Modern Water: A00224: Metribuzin in water by Immunoassay
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Official Method Name
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Metribuzin RaPID Assay Kit A00224 |
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Current Revision
| Rev. 02-04-98 |
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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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A sample and an enzyme conjugate (enzyme labeled metribuzin) are added to a sample tube, followed by addition of paramagnetic particles coated with metribuzin-specific antibodies. Both the metribuzin and enzyme conjugate compete for antibody binding sites on the particles, and bind in proportion to their concentrations. At the end of an incubation period, a magnetic field is applied to hold the paramagnetic particles. The unbound reagents are decanted and the particles are washed. The presence of metribuzin is detected by adding the enzyme substrate (hydrogen peroxide) and chromogen (3,3',5,5'-tetramethylbenzidene). The enzyme conjugate catalyzes the conversion of the substrate/chromogen mixture to a colored product. After an incubation period, the reaction is stopped and stabilized by the addition of acid. Since the enzyme conjugate was in competition with the metribuzin for the antibody sites, the color change (which is measured with a spectrophotometer) is inversely proportional to the concentration of metribuzin in the sample. The system is calibrated with metribuzin. Requirements: A clean water supply to prepare dilutions of water samples; filtration equipment to remove particulate from water samples; an SDI magnetic bead separator, required for the SDI RaPID assay kit; a spectrophotometer 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 (pre-filtration, measurement of uL volumes, rinsing, agitation), so that contact times with reagents are controlled as required; and a computerized data acquisition and processing system. |
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Scope and Application
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This method determines metribuzin in water (groundwater, surface water, well water) using immunoassay (enzyme linked immunoabsorbent assay -- ELISA). |
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Applicable Concentration Range
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0.04 - 3 ug/L |
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Interferences
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Sensitivity < metribuzin: deaminated metribuzin. Sensitivity << metribuzin: folpet, dinoseb, thiabendazole, prometon, diketometribuzin, deaminated diketometribuzin, terbutylazine. Sensitivity <<< metribuzin: carbendazim, desethylatrazine, terbutryn, butylate, pentachlorophenol, ametryn, benomyl, propazine, prometryn, cyanazine, propachlor. |
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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 immunoassay. Samples are held in a refrigerator at 4oC. Immunoassay reagents and kits are stored in the dark at 4 to 8oC 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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