Modern Water: A00212: Silvex (2,4,5-TP) in water by immunoassay
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Official Method Name
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Silvex RaPID Assay A00212 (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 for 2,4,5-TP. Sensitivity to 2,4,5-TP less than for 2,4,5-TP methyl and isooctyl esters, and for 2,4,5-T. 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; an SDI magnetic bead separator, required for the SDI RaPID assay kit; a spectrometer which accepts sample tubes (SDI RaPID Assay) 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, rinsing, agitation), so that contact times with reagents are controlled as required; computerized data acquisition and processing. Expendable supplies - approximately $8 per determination. |
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Scope and Application
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Ambient and compliance monitoring |
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Applicable Concentration Range
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1.4 - 250 ug/L |
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Interferences
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Sensitivity > silvex: silvex isooctyl ester; silvex methyl ester; 2,4,5-trichlorophenoxyacetic acid (2,4-5-T). Sensitivity < silvex: triclopyr; methylchlor-pyrifos; picloram; pentachlorophenol (PCP); 2,4-D methyl ester; 1,2,4-trichlorbenzene; pentachlorbenzene. Sensitivity << silvex: chlorpyrifos; 2,4-D; dichlorprop; trichloro-2-pyridinol; atrazine; MCPA; carbaryl; carbendazim; benomyl; lindane; 2,4-D isopropyl ester; 2,4-D butyl ester; 2,4-D butyric acid; 2,4-dichlorophenol; dichlorprop; lindane; toxaphene; TNT; mecoprop; 1,2-dichlorobenzene; Aroclor 1248. |
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Quality Control Requirements
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Recommended for a kit allowing 100 quantitative determinations: a. calibration with 3 standards and 1 blank, all analyzed in duplicate b. precision: all 46 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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