected in glass containers with Teflon-lined caps. Drinking water samples are typically dechlorinated with 0.008% sodium thiosulfate, which does not interfere with the 2,4-D immunoassay. Samples are held in a refrigerator at 4 oC. Immunoassay reagents and kits are stored in the dark at 4 to 8 oC until use. Water samples generally need to be centrifuged or prefiltered to 0.2 um. Quantitative analysis requires dilution of highly concentrated samples, until they are bracketed by standards in the linear response range. Aliquots of samples and reagents are accurately measured (uL) and mixed for required times, following manufacturer's instructions for use of the materials purchased. |
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Maximum Holding Time
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5 days at 4oC until extraction and analysis |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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